Drinking coffee is linked to lower suicide rates, suggests a study published in The World Journal of Biological Psychiatry.
Researchers from the Harvard School of Public Health (HSPH) reviewed data from three large US studies. This consisted of 43,599 men involved in the Health Professionals Follow-up study (HPFS), 73,820 women in the Nurses' Health Study (NHS) and 91,005 women in the NHS II.
The researchers analyzed data regarding consumption of caffeine, coffee and decaffeinated coffee every 4 years through food-frequency questionnaires, while the deaths from suicide were analyzed by physician review of death certificates.
The amount of caffeine consumption was assessed from both coffee and non-coffee sources, including chocolate, tea and caffeinated soft drinks. But the researchers add that coffee was the main source, accounting for a minimum of 71% in all three studies.
Over the study period, 277 deaths were a result of suicide.
Results revealed that the risk of suicide for adults who drank between 2-4 cups of coffee each day was 50% lower when compared with adults who drank decaffeinated coffee, very little or no coffee.
The researchers reported that there were no major differences in the risk of suicide between those who consumed 2-3 cups of coffee per day and those who drank 4 or more cups per day, but they note that this may be due to a smaller number of suicides in these categories.
Researchers on this study say that the risk of suicide was 50% lower in adults who drank 2-4 cups of coffee each day. However, a previous study suggested heightened depression in adults who drank 4 or more cups of coffee per day.
However, the study notes that a previous study from HSPH analyzing how coffee was related to depression revealed that researchers saw a heightened depression effect in those who drank 4 or more cups per day.
The researchers report that as well as stimulating the central nervous system, caffeine acts as a mild anti-depressant by boosting the production of particular neurotransmitters in the brain. These include noradrenaline, dopamine, and serotonin. They add that this could explain the results of studies in the past that have linked the consumption of coffee to a lower risk of depression.
Regardless of the study's results, the authors say this does not mean the consumption of coffee should be increased.
The recommended coffee intake for the average healthy adult is around 2-4 cups per day. Experts advise that too much caffeine can have unpleasant side effects, such as insomnia, nervousness, restlessness, muscle tremors and a fast heartbeat.