 Tea is a natural plant, only differing in taste and character because of the area in which it is grown, the type of soil (tea plants like acidic soil) and the altitude and climatic conditions of the area.
Select a topic below to discover more about the constituents of tea:
Scientific researchers are investigating how tea drinking can protect us from certain diseases. Select a topic below to discover more about the effects of tea:
Black tea contains small amounts of a number of vitamins considered essential for maintaining health:
- Carotene, a precursor to vitamin A, has antioxidant and protective properties.
- Thiamin (vitamin B1) and riboflavin (vitamin B2) are both essential for releasing energy from food.
- Nicotinic acid and pantothenic acid are necessary for the release of energy from fat and carbohydrate.
- Ascorbic acid (vitamin C) is essential for a healthy immune system.
- Vitamin B6 is involved in the metabolism of proteins.
Folic Acid plays a role in cell division. The average daily consumption of tea in the UK (24fl.oz), drunk with semi skimmed milk, provides:
- 9% of the daily requirement of Vitamin B1
- 25% of the daily requirement of Vitamin B2
- 6% of the daily requirement of Vitamin B6
- 10% of the daily requirement of Folic Acid
Tea is a rich source of two minerals essential for health:
Manganese
Manganese is essential for bone growth and the body's development and 2-5mg a day is required for good health. Tea is one of the richest sources of manganese in our diet, with 5-6 cups of tea providing 45% of our daily requirement.
Potassium
Potassium is vital for maintaining a normal heart beat. It enables nerves and muscles to function and regulates fluid levels within the cells. Deficiency leads to erratic heartbeat and fatigue.
A normal, balanced diet should provide sufficient potassium for health. However, eating disorders such as anorexia and bulimia and over exercise may lead to deficiency.
Diuretics also lead to loss of potassium, so women who use diuretics to counteract water retention around the time of their period or those prescribed them for high blood pressure may also be at risk of deficiency.
Tea is a rich source of potassium. 5-6 cups provides nearly 3/4 of the recommended daily intake for an adult.
Although the oxygen we breath is vital to life, it is also incorporated into very reactive substances called free radicals which are harmful to our bodies. Free radicals cause damage to the components of our cells and have been implicated in the slow chain reaction of damage leading to heart disease and cancer. Antioxidants in our diet help to prevent and repair the damage caused by free radical attack.
The best known antioxidants are vitamins C, E and beta carotene, found in fruit, vegetables, cereals and vegetable oils. These are known as the 'ACE' vitamins.
Tea (both green and black) is also a rich source of antioxidants called flavanoids. There is a growing body of evidence which confirms that those flavanoids play an important role in protecting us from heart disease and cancer.
Fluoride is the most successful agent against tooth decay ever discovered.
Tea is one of the few natural sources of fluoride (depending on the type and strength of tea) and has been shown to have a positive effect on preventing tooth decay and gum disease.
Scientists believe that drinking tea improves oral health by helping prevent dental caries. A British study published in 1991 suggested that heavy tea drinking could even provide some children with enough fluoride to prevent tooth decay. It has also been suggested that plaque, the scale caused by mouth bacteria that leads to gum disease, is decreased by drinking tea. These effects are probably due to tea's antioxidant components working in synergy with its fluoride content.
Tea and Heart Disease Prevention
The natural antioxidant properties of tea may help combat the risk of developing Coronary Heart Disease. Research has suggested that drinking around 4-5 cups of tea a day may have a beneficial effect on two long established heart disease risk factors: high blood cholesterol and high blood pressure. Studies have shown that average blood cholesterol and blood pressure drop, as tea consumption increases and experts believe the flavanoids in tea are responsible for the effect. Other studies have shown that tea flavanoids may also decrease blood clotting which is another common cause of cardiovascular disease.
How Tea May Be a Heart-Saver
The natural antioxidant properties of tea may help reduce the risk of developing heart disease. Studies have provided evidence that it is the polyphenols in tea that have a beneficial effect on two long established heart disease risk factors:
- high blood cholesterol
- high blood pressure
Cholesterol levels Studies have indicated that average blood cholesterol levels drop as the amount of tea consumed increases.1 Published evidence has shown trends towards lower systolic blood pressure levels (systolic) as tea drinking levels go up.2 Heart Disease: Research Studies
The latest human study3 shows that tea significantly increases antioxidant activity. Amongst twenty-one volunteers who were tested for six days, and given the equivalent of three cups of tea a day, researchers found an increase of antioxidants in their blood plasma levels.
Another study4, published in the American Journal of Epidemiology and reported in The Lancet, indicated that the risk of heart attack in people who drank one, or more cups of tea a day was about half that of those who drank no tea. The researchers suggested that the benefits of drinking tea may be attributed to the high concentration of flavonoids which reduce blood clotting and the deposition of cholesterol in the blood vessels.
Several other research studies have also demonstrated teaÕs positive effect on heart disease. A Scandinavian study5 of men aged between 50-69, showed that drinking 4-5 cups of tea a day reduced the risk of stroke by 69% and other studies6 have indicated that drinking 4-5 cups of tea a day may also have a beneficial effect on high blood cholesterol and high blood pressure.
"These exciting studies offer further information about the role that dietary flavonoids may play in reducing the risk of circulatory diseases."
Dr Simon Maxwell, Clinical Pharmacologist, Edinburgh University
Tea and cancer prevention
Tea consumption may have beneficial effects in reducing cancer risk in certain populations. As tea is one of the most popular drinks in the world, any possible relationship between its consumption and a reduced incidence of cancer in humans is of great significance.
A wide spectrum of studies, both in the laboratory and in human populations, looking at the relationship between tea consumption and cancer generally indicate a protective effect of tea.
Tea and Cancer: Research Studies
Results of the most recent preliminary research7 published in Nutrition and Cancer indicated that tea may protect against the development of pancreatic and prostate cancer. Researchers from the National Centre for Toxicological Research in the United States, extracted theaflavins and polyphenols and demonstrated that they significantly inhibited the growth of human pancreatic and prostate tumour cells. Their research also indicated that tea could have a role to play in changing the genes involved in the process of causing cancer.
"This study provides further evidence concerning the anti-properties of tea consumption. These new results are very preliminary and are based on test-tube experiments, but if confirmed in further research and supported by human studies, they could provide new insights into the prevention of pancreatic and prostate cancer"
Professor David Forman, Centre for Cancer Research, University of Leeds
Another study8, published in the International Journal of Cancer indicated that men who drink between 2 and 3 cups per day may reduce their risk of developing prostate cancer by up to 30% compared to non-tea drinkers. Researchers from the University of Toronto looked at the complete history of beverage intake amongst 617 men who were suffering from prostate cancer and compared them with 637 healthy men. The results of the study suggested that the benefits of drinking tea may be attributed to the high concentration of certain antioxidants called phytochemicals which help the body fight harmful free radicals.
References
1. Green MS, Harari G. Association of serum lipoproteins and health related habits with tea consumption in free-living subjects examined in the Israeli CORDIS Study. Preventative Medicine 1992; 21 : 532-545
2. Stensvold I, Tverdal A, Solvoll K, Per Foss O. Tea consumption. Relationship to cholesterol, blood pressure, and coronary and total mortality. Preventative Medicine 1992; 21 : 546-553
3. Leenan, R, Roodenburg, AJC, Tijburg, LBM, Wiseman, SA. A single dose of tea with or without milk increase plasma antioxidant activity in humans. European Journal of Clinical Nutrition (2000) 54, 87-92
4. Sesso HD, et al. Coffee and tea intake and the risk of myocardial infarction. Am J Epidemiol. 1999 Jan 15; 149 (2): 162-7
5. Keli SO and others. Dietary flavonoids, antioxidant vitamins, and incidence of stroke. The Zutphen Study. Archives of Internal Medicine 1996; 156:637-42
6. Effect of black tea drinking on blood lipds, blood pressure and aspects. Bingham-S-A, Vorster-H, Jerling-J-C, Magee-E, Mulligan-A, Runswick-S-A, Br-J-Nutr 1997 Jul, VOL: 78 (1), P:41-55, issn: 0007-1145
7. Lynn-Cook BD, Rogers T, Yan Y, Blann EB, Kadlubar FF & Hammons GJ. (1999). Chemopreventative effects of tea extracts and various components on human pancreatic and prostate tumor cells in vitro. Nutrition & Cancer, 35(1): 80-86.
8. Meera Jain, Gregory Hislop, Geoffrey Howe, Alcohol and other beverage use and prostate cancer risk among Canadian Men International Journal of Cancer: 78, 707-711 (1998)
Alkaloids Naturally occurring, nitrogen-containing compounds that are alkaline in solution. They usually have a bitter taste and are characterised by powerful physiological activity. Examples are nicotine and caffeine.
Antioxidant A compound which retards oxidation.
Caffeine An alkaloid found in tea and coffee which acts as a nerve stimulant and diuretic.
Catechins A group of related polyphenolic compounds which occur in plants and are darkened by the action of certain plant enzymes and oxygen an example of browning of cut fruit and vegetables. Catechins can function as antioxidants.
Cardiovascular concerning the heart and blood vessels.
Carcinogen Any substance or agent that can produce a cancer.
Diuretic An agent that promotes increased excretion of urine.
Electrophilic ultimate carcinogens Substances which directly cause cancer by reacting with genetic material (DNA) and related cell components. (Many carcinogens, designated pro-carcinogens (q.v.), require conversion to the ultimate carcinogen by reactions taking place in the cells of the organism)
Epigallocatechin Gallate (EGCG, ECG, EGC, EC) A family of substances related to the simple catechins which occur in green tea and which undergo browning reactions during processing to black tea.
Free radical A highly reactive substance which, in some circumstances can lead to undesirable chemical changes in the body through oxidisation, e.g. hardening of the blood vessels and development of cancer.
Flavanoids, flavanols, flavonol glycosides, flavandiols Groups of related, naturally occurring chemicals in plants. A number of substances in these classes have anti-oxidant properties and many protect against deleterious changes brought about by free-radicals in the body.
Gallic acid A plant polyphenolic which possess antioxidant properties.
Lipid A member of the family of fats which occur in living tissues either structurally or for nutritional purposes.
Nicotinic acid A water soluble vitamin B complex.
Oxygen symbol O. A colourless, odourless gas constituting one-fifth of the atmosphere.
Oxidation Changes which are brought about by oxygen.
Polyphenols Compounds which contain several `phenol' groups and have antioxidant properties.
Polyphenolic components Chemicals found in plants which have several groups containing an oxygen and a hydrogen atom (called a phenol group).
Procarcinogen A substance capable of causing cancer but only when metabolised to a more reactive compound.
Riboflavin Vitamin B2
Theaflavins Yellow coloured polyphenols occurring in black tea.
Thearubigins Red/brown pigments produced in black tea.
Source: www.teahealth.co.uk |
