According to a new study conducted by researchers at the Harvard School of Public Health and published in the July 2 online edition of The World Journal of Biological Psychiatry, drinking several cups of coffee each day can reduce the risk of suicide by about 50 percent in both men and women.

“Unlike previous investigations, we were able to assess association of consumption of caffeinated and non-caffeinated beverages, and we identify caffeine as the most likely candidate of any putative protective effect of coffee,” said Michel Lucas, lead researcher and research fellow in the Department of Nutrition at HSPH.

Researchers reviewed data collected during three large U.S. based studies and found the suicide risk in adults who drank two to four cups of caffeinated coffee each day was half of that of individuals who drank decaffeinated coffee or none at all.

Caffeine stimulates the central nervous system, but it could also act as a mild antidepressant by boosting production of specific neurotransmitters in the brain, such as serotonin, dopamine and noradrenaline. This could be the explanation for the lower risk of depression among coffee drinkers that was discovered in past studies, according to the researchers.

During this recent study, researchers viewed the data of 43,599 men who participated in the Health Professionals Follow Up Study (1988-2008), 73,820 women who participated in the Nurses’ Health Study ( 1992-2008) and 91,005 women who participated in the Nurses’ Health Study II(1993-2007). Caffeine, coffee and decaffeinated coffee intake was assessed every 4 years by questionnaire. Caffeine consumption was calculated from coffee, tea, soft drink and chocolate intake. Coffee accounted for the majority of caffeine intake in all three studies. Among all participants in the studies, 277 deaths occurred as a result of suicide.

Despite these recent findings, the researchers do not recommend increased caffeine intake by depressed individuals because an increase could result in unwanted side effects. Researchers wrote, “Overall, our results suggest that there is little further benefit for consumption above two to three cups/day or 400 mg of caffeine/day.”

No major difference was observed between individuals who drank two to three cups per day and those who drank four or more per day. This was likely due to the small number of suicide deaths in those categories. A Finnish study showed a higher risk of suicide among individuals who drank eight or more cups of coffee per day. Very few participants in the data used for this most recent study reported such a large consumption, so the impact of six or more cups was not addressed.