Health benefits of tea
From Wikipedia, the free encyclopedia
- In this article, the word "tea" is limited to its traditional meaning, an infusion made from the plant Camellia sinensis.
Claims have been made regarding the health benefits of tea consumption since the beginning of its history 5,000 years ago.
The possible beneficial health effects of tea consumption have been suggested and supported by some studies, but others have not found beneficial effects. One should consult a doctor before using high concentrations of tea for disease prevention. Ingestion of large amounts of tea may cause nutritional and other problems because of the strong binding activities of tea polyphenols and the caffeine content, although no solid data exist concerning harmful effects of tea consumption. [1]
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[edit] Benefits from tea
[edit] Green tea
Some scientific studies [2] indicate that green tea may be helpful for the following health conditions:
- Atherosclerosis
- High cholesterol
- Cancer; including Bladder cancer, Breast cancer, Colorectal cancer, Esophageal cancer, Lung cancer, Pancreatic cancer, Prostate cancer, Skin cancer, Stomach cancer
- Inflammatory bowel disease
- Diabetes
- Liver disease
- Weight loss
- Cognitive impairment
[edit] Anti-cancer properties
Studies claim that the polyphenol content of green tea has antioxidant properties that can help prevent cancer, however research is ongoing. There is also a suggestion that it can increase endurance in exercise by improving fat metabolism. [3]
An article in New Scientist magazine (20 March 2004) mentions that numerous studies suggest that green tea protects against a range of cancers, including lung, prostate and breast cancer. The reason is the antioxidant epigallocatechin gallate (EGCG), according to Hirofumi Tachibana's team at Kyushu University in Japan. Their research showed that growth of human lung cancer cells that have a cell receptor called 67 LR is slowed significantly after drinking just two or three cups of green tea, which contains EGCG. The research also showed that 67 LR is involved in the propagation of prion diseases such as mad cow disease in humans. So knowledge of EGCG's effect on 67 LR might have implications in the treatment of these diseases too. (Full report in Nature Structural and Molecular Biology, DOI:10.1038/nsmb743).
According to the U.S. National Cancer Institute, in laboratory studies using animals, catechins inactivated oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells. White tea is said to be even more effective. However, human studies have proven more contradictory, perhaps due to such factors as variances in diet, environments, and populations. White tea has more catechins than any other known product, with green tea a close second. However, white tea is generally more expensive than green tea.
[edit] Increases metabolic rate
Clinical trials conducted by the University of Geneva in Switzerland indicate that green tea raises metabolic rates and speeds up fat oxidation. In addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are burned), and hence increases energy expenditure.
[edit] Possible anti-diabetes effect
There is also epidemiological evidence that drinking green tea (but not black tea or oolong tea) may help prevent diabetes,[1] although it is worth noting that this is evidence of an association, but that prospective studies are needed to confirm the effect.
[edit] Boosts immune system and mental alertness
On 21 April 2003 the Brigham and Women's Hospital released details of a research project which indicated that the amino acid L-theanine (found most readily in green, black, oolong and pekoe teas) may help the body's immune system response when fighting infection, by boosting the disease-fighting capacity of gamma delta T cells. The study included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600ml of coffee or black tea daily. Blood sample analysis found that the production of anti-bacterial proteins was up to five times higher in the tea-drinkers, an indicator of a stronger immune response.[4]
L-theanine has also been found to increase alpha wave production in the brain, which is associated with a state of "alert relaxation".
[edit] Lowers chances of cognitive impairment
A 2006 study showed that elderly Japanese people who consumed more than 2 cups of green tea a day had a 50 per cent lower chance of having cognitive impairment, in comparison to those who drank less than 2 cups a day, or who consumed other tested beverages. Ref: [[5]]. Green tea has 67.5 mg catechins per 100 ml, and this might explain the results. The study was published in "The American Journal of Clinical Nutrition" (Vol. 83, pp.355-361).
[edit] Lowers stress hormone levels
According to a study by UCL researchers published in the journal Psychopharmacology, drinking black tea has an effect on stress hormone levels in the body and thus helps in recovering more quickly from life's stresses. The study showed that, 50 minutes after a high stress event, subjects who drank 4 cups of black tea per day for a 4 week period experienced an average cortisol drop of 47%, compared to 27% for the placebo group. Blood platelet activation, which is linked to blood clotting and the risk of heart attacks was also lower in the tea drinker's group.[6]
[edit] United States FDA
In a July, 2005 review of claims made about the health benefits of green tea, the U.S. Food and Drug Administration concluded that it was highly unlikely that green tea reduces the risk of breast and prostate cancer. Further, the FDA believes that current evidence does not support qualified health claims for green tea consumption and a reduced risk of cancer.[7]
The FDA has not been able to square its findings with the findings of extensive tea experiments in Asia. However, the Asian results only demonstrate a association between drinking tea and being healthy. They do not show that drinking tea causes better health. It may just be that healthy people like tea.
[edit] See also
[edit] External links
- FDA says studies supporting assertions that Green Tea lowers cancer risk are weak
- Green tea information from the University of Maryland Medical Center
- Some evidence for the benefits of green tea for endurance in exercise
- Tea and Cancer Prevention - National Cancer Institute press release
- Antioxident in Green Tea May Fight Alzheimer's, (EGCG)
- "Drinking Tea May Boost Immune System" (Press release of Brigham and Women's Hospital, 21 April 2003).
- "Tea 'healthier' drink than water" - BBC article, 24 August 2006
[edit] References
- ^ Iso H et al. (2006). "The Relationship between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes among Japanese Adults" 144 (8): 554–62.
