The potential health effects of tea drinking have been studied ever since its first recorded usage in China approximately 5000 years ago. The possible health benefits of tea have been the subject of more recent study, with some claims supported by scientific evidence and other claims found to be unsubstantiated.

Most of the claims of health benefits (and consequently, most scientific study) are based around green tea. It has been claimed that green tea can be helpful in numerous conditions including cancer, Inflammatory Bowel Disease, diabetes, cholesterol, liver disease and weight loss.

Cancer Protection

Tea is considered by many to provide anti-cancer properties, mainly due to the high levels of antioxidants associated with tea. A number of studies have suggested that green tea can provide some protection against cancers such as lung, breast and prostate cancer. Research has shown that due to a specific antioxidant (epigallocatechin gallate – EGCG) growth of lung cancer can slow significantly after only two or three cups of tea. Topical application of EGCG has also been shown to have protective qualities over UVA and UVB carcinogenesis. Another study has shown that green tea, used in combination with other substances, can have the effect of suppressing the growth of breast cancer.

Inflammatory Bowel Disease

There is some evidence that the polyphenols in green tea can reduce intestinal inflammation in IBD. In some relatively recent studies of mice (2007), one group of mice were fed water alone and another group fed water with polyphenols from green tea. At the end of the six week study, the green tea group of mice has less severe colitis and had shown greater weight gain. In another recent study, rats were subjected to experimental colitis and then treated with green tea extract. In this study, treatment with green tea significantly reduced the diarrhoea and loss of body weight in the rats.

Weight Loss and Cholesterol

Scientific trials have indicated that tea can raise metabolic rate and speed up the oxidation of fat in the body. It is speculated that it is the caffeine in tea which helps improve fat oxidation, however, it has been shown in studies that even those who drink decaffeinated tea varieties also lose more weight than those who do not drink tea at all. Caffeine consumption itself is thought to have a number of health benefits including a reduction in the probability of Parkinson’s disease. Green tea and its extracts have also been shown to reduce levels of "bad" cholesterol.

Cardiovascular Health

Other research indicates that tea may have positive effects on cardiovascular health. University studies performed in 2009 reveal that drinking black tea can have the effect of improving blood vessel reactivity and reduce blood pressure and hardening of the arteries. Along with the potential reduction in cholesterol, it is possible that drinking tea can result in an improved cardiovascular health profile.