Reviewing data from three large-scale U.S. studies, the team from the Harvard School of Public Health compared the risk of suicide for adults who consumed two to four caffeinated cups per day with that of non-coffee drinkers, those who drank much less coffee per day and people who chose decaf.
The results, published earlier this month in The World Journal of Biological Psychiatry, were striking. Comparatively, the suicide risk for those who drank two to four cups per day was about 50 percent less than the risk for subjects in the other groups. (The total sample included more than 200,000 participants, who were studied for time spans of at least 16 years.)
"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, a research fellow in the university's department of nutrition, said in a statement.
The team's findings are, perhaps, not surprising since caffeinated coffee has been linked to a lower risk of depression among women in the past. In a 2011 study, also conducted by Harvard researchers, women who drank coffee were shown to have a 15 percent reduced risk of depression as compared to non-coffee drinkers.
Lucas also stressed that it's the caffeine in coffee that's primarily responsible for these effects. He linked the lowered risks of depression and suicide to the impact caffeine has on the brain or, more specifically, on neurotransmitters that have been shown to have an effect on emotions.
And while other drinks like soda and tea also offer caffeine, they don't contain nearly the same levels as coffee.
"Caffeine from coffee is about 80 percent caffeine intake," Lucas estimated. "In one cup of coffee, you could have about 140 mg of caffeine."
"In tea, for example, you have about 47 mg," he told the reporters, adding that someone would need about three more cups of tea to achieve the same effect as one cup of coffee.
However, as the researchers indicated in the study, moderation is still key. (Though caffeine intoxication was already a disorder in the Diagnostic and Statistical Manual of Mental Disorders, the latest version, DSM-5, added caffeine withdrawal as a related diagnosis.)
"Overall, our results suggest that there is little further benefit for consumption above two to three cups/day or 400 mg of caffeine/day," the authors wrote.
The Harvard study joins a growing body of scientific evidence, which has provided confirmation of the health benefits of coffee.
Last year alone, published research linked moderate coffee intake with delayed Alzheimer's onset, lowered risk of heart failure and reduced risk of basil cell carcinoma -- the most common type of skin cancer.