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Making a Perfect Cuppa
| | Use a good quality loose leaf or bagged tea This must be stored in an air-tight container at room temperature Always use freshly drawn boiling water In order to draw the best flavour out of the tea the water must contain oxygen, this is reduced if the water is boiled more than once. Measure the tea carefully Use 1 tea bag or 1 rounded teaspoon of loose tea for each cup to be served Allow the tea to brew for the recommended time before pouring Brewing tea from a bag in a mug? milk in last is best |
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Recommended Brewing Times
| Name of tea | Country | Type | Brewing Time | With or without Milk | | Gunpowder | China | Green | 3-4 minutes | without | | Jasmine | China | Green flavoured with jasmine flowers | 2-3 minutes | without | | Oolong | China or Taiwan | Oolong | 5-7 minutes | without | | Lapsang Souchong | China or Taiwan | Black | 4-5 minutes | without | | Sencha | Japan | Green | 2-2 1/2 minutes | without | | Genmaicha | Japan | Green flavoured with popped rice and corn | 3-4 minutes | without | | Darjeeling | India | Black | 2-3 minutes | without | | Assam | India | Black | 3-4 minutes | with or without Milk | | Ceylon Uva | Sri Lanka | Black | 3 minutes | with or without | | Ceylon Dimbula | Sri Lanka | Black | 3-4 minutes | with or without | | Kenya | Kenya | Black | 2-3 minutes | with |
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Buying and Storing Tea
Use a good quality Tea Supplier
Store tea in a cool, dry place, avoid placing it next to strongly flavoured or perfumed foods etc
Do not over buy tea
In some parts of the country the tap water is chlorinated strongly and this can affect the taste of the tea, if you are based in such an area consider using a water filter.
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Tea & Health
Health Benefits of Tea
Tea has many important vitamins, minerals and antioxidants needed by the human body. This is why tea has been used as a medicine for many years and is, with the backing of modern research, still touted for its health benefits. Drinking tea has been associated with good oral health and prevention of certain cancers and heart diseases.
VITAMINS
Black tea contains small amounts of certain essential vitamins listed below. Each has an important and unique function necessary for maintaining health.
Carotene - a precursor to Vitamin A (Retinol) serves as an antioxidant.
Thiamine (B1) and Riboflavin (B2) - both play an integral part in releasing energy from food.
Vitamin C - is important in maintaining a healthy immune system. It functions as an antioxidant, aids detoxification and acts as a structural component in the collagen fibers of gums.
Folic Acid - plays a role in cell division and amino acid synthesis.
Nicotinic Acid and Panthothenic Acid - are important for the release of energy from carbohydrates and fats.
MINERALS
Tea is also a rich source of three very important minerals:
Manganese - this is a co-factor for an enzyme known to prevent oxidative damage. Drinking several cups of tea a day can provide you with almost half your daily manganese requirement.
Potassium - is one of the body's main electrolytes and thus plays a critical role in water balance as well as the body's acid-base balance. Potassium is also necessary for the transmission of nerve impulses. A deficiency results in aberrant heartbeats, fatigue and localised cramping.
Fluoride - this is another mineral found in great abundance in tea. In fact, tea is one of the very few natural sources of fluoride. Fluoride has made its mark as the most successful agent against tooth decay. Scientists encourage drinking tea to improve oral health and to prevent tooth decay and gum disease.
ANTIOXIDANTS
Oxidation of our body elements results in the formation of very reactive substances known as free radicals. Free radicals cause damage to our cells, which can eventually lead to heart disease and cancer. Antioxidants found in our diet help prevent free radical formation and repair damage caused by free radical attack. Vitamins A, C and E are popular antioxidants. Both green and black teas also contain antioxidants known as flavenoids. Flavenoids play a critical role in protecting us from heart disease and cancer.
Now that you know the health benefits of drinking tea. go ahead and drink up, your body needs it!
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Tea and Antioxidant properties
Introduction
Increasing evidence is highlighting the role antioxidants may have in protecting against certain conditions such as heart disease, stroke and cancers. It has been proposed that the mechanisms leading to these diseases may be promoted by free radicals and that antioxidants may oppose the action of these molecules. In addition to the well known antioxidants such as Vitamins C and E, there is growing research demonstrating the potentially beneficial effects of plant-derived antioxidants, polyphenols, found in fruits, vegetables, nuts, cereals and drinks such as tea and red wine.
Free radicals explained
Free radicals are unstable molecules that include the hydrogen atom, nitric oxide (NO) and molecular oxygen (O2). These naturally occur in the body as a result of chemical reactions during normal cellular processes. They can also be formed in response to excess pollution, too much UV sunlight and exposure to cigarette smoke. In an attempt to stabilise, they attack other molecules in the body potentially leading to cell damage and triggering the formation of another free radical resulting in a chain reaction. Some scientists believe that this type of free radical action has been implicated in certain chronic and ageing diseases such as cancer, heart disease, stroke, rheumatoid arthritis, cataracts and Alzheimer's disease.
Protective mechanisms of antioxidants
Antioxidants are compounds that help to inhibit the many oxidation reactions caused by free radicals thereby preventing or delaying damage to the cells and tissues. Their mechanisms of action include:-
Scavenging reactive oxygen and nitrogen free radical species
Decreasing the localised oxygen concentration thereby reducing molecular oxygen's oxidation potential
Metabolising lipid peroxides to non-radical products
Chelating metal ions to prevent the generation of free radicals
In this way antioxidants limit the free radical damage from:-
Oxidising Low Density Lipoprotein (LDL) cholesterol, which may increase the risk of athersclerosis
Promoting platelet adhesion, which can lead to thrombosis thereby increasing the risk of heart disease or stroke
Damaging the cell's DNA, which may lead to cancer
Blocking the normal endothelial cell function and vasodilatation in response to nitric oxide, a potential mechanism for heart disease and cancer
Triggering inflammation
Impairing immune function
Some antioxidants are synthesised within the cells themselves (endogenous) and others need to be provided in the diet. Table 1 gives examples of antioxidants with established or proposed activity in the body.
Table 1
Endogenous Antioxidants Antioxidants provided in the diet
Polyamines
Melatonin
Oestrogen
Superoxide dismutase
Glutathione peroxidase
Catalase
Lipoic Acid
Caeruloplasmin
Albumin
Lactoferrin
Transferrin Vitamin E
Vitamin C
Carotenoids
Polyphenols
Copper
Sources of dietary antioxidants
Traditionally dietary antioxidants were thought of as Vitamin E and C and the carotenoid - carotene. In recent years there has been particular interest in the antioxidant activity and health benefits of other phytochemicals. Table 2 lists two examples of phytochemicals and their food sources.
Table 2
Phytochemical Categories Sub-category Food Sources
Carotenoids Carotene -carotene Carrots, pumpkins, avocados
b- carotene Carrots, red peppers, apricots, spinach
Lycopene Tomatoes, pink grapefruit, watermelons
Lutein Spinach, kale, brussel sprouts
Polyphenols Flavonoids Anthocyanins Berries, red wine, black grapes
Flavones Celery, parsley, olives
Flavonols; Quercetin, Rutin Tea, apples, onions, wine, garlic
Flavonols; Catechins Tea, wine, pears, apples, chocolate
Flavanones Citrus fruit
Isoflavones Legumes
Phenolic Acids Hydroxybenzoic Acid; Gallic Acid, Ellagic Acid, Salicylic Acid Berries, Tea, Grapes, Walnuts
Other Phenolic compounds Capsaicin Chillies, Peppers
Tannins Tea, red wine, grapes
Tea has one of the highest total flavonoid contents of all plants at 15% of the leaf by dry weight1 and is also the major source of flavonoids in the UK diet, providing approximately 80% of dietary flavonoids for the population as a whole.
Tea Flavonoids
The types and amounts of flavonoids present in tea will differ dependent on the variety of leaf, growing environment, processing, manufacturing, particle size of ground tea leaves and infusion preparation. 2-4 Typically 93% of total tea phenolic compounds are flavonoids 1. Green teas contain more of the simple flavonoids called catechins, while the oxidisation that the leaves undergo to make black tea converts these simple flavonoids to the more complex varieties called theaflavins and thearubigins. For more information about green and black teas please refer to the fact sheet 'Black and Green Tea: How do they differ?'
Tea flavonoids are water-soluble and one study1 has shown that a cup of UK tea that has been allowed to brew for 40-60 seconds will typically deliver approximately 140mg of flavonoids whilst a second carried out by the UK Tea Trade Technical Committee2 using typical UK consumer brewing conditions and encompassing the range of blends and bag weights commonly on sale in the UK gives a figure of 125mg/235ml serving. The longer the tea is left to brew, the higher the concentration of flavonoids.
Tea flavonoids demonstrate antioxidant activity 5-8 and while not a replacement for fruit and vegetables, the antioxidant activity of tea has been compared to that of fruit and vegetables in a number of studies. One study concluded that at the typical UK daily consumption of 3 cups a day,9 tea has approximately the same antioxidant power as eating six apples.10 Another study found that one or two cups of tea has the same 'radical scavenging capacity' as five portions of fruit and vegetables or 400mg vitamin C equivalents.
Health benefits of tea flavonoids
For many years it has been known that the plant polyphenols are antioxidant in vitro, in fact many common flavonoids are several times more potent than Vitamin C or E12,13. This growing interest in the antioxidant activity of phenolic compounds has led to increased research into their potential health benefits e.g.
Heart Disease and Stroke
Several reports indicate that tea flavonoids inhibit the oxidation of LDL cholesterol in vitro
A reduction in blood lipids has been demonstrated in animal studies
Certain tea flavonoids exhibit anti-inflammatory actions in animals. Athersclerosis is a disease with a strong inflammatory component
Improvements in blood vessel function, specifically the vascular endothelium, has been seen in patients with established CHD23
Several in vitro studies and one human trial have found that platelet aggregation can be inhibited by various flavonoids
The antioxidant activity of tea flavonoids may account for the results of a number of epidemiological studies suggesting that they may have a protective role in conditions such as cardiovascular disease.
Cancer
In vitro studies have demonstrated that the initiation stage of cancer can be prevented by the action of tea flavonoids
Tea polyphenols have been shown to inhibit DNA synthesis of leukaemia cells and lung carcinoma cells
Animal studies have shown that tea and its flavonoids protects against many types of cancer e.g. skin tumors in mice, lung cancer in mice and digestive cancer in mice and rats
Antibacterial effects
Tea extracts exhibit inhibitory effects against Salmonella typhi, Campilobacter jejuni, Campilobacter coli, Helicobacter pylori, Shigella, Clostridium, Pseudomonas, Candida and others
Dental Caries
Green tea and various catechins have exhibited inhibitory effects on the growth of cariogenic bacteria by preventing the adherence and growth of bacteria at the tooth surface
Absorption of tea flavonoids
Until recently the majority of the research demonstrating the antioxidant activity of tea flavonoids was either using animal models or laboratory cellular studies. Emerging evidence is concluding that the body does in fact absorb some of these antioxidants, e.g. when green tea extract is consumed by healthy human volunteers, various catechins are found in the plasma in a dose-dependent concentration varying between 0.2-2.0% of the ingested amount, with a maximum concentration being achieved 1.4 to 2.4 hours after consumption. Some studies have shown that plasma antioxidant activity peaks 30-60 minutes after tea consumption and returns close to baseline by 90 minutes. Further research is currently being undertaken on the metabolism, distribution and excretion of tea flavonoids and its metabolites.
The addition of milk to tea, as enjoyed by the majority of the UK population, does not appear to affect the bioavailabilty of the tea flavonoids.
In summary.
It is well known that fruit and vegetables are good sources of antioxidants, however, what is less well known is the amount of antioxidants present in tea. The major group of antioxidants in tea are flavonoids that appear to be digested, absorbed and metabolised by the body. There is a wealth of evidence demonstrating that tea and flavonoids exhibit beneficial effects in animal and in vitro studies and provide a promising area of research for future human studies.
So as well as eating more fruit and vegetables, antioxidant intake can be topped up by drinking more tea, helping to promote overall health and well-being.
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Tea and Cardiovascular Disease
Introduction
Cardiovascular Disease (CVD) is the main cause of death in the UK, accounting for over 250,000 deaths a year, more than one in three people. The main forms of CVD are Coronary Heart Disease (CHD) and stroke. About half of all deaths from CVD are from CHD and about a quarter are from stroke. More than 110,000 people die of heart problems, 300,000 have heart attacks and 1.4 million suffer from angina every year. In addition, CHD accounts for about 3% of all hospital admissions in England.
Risk Factors associated with CHD
There is no one single cause for CHD, instead the risk of developing it is determined by a combination of factors, some of which are unalterable, others that are potentially modifiable. These risk factors are outlined in Table 1.
Table 1
Modifiable Risk Factors Non-modifiable risk factors
Hyperlipidaemia (raised cholesterol and triglycerides)
Hypertension (high blood pressure)
Reduced physical activity
Smoking
Stress
Obesity Family history
Sex
Age
Other physiological factors and conditions that may increase the risk of developing CHD, include:-
Insulin resistance syndrome
Oxidation of lipoproteins
Inflammation and endothelial damage
Hyperhomocysteinaemia (high blood homocysteine)
Platelet aggregation
Clotting factors
Diabetes Mellitus
Renal Disease
Prevention
Primary prevention of CVD involves adopting a 'healthy lifestyle' to control the 'modifiable' risk factors. The important aspects of this type of lifestyle include:-
Quitting smoking
Taking regular exercise
Adopting a healthy diet
Reducing stress and anxiety levels
Dietary Recommendations
A healthy diet3 that includes the following;-
Increasing the consumption of oily fish
Increasing fruit, vegetable and pulses
Replacing some of the dietary energy coming from total fat with complex starchy foods
Moderating fat reduction with the use of monounsaturated fats
Limiting salt intake
Consuming modest amounts of alcohol
can help to reduce the risk of CVD by altering a range of risk factors in a number of ways. Some of these effects are outlined in Table 2.
Table 24
Dietary Intervention Physiological Effect
Omega 3 fatty acids (oily fish, rapeseed oil) Anti-inflammatory, protecting against endothelial damage
Anti-thrombotic
Reduces triglycerides
Improves insulin sensitivity
Anti-arrhythmic effects
Other fatty acids Action of omega-3 fatty acids is improved by lower intakes of saturated fat
Lower saturated fats reduces the risk of thrombosis and reduces serum lipids
Fruit, vegetables, pulses, nuts Antioxidants protect against Low Density Lipoprotein (LDL) oxidation
Rich in potassium, may help to control blood pressure
Rich in folic acid, may prevent homocysteine formation
Contain soluble fibre, helping to improve lipid profiles
Alcohol Improved HDL levels
Possible antioxidant effects
The benefits of tea
There is growing evidence suggesting that other dietary components may enhance the general healthy eating recommendations. For example, research is highlighting that there maybe a beneficial relationship between tea drinking and reduced risk of cardiovascular disease.
The evidence for tea and CVD
A number of epidemiological studies have demonstrated that total flavonol/ flavonoid or tea consumption is linked to protection from heart disease and stroke. However, not all studies have shown similar protective effects. Inconsistencies from these studies maybe as a result of their design e.g. lack of detail about exposure to tea - quantity, strength and variety, insufficient information about the flavonoid contents of foods and other risk factors for CVD not being considered. These details may influence the end results and consideration of these factors is required for any future research.
However, the conclusions from a recent meta-analysis of all studies investigating the relationship between tea drinking and CHD suggested that drinking 3 cups of tea a day reduces the risk of myocardial infarction by 11%.
Protective mechanisms of tea
The outcomes from these studies have created great interest in understanding the mechanisms by which tea may confer its cardiovascular protective properties. Mechanisms such as the prevention of LDL oxidation , reduction in blood lipids24-26, anti-inflammatory actions, improvements in blood vessel function and inhibition of platelet aggregation have been established mainly in animal and in vitro studies. These mechanisms are discussed in greater detail in the fact sheet 'Tea and Antioxidants'.
Results in human studies are not as clear, and although some epidemiological studies seem to indicate that tea can reduce serum cholesterol8, , most studies show no effect in reducing serum cholesterol or blood pressure. As antioxidant activity from tea has been demonstrated in vivo , it may be that tea exerts its cardioprotective properties in other ways such as improvements in endothelial dysfunction, platelet aggregation 34 or ways that have yet to be investigated.
In summary
From a number of epidemiological studies investigating the relationship between tea drinking and cardiovascular disease, it is reasonable to conclude that drinking both green and black tea is compatible with dietary advice to help protect against CVD. However, although the scientific evidence for the mechanisms by which tea exerts its positive health effects is growing, it is not yet conclusive and represents promising areas for future research in human trials.
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Tea and Cancer
Introduction
Cancer is a major cause of morbidity in the UK with over 200,000 newly diagnosed cases, and around 120,000 deaths from cancer each year. It is expected that more than one in three people in England will develop cancer at some stage in their lives1. The disease is more likely to develop in later life, with around 65% of cancers diagnosed in people over the age of 65. However, cancer causes an even greater proportion of deaths in those under the age of 65, with more than one in three deaths being due to cancer.
What is cancer?
Cancer is often thought of as a single disease; however in reality it is a term that covers a range of malignant conditions that can affect almost any organ or tissue in the body. Cancer occurs when tissue cells are no longer under the control of normal molecular regulatory processes that usually result in the division, differentiation and ultimately death of these healthy cells. When these control mechanisms become disturbed the cells divide in an uncontrolled and abnormal manner, often failing to differentiate and failing to respond to the usual death signals. In most cancers this uncontrolled growth results in the formation of a tumour.
In many cancers the malignant cells will migrate from their primary tissue of origin to secondary sites creating secondary tumour growths or 'metastases'. The lethal effects of both primary and secondary cancers is due to the compression of healthy cells, often killing them, so preventing the normal functioning of major organs.
Causes of cancer
Cancer is essentially a disorder of cellular genetic material. Damage to the DNA within the cells maybe as a result of environmental factors such as radiation, chemical carcinogens and some viruses.
Certain risk factors are associated with different types of cancer, and some of these are modifiable3:-
Smoking is the greatest known risk factor for cancer and has been identified as the single most important cause of preventable disease and premature death in the UK
UV (Ultraviolet) Radiation, specifically UVA and UVB, cause skin damage, including sunburn and premature ageing of the skin. This damage can eventually lead to skin cancer
Diet, scientists at the Imperial Cancer Research Fund have estimated that 30% of all cancers may occur as a result of our diet
Obesity may increase an individual's risk of developing certain types of cancer e.g. endometrial, breast, kidney and bowel cancers
Excessive alcohol consumption strongly increases an individual's risk of developing oral cancer, laryngeal cancer, and oesophageal cancer
Occupational hazards, exposure to certain chemicals has been to shown to be a risk factor for certain cancers
Diet and cancer
More and more research is finding that diet plays a crucial role in the prevention of cancer. The International Report on cancer prevention from the World Cancer Research Fund, Food, Nutrition and the Prevention of Cancer: a global perspective, found that 30-40% of all cancers are directly linked to our diet, physical activity and weight. Diet is thought to be a risk factor for the following cancers.
Bowel cancer - eating foods that are high in fat and low in fibre may increase the risk of developing bowel cancer.
Breast cancer - maybe a link between fat consumption and breast cancer risk although this link remains uncertain.
Stomach cancer - a high intake of salted, cured, and smoked foods may be linked with an increased risk of developing stomach cancer.
Prostate cancer - many studies have been carried out looking at links between diet and prostate cancer. Although many links have been suggested, no definite links can be consistently found.
Lung cancer - a low consumption of fruit and vegetables (in particular green vegetables and carrots) has been shown to be associated with an increased risk of developing lung cancer.
Oesophageal cancer - diets that are low in fruits and vegetables may increase the risk of developing oesophageal cancer.
Findings from the world's largest investigation into diet and cancer, EPIC (European Prospective Investigation into Cancer and Nutrition), monitoring 480,000 individuals, have found that eating about 500g or more fruit and vegetables every day was found to decrease the number of cases of cancers of the mouth, pharynx and oesophagus by 50%.
Dietary Recommendations
The World Cancer Research Fund5 has made the following dietary recommendations:-
Increase fruit and vegetable intake - at least 5 portions per day (a portion is approximately 120 grams or 4 ounces).
Consume a high proportion of high fibre foods such as wholemeal bread and other cereals
Choose a variety of plant based foods such as cereals, legumes (such as lentils, beans and peas), starchy foods (such as pasta, rice and bread) as well fruit and vegetables
Select foods low in fat and salt
Drink alcohol in moderation if at all
These dietary changes as well as maintaining a healthy weight and being physically active can help reduce the risk of developing cancer.
The Committee on Medical Aspects of Food and Nutrition policy (COMA6) assembled a working party of experts to look at the evidence for the role of nutrition in cancer causation and to develop recommendations for the prevention of a number of common cancers. In addition to the above dietary recommendations they also suggested that red meat and processed meat consumption should not increase, instead choosing white meat and fish as alternatives
The Benefits of Tea
There is increasing evidence that specific substances found in certain foods can enhance general healthy eating recommendations e.g. phenolic compounds found in plants. Tea is rich in specific phenolic compounds including flavonoids.
Flavonoids are powerful antioxidants in vitro and have been identified as potential cancer preventatitive components.7-10 Tea has been shown to inhibit tumorigenesis at the initiation, promotion and progression stages of cancer. It has been suggested that possible mechanisms of action include their:
Antioxidant activity
Ability to inhibit nitrosamine reactions1
Modulation of carcinogen-metabolising enzymes
Trapping of ultimate carcinogens
Ability to inhibit cell-proliferation
Modulation of gut-microflora18 (associated with colon cancer)
Antimicrobial actions (association between Helicobacter pylori and gastric cancer)
For further information about the antioxidant action of tea please refer to the fact sheet, 'Tea and Antioxidant Properties.'
The evidence for tea and cancer
In a Japanese population survey, an overall protection together with a slowdown in increase of cancer incidence was reported with tea drinking. The effects were more pronounced when the consumption rose to over 10 cups of tea a day. However, other epidemiological studies investigating the association between tea consumption and a reduced risk of cancer have been inconclusive.
Some studies have shown an inverse association between green tea drinking and stomach cancer, one of which reported that green tea drinkers had a 48% reduced risk of developing stomach cancer and a 51% lower risk of developing chronic gastritis versus non drinkers. However, one study in Taiwan showed an increased risk with green tea drinking and other studies investigating the relationship between flavonol intake and stomach cancer reported no association.
Flavonoids have also been associated with a reduced risk of lung cancer and one case control study reported a 50% reduction in lung cancer risk when consuming 1 cup of black tea a day. However, another study that investigated the relationship between catechin intake (a type of flavonoid that is abundant in tea) and lung cancer, found no such association34. Other studies investigating the relationship between tea drinking and lung cancer also reported no association.
Results from a recent study in Japan found that the regular consumption of green tea (more than 3 cups a day) might be protective against recurrence of breast cancer in the early stages, although the authors do report that careful interpretation of the results is needed at this stage and further studies are required to confirm these findings.
Inconsistencies from these studies maybe as a result of their design e.g. lack of detail about exposure to tea - quantity, strength and variety, insufficient information about the flavonoid contents of foods, variation of flavonoid content amongst food varieties, discrepancies in the collation of dietary information using dietary analysis questionnaires and confounding lifestyle and environmental factors. These details may influence the end results and make them difficult to interpret. This problem has been reviewed in association with cancer and tea drinking. Consideration of these factors is required for any future research.
In summary
1. Tea and flavonoids have been identified as potential cancer preventatitive components in animal and in vitro studies. However, the inconclusive results reported in population studies maybe as a result of a number of confounding factors making the results difficult to interpret. Although the scientific evidence for tea is growing it is not yet conclusive and represents a promising area for future research. In the mean time, it is reasonable to conclude that drinking both green and black tea is compatible with healthy eating dietary advice to help reduce the risk of developing cancer helping to maintain overall health and well-being.
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Tea and Hydration
Introduction
The Tea Council's Healthy Drinks Survey revealed that a third of all adults in the UK are not meeting their fluid requirements by failing to replace the fluid that is lost daily by their bodies. Fluid is vital to life, and whilst humans can survive weeks without food, they can only survive a few days without fluid. It is vital for a number of bodily functions including:
Transportation for essential nutrients and oxygen (blood)
Excretion of waste products (urine and faeces)
Lubrication (joints and eyes)
Regulation of body temperature
As a result, maintenance of an optimal fluid balance is important for general health and well being.
Body Fluid
Approximately 50-70% of our body weight is made up of water, which varies depending on age (higher in infants than adults) and gender (lower in women than men due to a higher composition of body fat containing no water). This fluid is distributed amongst the extracellular (blood and other fluids) and intracellular (within the cells) compartments of the body.
Fluid Balance
Fluid balance is based on:
the amount of water that is lost in the urine, faeces, skin and lungs and
the intake of water coming from food, drinks and metabolism.
Table 1 shows the water balance of a sedentary individual with a body weight of 70-75kg living in a temperate climate.1
Table 11
Water (ml/day)
Intake
Food
Drinks
Metabolism
Output
Urine
Faeces
Skin
Lungs
1000ml
1200ml
350ml
2550ml
1250ml
100ml
850ml
350ml
2550ml
The regulation of this fluid balance is very tightly controlled by various homeostatic mechanisms e.g. a water deficiency causes a fall in blood volume and consequently an increase in osmolality of all body fluids, which stimulates the thirst centre and the osmoreceptor in the brain. This results in thirst (leading to conscious drinking behaviour) and the release of the antidiuretic hormone vasopressin (acts on receptors in the kidney to increase water absorption and reduce urinary volume). When the body contains an excess of water the reverse occurs.
Fluid Depletion
The tight regulation of the body's fluid balance generally results in variations of total body fluid levels of less than 1%. However, changes as little as 1-2% can result in dehydration.
Chronic dehydration may occur in situations where there is a continual low intake of fluid and particular populations at risk include
Children - maybe less aware of the need of increased drinking and have a relatively insensitive thirst mechanism
The elderly - possibly due to a reduced thirst response3, chronic physical and/ or mental impairment
The effects of chronic dehydration include constipation, lethargy, headaches, mental confusion (in the elderly), increased risk of urinary tract infections and renal stones. In addition, there does appear to be some evidence of a link between a habitually low fluid intake and certain cancers eg colon and breast.
Acute dehydration may be as a result of increased fluid losses such as
Diarrhoea and vomiting
Pyrexia
Burns
Undiagnosed Diabetes Mellitus
Prolonged use of diuretic drugs
Physical activity
Severe dehydration is associated with compromised cardiovascular function, renal impairment, weakness and lethargy, headaches and nausea.
Fluid Requirements
Individual requirements for fluid vary considerably as the amount of fluid lost will depend on various factors such as the environmental temperature, humidity, individual metabolism, activity levels, general state of an individual's health and diet.
However, as a general rule most healthy adults should aim for a daily intake of 35ml of fluid per kg body weight per day and the British Dietetic Association recommends that most healthy adults should drink at least 1.5-2.0 litres of liquid every day (more in hot weather and if physically active).
Unfortunately the thirst mechanism is rather insensitive in humans and so thirst should not be relied on as the main stimulus or reminder to drink, and for this reason it is important to maintain fluid intake throughout the day.
Tea and fluid replacement
In the past it has been widely believed that tea should be avoided as a fluid replacement due to the diuretic action of the caffeine present.
An extensive review of the medical and scientific literature , carried out by Professor Ron Maughan and Jane Griffen, concluded that 'there is no evidence base for the assumption that all caffeine containing drinks should be avoided in situations where fluid balance is, or might become, precarious.' It was found that tea does not have a diuretic effect due to caffeine unless the amount of tea consumed at one sitting contains more than 250-300mg of caffeine, equivalent to between 5 and 6 cups of tea.
In fact, due to the volume of fluid that is drunk whilst enjoying a cup of tea, the British Dietetic Association advises that tea can contribute towards the daily-recommended fluid intake of 1.5 to 2 litres.
In Summary.
About 70% of the UK population drink tea on a regular basis, drinking on average three to four cups of tea a day. At this intake tea can make a positive contribution to the body's hydration status, helping to promote health and well being.
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Tea and Oral Health
Introduction
Dental disease remains a significant problem in the UK with the vast majority of the population suffering with the consequences of this disease at some stage in their lives. It can result in acute pain, aesthetic problems and can increase the risk of tooth loss, which may have long-term effects on food intake resulting in impaired nutritional status and subsequent overall well being.
Damage to or loss of teeth may result from:-
Dental caries
Acid erosion
Periodontal disease
Dental Caries
Caries is caused by bacterial acid production in tooth plaque, which can cause deep localized lesions if it remains too near the tooth for any length of time. If left the bacteria then may penetrate the tooth further and progress into the soft pulp tissue. Untreated dental caries can lead to incapacitating pain, potential tooth loss and loss of dental function. The development and progression of dental caries is due to a number of factors, specifically bacteria in the dental plaque (particularly Streptococcus mutans and lactobacilli) on susceptible tooth surfaces and the availability of fermentable carbohydrates.
The prevalence of dental decay in children in the UK has fallen significantly since the 1970's mainly as a result of the introduction of fluoridated toothpaste and fluoridation of water supplies. Nevertheless dental caries still remains a significant problem.1
Acid Erosion
The damage to teeth from acid erosion is now thought to be a significant contributor to dental disease.Erosion arises from acid derived from foods and drinks, or regurgitations from the stomach, which repeatedly wash over the teeth and result in shallower but more widespread lesions.
Periodontal Disease
Periodontal disease results from inflammation of the gum (gingivitis) that gradually causes destruction of the bone supporting the teeth. Gingivitis usually results from infection from debris that has accumulated at crevices at the base of the teeth.
Although the main reason for tooth extraction is as a result of dental caries, there appears to be an increasing trend for tooth loss in adulthood resulting from periodontal disease. The Adult Dental Survey found that about 95% of the UK population had some signs of gum disease.
Prevention of Dental Disease
Good oral hygiene practices - including proper cleaning of the teeth and gums to remove plaque build up and accumulation of debris at the base of the teeth
Fluoride Protection - fluoride is incorporated into tooth enamel making it harder and more resistant to acid attack. As well as fluoride containing toothpastes, the fluoride content of drinking water is also an important factor, and caries prevalence is lower where water is naturally or artificially high. It is believed that water fluoridation is the most effective public health strategy for caries prevention. However, there are wide variations in the levels of fluoride naturally occurring in fresh water ranging from 0.01 to 100 ppm and only about 10% of the water in the UK is fluoridated at the 'optimal' level of 1ppm.
Dietary measures including:
Reducing the frequency of consumption of sugar containing foods and drinks
Consuming acidic drinks only at meal times. Between meal drinks should be non-acidic. reducing the frequency of consumption sugar containing foods and drinks Consuming acidic only at meal times. Between should be non-acidic.
Tea and Dental Health
Epidemiological surveys have reported that some populations who drink tea on a regular basis have a reduced number of carious teeth Proposed mechanisms for tea's oral health benefits include:-
1. Fluoride
The tea plant (Camellia Sinensis) extracts fluoride from the soil, which then accumulates in its leaves. For this reason tea is a very rich source of fluoride;
dry tea leaves may contain 4-400ppm fluoride, the brewed tea 0.34-6ppm resulting in one cup of tea containing between 0.3mg and 0.5mg of fluoride. In fact, in the UK the majority of fluoride comes from tea, providing 70% of our daily intake.
Findings from a recent study that investigated the bio-availability of fluoride from tea in relation to its interaction with the tooth surface and oral tissues,14 demonstrated that after rinsing with tea, 34% of the fluoride was retained in the oral cavity and that some of this showed a strong binding ability to enamel particles on the tooth surface. For this reason the authors concluded that tea was an effective vehicle for delivering fluoride to the oral cavity where it may then become associated with the oral tissues potentially helping to prevent dental decay.
Some concern has been raised over excessive intakes of fluoride causing fluorosis in the enamel of the teeth while it is still forming in children. Early signs of fluorosis are mottling and discoloration of the teeth. Although appearance of the teeth is affected, the structure of the teeth will actually be stronger and less likely to get decay. In addition, the Dental profession is almost totally in favour of water fluoridation and any concerns have been carefully considered and discounted by the Public Health Alliance and the British Fluoridation Society (1995).
2. Tannins
Other components of tea may also contribute to the inhibition of caries. It has been reported that the tannins in tea can inhibit salivary amylase thereby reducing the cariogenic potential of starch-containing foods. A number of studies have also demonstrated that tannic acid inhibits the growth of S.mutans bacteria,16-20 a major factor in the build-up of dental plaque.
3. Acid erosion
In addition to its beneficial effect on plaque, tannin, along with other components of tea such as catechin, caffeine and tocopherol have been shown to be effective in increasing the acid resistance of tooth enamel. Their effects increased dramatically when they were used in combination with fluoride.
The acid content of black tea and its influence on oral acidity during consumption has also been investigated. The pH of the tooth surface in ten healthy volunteers was examined after consuming black tea. The very small, short-lived, pH decrease that was observed led to the conclusion that tea can be recommended as an alternative drink to the more acidic versions, such as fizzy drinks, as part of preventive measures for dental erosion.
4. Flavonoids
Green tea and specific flavonoids, mainly catechins, have exhibited inhibitory effects on the growth of cariogenic bacteria by inhibiting the adherence and growth of plaque bacteria at the tooth surface.
Tea and Oral Cancer
Preliminary results from trials determining the role of tea in the prevention of oral cancer look promising. One double-blind, randomised intervention trial suggested that treating patients with a mixture of black and green tea components could improve the clinical manifestations of their oral lesions.
In Summary.
There is a growing amount of in-vitro research identifying tea's potential oral health benefits. Although the scientific evidence for the mechanisms by which tea exerts its positive health effects is not yet conclusive it represents promising areas for future research in human trials. In the mean time it is reasonable to conclude that drinking tea, without the addition of sugar, is compatible with dietary advice to prevent dental decay, thereby helping to promote overall health and well being.
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About Tea
There are more than 3,000 varieties of tea, each with its own flavour, body, colour and aroma. Like wines, they take their names from the districts where they are grown. While there is only one species of tea plant, Camellia Sinensis, from which all teas are made, local conditions in the various tea-growing regions of the world produce varieties, which are unique from each other. The major tea producing countries include India, China, Taiwan (Formosa), Sri Lanka (Ceylon), Japan, and Africa.
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Different Types of Tea
How is black Tea Graded?
After the tea leaves are crushed, fired and dried, they pass through screens for grading. Tea leaves vary in size and are sorted by the size of the leaf. The grade designates leaf size only, not quality.
There are four grades. The main division is between "leaf" grade and "broken" grade. Teas designated OP-Orange Pekoe (pronounced peck-o) are comprised of whole leaves that are classified by size. BOP-Broken Orange Pekoe designates a high quality grade of leaves that have been broken, either deliberately or not. A lesser quality grade of very small pieces is called "fannings." Finally, "dust" grades are used primarily in tea bags.
In addition to the grading process, the tea industry classifies tea leaves from where on the tea plant they were plucked, and also what time of year the harvest took place. A "fine picking" is comprised of the top "two leaves and a bud" of the tea plant. The "bud" is the immature leaf tip. Early in the growing season the young tips have a golden color. Teas produced at this time are referred to as Golden Flowery Orange Pekoe-GFOP. When the number of golden tips is relatively high, the designation of TGFOP is used, indicating Tippy GFOP. Indian teas are occasionally designated FTGFOP1 for Finest TGFOP, grade 1 and SFTGFOP1 for Super-Fine TGFOP, grade 1 or "I" for Imperial grade.
How much caffeine does tea have?
A cup of black tea, brewed for five minutes, contains one-third as much caffeine as a cup of coffee. This information is provided by Kaiser Permanente, Department of Nutritional Services study, 1986.
Are there any teas which are caffeine-free?
Our decaffeinated teas are processed using pure carbon dioxide. This method removes 99% of the caffeine content and leaves no residual chemicals. Tisanes and herbal blends do not contain any tea leaves (therefore there's no caffeine). We have a wonderfully aromatic selection of tisanes and herbal blends. Tisanes are made from pieces of dried fruit and flowers. Come in and ask to smell the fruity tisanes -- they will delight your senses.
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Black and Green Tea: How do they differ?
Introduction
Both green tea and black tea come from the leaves of the plant Camellia sinensis, however the processing that the leaves undergo to make the final tea is different. The leaves for black tea are fully oxidised while those for green teas are lightly steamed before being dried. Figure 1 outlines the processing of green and black tea in more detail.
Figure 1 - Green and Black Tea Processing
Black teas mostly come from plantations in Africa, India, Sri Lanka and Indonesia while green teas come from countries in the Far East such as China and Japan.
Flavonoid content of black and green teas
Black and green teas both contain similar amount of flavonoids however they differ in their chemical structure. Green teas contain more of the simple flavonoids called catechins, while the oxidisation that the leaves undergo to make black tea converts these simple flavonoids to the more complex varieties called theaflavins and thearubigins. Table 2 provides average values for the different flavonoids present in green and black tea although they will differ dependent on the variety of leaf, growing environment, manufacturing, particle size of ground tea leaves and infusion preparation.
Table 2 - Flavonoids in green and black tea3
Flavonoids
Green Tea (average/ 100g)
Black Tea (average/ 100g)
Catechins 14.2g 4.0g
Theaflavins - 0.94
Flavonol glycosides 0.64 0.47
Flavone C glycosides 0.086 0.051
TOTAL POLYPHENOLS* 16.0 15.6
* Majority of polyphenols in tea are flavonoids Oolong tea, is a partially fermented leaf, with a flavonoid profile midway between green and black tea.
The health benefits of flavonoids
Although the oxidisation process modifies the type of flavonoids present, the total level and their overall antioxidant activity, is similar in both teas4. Research is now suggesting that antioxidants, such as those found in both green and black tea, may have a protective role to play in certain conditions such as heart disease, stroke and some cancers. Further information about the health benefits of black tea, antioxidants and flavonoids can be found in the Fact Sheets 'Tea and Antioxidants; Tea and Cancer; Tea and Cardiovascular Disease'.
The health benefits of green tea
Green tea specifically has been associated with protection against certain types of cancer5,6 including lung7, stomach cancer8-14 and its precancerous condition, gastritis8,15. Moreover, an observational study in Japan found that the regular consumption of green tea (more than 3 cups a day) might be protective against recurrence of breast cancer in the early stages.
The possible protective mechanism of green tea is unclear, although a number of in vitro and animal studies are attempting to explain this, including a study that found that the green tea polyphenol (-) -epigallocatechin (EGC) inhibited the DNA replication in leukaemia cells, resulting in the death of these cells. Other mechanisms by which green tea may be protective is discussed in more detail in the fact sheet 'Tea and Cancer.'
Further work is still required in understanding the protective antioxidant action of black and green teas. In one in vitro study, black tea was found to be more efficient than green tea as a chemopreventor against certain free radicals, oxygen and nitrogen species. However, in another study both green tea and black tea were equally able to protect against Nitric Oxide toxicity.
In addition to its potential anticarcinogenic and antioxidant effects, other studies have shown green tea to have anti-inflammatory, antithrombotic, cholesterol lowering, antiviral and antibacterial properties.
Although the scientific evidence demonstrating the health benefits of green tea is increasing it is not yet conclusive and provides an interesting area for future research.
Green tea and skin protection
A number of animal studies have shown that topical treatment or oral consumption of green tea polyphenols, inhibit chemical carcinogen or ultraviolet radiation-induced skin tumours in different animal models. Treatment of green tea polyphenols to skin has been shown to have a beneficial effect on the biochemical pathways involved in skin inflammation, cell proliferation and chemical tumour promoters. These results have been confirmed in a human model, where topical application of green tea polyphenols protected against UV light induced DNA damage. Based on results mainly from animal studies, many companies are now supplementing their skin care products with green tea extracts. However, the effects on human skin are still not well understood and further research in this field is required.
Green tea extract and weight loss
Preliminary research published in the American Journal of Clinical Nutrition suggests that an extract from green tea may help with weight loss by speeding up fat oxidation. In this study, researchers conducted a 6 week study of 10 healthy men in their 20's and found that those men who were given a green tea extract used more calories in a day than those who did not. Further research is required before any firm conclusions about green tea and weight loss can be drawn.
Caffeine Content of Green Tea and Black Tea
Black and Green teas are produced from the same plant Camellia sinensis so both green and black tea naturally contain caffeine. Further information about caffeine and tea can be found in the Fact Sheet, 'Caffeine: The Facts'.
Which to drink?
The health benefits gained from drinking black and green tea are comparable, both helping towards promoting health and well-being. The decision about which to drink is simply a matter of taste.
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The Nutritional Value of Tea
Introduction
On average, British people drink approximately 3 cups of tea a day with about 70% of the UK population drinking tea on a regular basis1. On-going research is discovering that at this level of intake tea may offer significant health benefits.
In addition to tea's contribution to overall daily fluid intake as well as the presence of powerful antioxidants called flavonoids, tea, when taken with milk, may also contribute to our daily intake of certain nutrients. For further information about fluid and antioxidants, please refer to the fact sheets, 'Tea and Hydration' and 'Tea and Antioxidant Properties'
Nutritional Value of Tea
Taken on it's own tea has no calories. However, when milk is added to it, as enjoyed by 98% of the population, it can provide a number of vitamins and minerals. Table One lists the nutrients present in 3 cups of tea, along with the added semi-skimmed milk, as well as their overall contribution to recommended daily intakes and their main functions.
In addition to the nutrients described in table 1, tea provides 70% of our daily Fluoride intake.2 Fluoride is needed to support bone mineralisation and protect teeth against dental caries.
In Summary.
As well as contributing to fluid and antioxidant intake, drinking 3-4 cups of tea a day with milk, can provide certain vitamins and minerals, thereby helping to support overall health and well being.
Table One
NUTRIENT3 Amount provided by 3 cups of tea ALONE* Percentage of DAILY Recommended Nutrient Intake PROVIDED BY TEA ALONE***4 AMOUNT PROVIDED BY THE semi-skimmed milk PRESENT IN 3 CUPS OF TEA** Percentage of DAILY Recommended Nutrient Intake PROVIDED BY the milk ALONE IN 3 CUPS OF TEA***4 TOTAL Amount provided by 3 cups of tea* with semi-skimmed milk
Minerals:
Calcium
Zinc
Potassium
Manganese
Trace
Trace
97 mg
0.8mg -
-
3%
- 108 mg
0.36 mg
135mg
- 15%
5% (Females), 4% (Males)
4%
- 108 mg
0.36 mg
232 mg
0.8mg
Vitamins:
Thiamin (B1)
Riboflavin (B2)
Vitamin (B6)
Folate
Niacin
Pantothenate
Vitamin B12 -
Trace
57 mcg
-
Trace
Trace
0.57mg
Trace
Nil -
5% (Females), 4% (Males)
-
-
4% (Females), 3% (Males)
-
- 36 mcg
162mcg
54mcg
5.4 mcg
0.09mg
0.3mg
0.36mcg 5% (Females), 4% (Males)
15% (Females), 13% (Males)
5% (Females), 4% (Males)
3%
1% (Females), 1% (Males)
-
24% 36 mcg
219 mcg
54mcg
5.4 mcg
0.66mg
0.3mg
0.36mcg
Nutritional Value of 3 cups of tea and the milk present in 3 cups of tea
Notes:
*1 cup = 190ml5 **Portion of milk in 1 cup = 30ml5
*1 cup of milked tea contains 190ml tea and 30ml milk
*** Based on recommended intake for 19-50 year olds (see Table Two)
MAIN FUNCTIONS
Calcium is vital for the formation of bones and teeth. It also has a role at the cellular level where it is important for activities such as muscle contraction, blood clotting and nerve transmission
Zinc is present in many enzymes and is required for growth, tissue repair and for sexual maturation
Potassium is important in the regulation of fluid balance as well as for the proper functioning of cells, including nerves and muscles
Manganese is essential for the development of enzymes, as well as being an important component for bone and cartilage
Thiamin is needed to release energy from carbohydrate
Riboflavin is required to release energy from protein, carbohydrate and fat
Vitamin B6 is involved in the metabolism of protein. Vitamin B6 dependent enzymes are also involved in the metabolism of glycogen and lipids and the synthesis of haem
Folate is essential for the synthesis of DNA and therefore plays a crucial role in cell division as well as the formation of blood cells
Niacin is involved in the release of energy in tissues and cells
Pantothenate plays a central role in energy metabolism
Vitamin B12 is necessary for the proper formation of blood cells and nerve fibres
Main Functions of Some of the Nutrients present in tea and milk
Table Two
NUTRIENT RNI's FOR COMPARISON TO TEA
*RNI = Reference Nutrient Intake
** EAR = Estimated Average Requirements
Nutrient RNI
(19-50 year olds) RNI
(50+ year olds)
Energy (kcal)** 1940 (females)
2550 (males) 1900 (females)
2550 (males)
Protein (g)* 45 (females)
55.5 (males) 46.5 females
53.3 (males)
Fat (g) 33% of energy 33% of energy
Carbohydrate (g) 47% of energy 47% of energy
MINERALS
Calcium (mg) 700 700
Zinc (mg) 7 (females)
9.5 (males) 7 (females)
9.5 (males)
Potassium (mg) 3,500 3,500
Manganese (mg) NA NA
VITAMINS
Vit B2 (mg) 1.1 (females)
1.3 (males) 1.1 (females)
1.3 (males)
Vit B1 (mg) 0.8 (females)
1.0 (males) 0.8 (females)
0.9 (males)
Vit B6 (mg) 1.2 (females)
1.4 (males) 1.2 (females)
1.4 (males)
Folate (mcg) 200 200
Carotene NA NA
Niacin (mg) 13 (females)
17 (males) 12 (females)
16 (males)
Pantothenate (mg) NA NA
Vitamin B12 (mcg) 1.5 1.5
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Tea and Caffeine
What is caffeine?
People have enjoyed caffeinated beverages for many years Caffeine is a naturally occurring substance found in the leaves, seeds or fruits of at least 100 different species worldwide and is part of a group of compounds known as methylxanthines. The most commonly known sources of caffeine are coffee, cocoa beans, cola nuts and tea leaves. Caffeine is also added to specifically formulated 'energy drinks' and pharmaceutical products such as cold and flu remedies.
Coffee and tea also contain other dimethylxanthines; theophylline which has similar properties to caffeine and theobromine whose pharmacological actions is far less potent than caffeine and theophylline.
The amount of caffeine present in products depends on the type of the product, the serving size and the preparation method. For example a 190ml cup of tea contains 50mg of caffeine, one third less than the same amount of an instant cup of coffee (75mg). Table 1 gives an indication of the amount of caffeine found in other drinks compared to tea:
Table 1
Type of Product Caffeine (mg/ serving)
Tea All types 50mg/ 190ml serving1
Coffee Brewed (filter or percolated) 100-115mg/ 190ml serving1
Instant 75mg/ 190ml serving1
Cola drinks Standard and Sugar Free 11-70mg/ 330 ml can2
'Energy' drinks All types 28-87mg/ 250ml serving2
Chocolate Bar 5.5-35.5mg/ 50g bar2
On average we consume 3.98mg of caffeine /kg body weight per day ie 239mg/ day for a 60kg person3.
What is a safe intake of caffeine?
Up to 300mg/day (6 cups of tea) is considered moderate, with no evidence of harmful effects in the vast majority of the adult population. Some individuals are sensitive to caffeine and will feel effects at smaller doses than other individuals who are less sensitive. For this reason, these individuals may need to limit their caffeine intake.
Metabolism and Clearance
Caffeine does not accumulate in the body over a course of time and is normally excreted within several hours of consumption. The rate of caffeine elimination varies between individuals and this maybe as a result of genetic factors affecting the enzymes involved in the metabolism, or due to certain lifestyle factors eg smoking. Children also metabolise caffeine at a quicker rate. Generally caffeine absorption is complete within about one hour after ingestion and the plasma concentration peaks after about 60-90 minutes. The half-life of caffeine in the plasma is about 2.5 - 4.5 hours in healthy adults.4
Caffeine Tolerance
A number of different factors affect individual tolerance to caffeine, including the amount ingested, the frequency of caffeine consumption and individual metabolism. It is widely recognised that gradual tolerance develops with prolonged caffeine use.
Physiological Effects
Caffeine is a pharmacologically active substance, and depending on the dose, has a number of actions:-
Central Nervous System Stimulant. A moderate caffeine intake can cause mild stimulation that maybe beneficial in terms of increased alertness, concentration, improved performance and decreased fatigue.5-10 However, higher intakes may affect sleep, cause nervousness and an irregular heartbeat.
Weak Bronchodilator. As a result, interest has been shown in its potential role as an asthma treatment. A number of studies have explored the effects of caffeine in asthma and the conclusions from a Cochrane Review suggest that caffeine appears to improve airways function modestly in people with asthma for up to four hours after consumption.11
Diuretic. The diuretic action of caffeine may be due to an increase in renal blood flow, leading to an increased glomerular filtration rate (GFR), or due to a decreased reabsorption of sodium in the renal tubules. The diuretic effect of caffeine is dependent on the amount consumed and duration of intake eg the caffeine in tea does not have a diuretic effect unless the amount of tea consumed at one sitting contains more than 250-300mg of caffeine, equivalent to between 5 and 6 cups of tea.
In fact, due to the volume of fluid that is drunk whilst enjoying a cup of tea, the British Dietetic Association advises that tea can contribute towards the daily-recommended fluid intake of 1.5 to 2 litres.
Cardiac Muscle Stimulant. Moderate caffeine consumption does not increase cardiac arrhythmias.18
If regular caffeine consumption is stopped abruptly, symptoms such as headaches, irritability and fatigue may occur. These effects are usually temporary, disappearing after a day or so and can be avoided if caffeine cessation is gradual.
Caffeine and Health
The role of caffeine in the development of certain diseases and conditions has been the subject of extensive research in recent years.
Cancer
A number of studies investigating the impact of caffeine in the development of cancer have failed to establish a relationship.19-22 In fact, tea is one of the richest sources of flavonoids, a powerful group of antioxidants. The role of antioxidants in the prevention of free radical damage has led to suggestions that tea maybe anti-carcinogenic.23 Despite interesting preliminary research, further work is required to prove its beneficial effect in this area.
Heart Disease
A number of studies have investigated the relationship between caffeine and heart disease and results from these and epidemiological studies have led to the conclusion that the ingestion of moderate amounts of caffeine is not associated with any increased risk of heart disease.24-28 The Committee on Medical Aspects of Food Policy concluded that 'there is little evidence that caffeine itself has any relation with CHD risk' in the 1994 Nutritional Aspects of Cardiovascular Disease report.29
Parkinson's Disease
Observational studies have suggested that caffeine may play a role in protecting against Parkinson's disease,30-31 although further research is required to determine the exact mechanism.
Relief of headaches
In a study of 301 regular headache sufferers, researchers found that a combination of ibuprofen and caffeine was better than either drug alone in relieving pain.32 Although a caffeine 'pill' was used in this trial, the researchers believed that caffeinated beverages would work just as well. However, they did warn that chronic headache sufferers should avoid caffeine because it might exacerbate symptoms. More work is required in this field before firm conclusions about caffeine and pain relief can be drawn.
Pregnancy
Caffeine crosses the placenta and achieves blood and tissue concentrations in the foetus that are similar to maternal concentrations. For this reason recent advice published by the Food Standards Agency33 recommends that pregnant women should limit their intake of caffeine consumption to less than 300mg/ day (equivalent to 6 cups of tea/ day). At this level there is little evidence to suggest that the health of the unborn child or mother is affected.
In Summary.
Despite recent publicity about caffeine, the fact remains that the consumption of caffeine at intakes of 300mg/ day has no adverse effects in the vast majority of the adult population. For this reason an average intake of three to four cups of teas34 a day is well within the level considered safe.
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Tea and Iron Absorption
Introduction
Iron has several vital functions in the body, it's major role being as an Oxygen carrier in blood haemaglobin and muscle myoglobin. In addition, it is a component of many enzymes and is required for a number of metabolic processes. Deficiency in dietary iron is the most common nutritional deficiency in the world and can ultimately result in anaemia.
Sources of Dietary Iron
Dietary iron is available in two valence states, Fe 2+ (ferrous) and Fe 3+ (ferric). The majority of ferrous iron is found in haem iron and the majority of ferric iron is found in non-haem iron.
Haem iron is present in the haemaglobin and myoglobin of animals and as a result is found in meat, liver, offal and meat products. This form of iron is relatively available and typically 20-30% of haem iron is absorbed from the diet, although this can rise to 40% in situations of iron deficiency.1 The level of haem iron absorption is relatively unaffected by other dietary factors.
Non-haem iron is found in plant foods such as cereals, vegetables, pulses, dried fruit, etc and compared to haem iron it is relatively poorly absorbed, typically less than 10% and often under 5%. The absorption of non-haem iron is much more influenced by an individual's iron status and several factors in the diet that can either inhibit or enhance its absorption.
In the average UK diet, iron mainly comes from2:-
Cereal products (42%)
Meat and meat products (23%)
Vegetables (15%)
Enhancers of dietary non-haem iron absorption
Vitamin C found in fruit, fruit juice and vegetables, enhances iron absorption by reducing the ferric iron to the more readily absorbed ferrous form. In addition, it also protects any iron in the ferrous form from being oxidised back to the ferric form.
Animal products provide an unidentified substance that appears to promote the absorption of non-haem iron.
Organic acids such as citric acid and lactic acid (found in fermented products such as sauerkraut) have been found in some studies to enhance the absorption of non-haem iron. The nature of this effect has still yet to be established, although the lower pH in the duodenum, caused by these acids, helps to activate phytase (the enzyme responsible for the breakdown of phytate) in these products3.
Inhibitors of dietary non-haem iron absorption
Phytate found in the bran of wheat, oats, maize and other cereals strongly inhibit non-haem iron absorption by interacting with it, rendering it less soluble and thus less available for absorption.
Calcium appears to interfere with the absorption of iron,4,5 although the mechanism is unknown.
Phenolic compounds found in tea, coffee, red wine, some leafy vegetables, nuts and legumes are responsible for the inhibition of iron absorption. It appears to be the galloyl group in these compounds that is responsible for the inhibitory effects.3
Dietary Requirements and Deficiency
Individual requirements for dietary iron vary according to age, gender and diet. Low iron intakes are common in the UK population, especially females6. Other at risk groups include young infants, teenage girls, premenopausal and pregnant women and the elderly. Iron deficiency ultimately results in anaemia, however, functional consequences may occur even in the absence of anaemia7 , including adverse effects on work capacity, intellectual performance, behaviour and immunological responses.
Tea Drinking and Iron Absorption
Tea drinking mainly influences the absorption of non-haem iron as haem iron is relatively unaffected by tea.
The inhibitory effects of tea drinking on iron absorption was first identified in a study that used test meals fed under experimental conditions.8 A few studies have attempted to quantify the effect of tea on non-haem iron absorption .9-11 These studies concluded that tea does have an inhibiting effect on iron absorption, however it has been proposed that findings from experiments using human or animal models based on test meals fed under experimental conditions may not reflect the role of tea when consumed as part of a complex, real diet.12
Tea Drinking and Iron Status
It would be expected that if tea has a strong inhibitory affect on non-haem iron absorption it would be associated with a poor iron status. A number of population studies have investigated this hypothesis. Studies investigating tea drinking in children show a higher incidence of anaemia amongst tea drinkers compared to non-tea drinkers13-15
Results from studies in adults looking at the effects of tea drinking on iron status are conflicting. Mehta et al16 found a negative association between total cups of coffee and tea consumed and risk of anaemia. In contrast, Razagui, et al17 found that meal time drinking was strongly negatively associated with serum ferritin levels in a group of long stay mentally handicapped women.
Similar findings have been found in elderly subjects, where a low consumption of total iron, haem and non-haem iron and ascorbic acid, and higher intakes of calcium, dietary fibre and tea and coffee consumption was found in healthy subjects with low iron stores compared to those with good iron status.18
These short term studies indicate that there maybe a negative association between tea drinking and iron status in a number of different populations. However, these studies do not necessarily show cause and effect ie that negative iron status is as a result of tea drinking instead it shows that a group who had a low iron status also had a higher intake of tea. Moreover, they have not controlled adequately for other factors that are likely to affect iron status e.g. genetic factors, other dietary factors and status of an individual's iron stores. For this reason no firm conclusions can be drawn from these results. In an attempt to address these other factors, Dr Michael Nelson from King's College, London investigated the data from the National Diet and Nutrition Survey (NDNS) in a review on tea drinking and iron status19. Information from the NDNS is collected by social class thereby showing differences in dietary intakes according to a number of parameters and therefore likely to reveal any effect of diet on iron status. He concluded that there was no clear evidence from this survey that the higher levels of tea consumption found in the manual social class households is specifically associated with poorer iron status. Further studies are required in this area before any firm conclusions can be made. In addition, because the rate of iron absorption is dependent in part on iron status, some authors have concluded that people could adapt to low iron intakes or low iron bioavailability over time and maintain good iron status.20
Practical advice for tea drinking in relation to iron status
There is no evidence to suggest that tea drinking should be restricted in healthy individuals who are not at risk of iron deficiency and are consuming a well balanced, mixed diet.
People who have a poor iron status should avoid drinking tea with meals and up to at least one hour after the meal. Any adverse effects that tea may have on iron absorption are then likely to be minimised.
Certain groups are at higher risk of poor iron status, including infants and toddlers, teenage girls, premenopausal women and men aged 75 years and over. Based on the published evidence in the UK, the higher rates of poor iron status amongst these groups cannot be directly linked to tea drinking. However, it would be prudent to recommend that tea is not drunk with meals or up to one hour after the meal.
Moderate tea drinking (3-4 cups) spread throughout other times of the day is unlikely to have any adverse effect on iron status. The inhibitory effect of tea on iron absorption maybe partially overcome by the simultaneous consumption of animal tissues and Vitamin C.21
In Summary.
Tea consumption will not result in iron deficiency for healthy individuals who are consuming a varied and balanced diet.
The absorption of iron from food is generally low and is influenced by a number of factors including the quantity of iron consumed, the chemical form (haem versus non-haem), interaction with other dietary factors and the individual's physiological condition (status of iron stores, period of growth, menstruation or pregnancy).
Haem iron present in good amounts in meat, offal and meat products is readily absorbed and is unaffected by tea drinking. Non-haem iron found in cereals, vegetables, dried fruit, legumes and nuts is less well absorbed and its absorption is influenced by a wide variety of dietary factors which include enhancers e.g Vitamin C (present in fruit and fruit juice) and animal tissue (meat), and inhibitors e.g. phytate (bran) and tea (polyphenols).
Therefore for those who have a poor iron status or are at high risk of iron deficiency it would be prudent to avoid drinking tea with meals.
Otherwise moderate tea drinking (3-4 cups) spread throughout other times of the day is unlikely to have any adverse effect on iron status, and in fact at this level can actually bring about other health benefits thereby helping to promote overall health and well being.
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Origins of Tea
Origins of Tea
The story of tea began in ancient China over 5,000 years ago. According to legend, Shen Nung, an early emperor was a skilled ruler, creative scientist and patron of the arts. His far-sighted edicts required, among other things, that all drinking water be boiled as a hygienic precaution.
One summer day while visiting a distant region of his realm, he and the court stopped to rest. In accordance with his ruling, the servants began to boil water for the court to drink. Dried leaves from the near by bush fell into the boiling water, and a brown liquid was infused into the water. As a scientist, the Emperor was interested in the new liquid, drank some, and found it very refreshing. And so, according to legend, tea was created. (This myth maintains such a practical narrative, that many mythologists believe it may relate closely to the actual events, now lost in ancient history.)
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Chinese / Japanese Influence
The Chinese Influence
Tea consumption spread throughout the Chinese culture reaching into every aspect of the society. In 800 A.D. Lu Yu wrote the first definitive book on tea, the Ch'a Ching. This amazing man was orphaned as a child and raised by scholarly Buddhist monks in one of China's finest monasteries. However, as a young man, he rebelled against the discipline of priestly training which had made him a skilled observer. His fame as a performer increased with each year, but he felt his life lacked meaning.
Finally, in mid-life, he retired for five years into seclusion. Drawing from his vast memory of observed events and places, he codified the various methods of tea cultivation and preparation in ancient China. The vast definitive nature of his work, projected him into near sainthood within his own lifetime. Patronized by the Emperor himself, his work clearly showed the Zen Buddhist philosophy to which he was exposed as a child. It was this form of tea service that Zen Buddhist missionaries would later introduce to imperial Japan.
The Japanese Influence
The first tea seeds were brought to Japan by the returning Buddhist priest Yeisei, who had seen the value of tea in China in enhancing religious mediation. As a result, he is known as the "Father of Tea" in Japan. Because of this early association, tea in Japan has always been associated with Zen Buddhism. Tea received almost instant imperial sponsorship and spread rapidly from the royal court and monasteries to the other sections of Japanese society.
Tea was elevated to an art form resulting in the creation of the Japanese Tea Ceremony ("Cha-no-yu" or "the hot water for tea"). The best description of this complex art form was probably written by the Irish-Greek journalist-historian Lafcadio Hearn, one of the few foreigners ever to be granted Japanese citizenship during this era. He wrote from personal observation, "The Tea ceremony requires years of training and practice to graduate in art...yet the whole of this art, as to its detail, signifies no more than the making and serving of a cup of tea. The supremely important matter is that the act be performed in the most perfect, most polite, most graceful, most charming manner possible".
Such a purity of form, of expression prompted the creation of supportive arts and services. A special form of architecture (chaseki) developed for "tea houses", based on the duplication of the simplicity of a forest cottage. The cultural/artistic hostesses of Japan, the Geishi, began to specialize in the presentation of the tea ceremony. As more and more people became involved in the excitement surrounding tea, the purity of
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Europe Learns of Tea
While tea was at this high level of development in both Japan and China, information concerning this then unknown beverage began to filter back to Europe. Earlier caravan leaders had mentioned it, but were unclear as to its service format or appearance. (One reference suggests the leaves be boiled, salted, buttered, and eaten!) The first European to personally encounter tea and write about it was the Portuguese Jesuit Father Jasper de Cruz in 1560. Portugal, with her technologically advanced navy, had been successful in gaining the first right of trade with China. It was as a missionary on that first commercial mission that Father de Cruz had tasted tea four years before.
The Portuguese developed a trade route by which they shipped their tea to Lisbon, and then Dutch ships transported it to France, Holland, and the Baltic countries. (At that time Holland was politically affiliated with Portugal. When this alliance was altered in 1602, Holland, with her excellent navy, entered into full Pacific trade in her own right.)
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Tea Comes to Europe
When tea finally arrived in Europe, Elizabeth I had more years to live, and Rembrandt was only six years old. Because of the success of the Dutch navy in the Pacific, tea became very fashionable in the Dutch capital, the Hague. This was due in part to the high cost of the tea (over $100 per pound) which immediately made it the domain of the wealthy. Slowly, as the amount of tea imported increased, the price fell as the volume of sale expanded. Initially available to the public in apothecaries along with such rare and new spices as ginger and sugar, by 1675 it was available in common food shops throughout Holland.
As the consumption of tea increased dramatically in Dutch society, doctors and university authorities argued back and forth as to the negative and/or positive benefits of tea. Known as "tea heretics", the public largely ignored the scholarly debate and continued to enjoy their new beverage though the controversy lasted from 1635 to roughly 1657. Throughout this period France and Holland led Europe in the use of tea.
As the craze for things oriental swept Europe, tea became part of the way of life. The social critic Marie de Rabutin-Chantal, the Marquise de Seven makes the first mention in 1680 of adding milk to tea. During the same period, Dutch inns provided the first restaurant service of tea. Tavern owners would furnish guests with a portable tea set complete with a heating unit. The independent Dutchman would then prepare tea for himself and his friends outside in the tavern's garden. Tea remained popular in France for only about fifty years, being replaced by a stronger preference for wine, chocolate, and exotic coffees.
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