Tea has long been thought to improve health and slow the effects of aging. Traditional Chinese medicine recommends green tea for headaches, body aches and pains, digestion, depression, detoxification and to prolong life. A scientific review of the benefits of tea have found associations between increased tea drinking and reduction in the risk for heart disease, Parkinson’s disease and some cancers.
Tea contains many substances which might have an effect on health. Tea is particularly rich in flavonoids; pigments which produce the colours in plants. The main type of flavonoid found in green tea are catechins, a type of antioxidant. Antioxidants reduce the oxidation of other molecules. Oxidation can cause chain reactions that may damage cells. This type of damage is common in heart diseases, cancers and age-related diseases such as Parkinson’s and Alzheimer’s. Increased tea drinking may increase the amount of catechins in the body and therefore reduce the risk of damage to cells. It was originally thought that adding milk to tea might reduce the antioxidant effects. However, more recent studies have shown that adding milk or lemon does not affect flavonoid absorption or antioxidant capabilities of tea.
Both green and black tea are also a source of fluoride which help to prevent tooth loss and oral cancer. Green tea is also associated with increased bone mineral density. Poor bone density is a major risk factor for bone breaks and fractures. Green tea might promote activity of certain bone cells which help to increase bone density. This is especially important for women, and especially as they age. One group of researchers found that female tea drinkers aged 65 – 76 had significantly higher bone density in their hips and lower spine than non-tea drinkers of the same age. The researchers suggested that this might help protect against them osteoporosis (a condition in which bones become weaker and more likely to break).
Drinking green tea might also play a role in weight management. It is thought that drinking green tea may stimulate the metabolism to promote fat burn. Green tea also increases the activity of insulin which regulates blood sugar balance within the body. Long periods of high blood sugar are thought to lead to a condition called ‘insulin resistance’ which can lead to the development of Type 2 diabetes. Therefore, the ability of green tea to increase insulin activity may help regulate blood sugar levels. Interestingly, one study found that adding milk to tea decreased this effect by up to 90%.
Tea drinking might also help protect against cancer. Green tea has been found to reduce the development of cancer cells in the skin, lungs, mouth, throat, stomach, liver, kidney and other organs. One group of researchers found breast cancer to be significantly less common in Asian women whose diets contain high levels of soy products and green tea. They therefore suggested that dietary soy intake alongside with green tea drinking might be affective at slowing the development of breast cancer.
Despite the research which finds tea drinking to have a positive effect on health, some studies have found no effects and others have found negative effects. For example, only 2 out of 9 studies of the effects of green tea drinking on stroke risk found increased tea consumption to be associated with reduced stroke risk; the other 7 studies found no association. One study also found increased black tea drinking to increase the risk of heart disease. This finding is in conflict to previous research and there is still much debate about the reason for these results. One proposal is that many of the participants in the study who reported high levels of tea consumption may have been heavy smokers; smoking is known to be associated with heart disease and this might explain the association. These findings show that the conclusions drawn about the effects of tea drinking on health should be made carefully and outline the need for more research into this field to be conducted.
 Cabrera, Artacho & Gimenez (2006) Beneficial Effects of Green Tea – A Review
 Higdon & Frei (2003) Tea catechins and polyphenols: Health effects, metabolism and antioxidant functions