Over 100 million Americans drink coffee every day, which has led researchers at Harvard School of Public Health (HSPH) to look more closely at the effect of coffee on our happiness. The study, which was recently released, shows an association between drinking a few cups of coffee a day and a lowered — in fact, halved — risk of suicide 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," lead researcher Michel Lucas, a research fellow in the Department of Nutrition at HSPH, said in a press statement.

The study reveals coffee's ability to protect the brain as a mild antidepressant. The caffeine in coffee not only stimulates the nervous system, but also enhances the production of certain neurotransmitters in the brain that include serotonin, dopamine, and noradrenaline.

The origin of coffee is the Ethiopian highlands, where the legend of Kaldi's coffee was born. Kaldi, a goat herder. noticed that when his goats ate unknown berries from a tree, they became hyper and restless. He tried it himself and made a drink with the berries, which he brought to the local monastery. The discovery spread like wild fire and found its way east to the Arabian Peninsula, where it was cultivated and traded. Now, over 70 countries grow trees to cultivate the beans found in coffee cherries, which makes it one of the most traded agricultural commodities and consumed beverages in the world.

Now, the Harvard study, published in The World Journal of Biological Psychiatry, shows a clear association between coffee drinkers and their reduced risk of depression and thus suicide. Researchers analyzed a large pool of data from 43,599 men who had participated in the Health Professionals Follow Up Study (HPFS) between 1988 and 2008, 73,820 women who participated in the Nurses' Health Study (NHS) between 1992 and 2008, and an additional set of 91,005 women in a second NHS study between 1993 and 2007.

Each of the 208,424 participants filled out a questionnaire every four years to assess their intake of caffeinenated coffee and decaffeinated coffee. Sources of caffeine other than coffee — from soft drinks, chocolate, and tea — were also taken into account. However, researchers found 80 percent of caffeine intake was derived from coffee consumption. Throughout all three of the studies, nearly 277 deaths by suicide were recorded, which is half as much the average non-caffeinated coffee drinkers.

According to the Centers for Disease Control and Prevention (CDC), 38,364 suicide deaths were reported in 2010, which made it the 10th leading cause of death for Americans. To put into perspective, one person dies from committing suicide every 13.7 minutes in the United States.

Despite the fact that these findings show clear evidence of a correlation between caffeinated coffee intake and lower risk of suicide, researchers do not recommend that depressed adults increase their caffeine intake, but rather seek medical attention.

"This is because most individuals adjust their caffeine intake to an optimal level for them and an increase could result in unpleasant side effects. Overall, our results suggest that there is little further benefit for consumption above two to three cups/day or 400 mg of caffeine/days," wrote the study's authors.

Indeed, a previous Finnish study found a correlation between drinking eight or nine cups every day and a higher risk of committing suicide.

Source: Lucas M, O'Reilly E, Pan A, Mirzaei F, Willett W. Coffee, caffeine, and risk of completed suicide: Results from three prospective cohorts of American adults. The World Journal of Biological Psychiatry. 2013.