Depression risk in women may decrease with increased consumption of caffeinated coffee, according to a new study. Caffeine is the most frequently used central nervous system stimulant in the world, and approximately 80 per cent of consumption is in the form of coffee, according to background information in the article. Michel Lucas, Ph.D., R.D., from the Harvard School of Public Health, Boston, and colleagues studied 50,739 U.S. women who participated in the Nurses' Health Study. Researchers measured caffeine consumption through questionnaires completed from May 1980 through April 2004. During the 10-year follow-up period from 1996 to 2006, researchers identified 2,607 incident (new-onset) cases of depression. When compared with women who consumed one cup of caffeinated coffee or less per week, those who consumed two to three cups per day had a 15 per cent decrease in relative risk for depression, and those consuming four cups or more per day had a 20 per cent decrease in relative risk. Compared with women in the lowest (less than 100 milligrams [mg] per day) categories of caffeine consumption, those in the highest category (550 mg per day or more) had a 20 per cent decrease in relative risk of depression. No association was found between intake of decaffeinated coffee and depression risk. "In this large prospective cohort of older women free of clinical depression or severe depressive symptoms at baseline, risk of depression decreased in a dose-dependent manner with increasing consumption of caffeinated coffee," write the authors. They note that this observational study "cannot prove that caffeine or caffeinated coffee reduces the risk of depression but only suggests the possibility of such a protective effect." The study was recently published in archives of Internal Medicine , one of the JAMA/Archives journals .