Green teas have about a quarter the caffeine content, by liquid volume, of coffee. Green tea has been credited with providing a wide variety of health benefits, many of which have not been validated by scientific evidence. Green tea also seems to protect the liver from the damaging effects of toxic substances such as alcohol. Green tea and aspirin should not be mixed because they both prevent platelets from clotting. Green tea and the risk of breast cancer: pooled analysis of two prospective studies in Japan.
Green tea drinkers appear to have lower risk for a wide range of diseases, from simple bacterial or viral infections to chronic degenerative conditions including cardiovascular disease, cancer, stroke, periodontal disease, and osteoporosis. Green tea consumption has been shown to enhance survival in women with ovarian cancer. Green tea extract has been shown, via a mechanism that affects cell movement, to target cancer cells while leaving healthy cells alone. Green tea's catechins appear to stimulate the use of fatty acids by liver and muscle cells.
Green tea's effect on muscle cells' ability to take in and burn fatty acids, speeding up fat breakdown, is also thought to be the reason why it helps weight loss. Green tea drinking is associated with increased bone mineral density in elderly women. Green tea contains small amounts of vitamin K, which can make anticoagulant drugs, such as warfarin, less effective. Green tea is also promotedas an herb that can prevent certain bacterial infections. Green tea is common in Egypt, and it's likely that many people there drink it while taking antibiotics. Japanese researchers claim that drinking five cups of green tea a day can burn 70 to 80 extra calories.
The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both. Several case control studies suggest an inverse relation between green tea consumption and gastric cancer. There is also research indicating that drinking green tea lowers total cholesterol levels, as well as improving the ratio of good (HDL) cholesterol to bad (LDL) cholesterol. Researchers found that men who were given a combination of caffeine and green tea extract burned more calories than those given only caffeine or a placebo. Antioxidants such as polyphenols in green tea can neutralize free radicals and may reduce or even help prevent some of the damage they cause.
In one study of 472 women with various stages of breast cancer, researchers found that women who consumed the most green tea experienced the least spread of cancer (particularly premenopausal women in the early stages of breast cancer). In one large-scale study researchers compared green tea drinkers with non-drinkers and found that those who drank the most tea were significantly less likely to develop pancreatic cancer.