Two to four cups of coffee a day reduces the risk of suicide in men and women by about 50 per cent, according to the findings of a new report from the US.

Lead researcher Michel Lucas and his colleagues found caffeine not only stimulates the central nervous system but may act as a mild anti-depressant by boosting production of certain neurotransmitters in the brain, including serotonin, dopamine and noradrenaline. The authors have expressed recommended adults suffering from depression to not increase their caffeine intake to counter it, as most people already consume their optimal amount. 

Researchers conducted a review of data from three previous studies involving the 43,599 men enrolled in a study from 1988-2008, 73,820 women from a study covering 1992-2008 and 91,005 women in a survey from 1993 to 2007. In the studies, caffeine, coffee and decaffeinated coffee intake was assessed every four years by questionnaires.

The Department of Nutrition at the Harvard School of Public Health has now published its review of the studies, and claimed 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.