Researchers at Harvard University have discovered that drinking several cups of coffee per day appears to reduce the risk of suicide among adults by approximately 50 percent.

The study, published earlier this month in the The World Journal of Biological Psychiatry, examined 43,599 men enrolled in the Health Professionals Follow-up Study (1988–2008), 73,820 women in the Nurses’ Health Study (1992–2008), and 91,005 women in the Nurses’ Health Study II (1993–2007). Researchers determined that the risk of suicide for adults who drank two to four cups of caffeinated coffee per day was about half that of those who drank decaffeinated coffee or very little or no coffee.

“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,” lead researcher Michel Lucas said in an announcement of the study. The research team linked the suicide rate reduction to previous research that found reduced rates of depression among coffee drinkers:

Caffeine not only stimulates the central nervous system but may act as a mild antidepressant by boosting production of certain neurotransmitters in the brain, including serotonin, dopamine, and noradrenaline. This could explain the lower risk of depression among coffee drinkers that had been found in past epidemiological studies, the researchers reported.

For the record, an increase in coffee consumption does not necessarily correlate to the reduced incidence of suicide. The researchers suggested about two to three cups per day, or about 400 mg of caffeine:

The researchers didn’t observe any major difference in risk between those who drank two to three cups of coffee per day and four or more cups/day, most likely due to the small number of suicide cases in these categories. However, in a previous HSPH coffee-depression study published in JAMA Internal Medicine, the investigators observed a maximal effect among those who drank four or more cups per day. One large Finnish study showed a higher risk of suicide among people drinking eight or nine cups per day. Few participants in the two HSPH studies drank such large amounts of coffee so the impact of six or more cups/day of coffee was not addressed in these two studies.