Coffee is, without a doubt, a favorite beverage amongst many with more than 400 billion cups consumed a year. In fact, Americans consume 350 million cups of coffee a day. Coffee lovers now have another reason to keep drinking their daily beverage, as new research from the Harvard School of Public Health (HSPH) finds that two to four cups a day can reduce the risk of suicide in both men and women.

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The researchers of the study have found that in additional to serving as a stimulant, the caffeine in coffee serves as a mild antidepressant. How so? It enhances the production of neurotransmitters such as serotonin, dopamine and noradrenaline. In fact, these findings helps explain prior epidemiological studies that found a correlation between drinking coffee and a reduced risk of depression.

"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 lead researcher Michel Lucas, a research fellow in the Department of Nutrition at HSPH, in a press statement.

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The study looked at 43,599 men--all of whom were participants in the Health Professionals Follow Up Study (HPFS) between 1988 and 2008--and  164,825--who were a part of the Nurses' Health Study (NHS) conducted between 1992 and 2008 or Nurses' Health study II (NHS II) between 1993 and 2007. The researchers looked at the subjects' caffeine intake, making sure to separate consumption from tea and other caffeinated beverages, and found the coffee correlation with a lower rate of suicide.

Even with these findings, the researchers reveal that they cannot tell at-risk patietns and depressed adults to increase their caffeine/coffee 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 400 mg of caffeine/day," the study states.

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