Japanese researchers have found that elderly men and women who drink 4 or more cups of green tea each day significantly reduce their likelihood of suffering from depression. When compared with those who consumed 1 or less cups of green tea daily, those consuming 4 or more cups were 44 percent less likely to suffer from depression. These effects also did not fade after they factored in social and economic status, gender, diet, history of medical problems, use of antidepressant medications, smoking, and physical activity. According to researchers, it is thought that the amino acid present in green tea, theanine, is thought to have a tranquilizing effect on the brain which may explain the beneficial effect of lowering depression related symptoms. A number of other studies have also shown green tea effective in reducing psychological stress.
Source: American Journal of Clinical Nutrition. December 2009.