"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," the lead researcher Michel Lucas, research fellow in the Department of Nutrition at HSPH, said in a press statement.
According to the study researchers, apart from stimulating the central nervous system, caffeine plays the role of a mild antidepressant by enhancing the production of certain neurotransmitters in the brain that include serotonin, dopamine and noradrenaline.
This further explains the finding produced in the epidemiological studies conducted previously that reveals an association between coffee drinkers and reduced risk of depression.
In order to evaluate the correlation between coffee consumption and suicide risk in men and women, the researchers analyzed the data of 43,599 men who had participated in the Health Professionals Follow Up Study (HPFS) between 1988 and 2008. They also analyzed 73,820 women who were a part of the Nurses' Health Study (NHS) conducted between 1992 and 2008 and another set of 91,005 women who were a part of Nurses' Health study II (NHS II) between 1993 and 2007.
To proceed with the finding, the researchers assessed the participant's intake of caffeine, coffee; decaffeinated coffee was assessed every four years through questionnaires. The consumption of caffeine was calculated not just from coffee consumption but also other sources such as caffeinated soft drinks, chocolate and tea. However, they noticed that in the NHS group coffee was the major source of caffeine (80%) followed by 79% in NHS II group as well as HPFS. In the three studies they saw nearly 277 deaths that occurred due to suicide.
Despite the clear evidence obtained in this study the researchers do not recommend that the depressed adults increase caffeine consumption.
"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 400mg of caffeine/day," the study states.
In those who drank two-three to cups of coffee and in those who had four or more cups of coffee not much difference in the risk was noticed because of the small number of suicide cases in these categories.
The researchers documented their finding in The World Journal of Biological Psychiatry.