Coffee Reduces Suicide Risk
Regular commenter Michael Reynolds passes on word that people who drink more coffee are less likely to kill themselves.
Harvard Gazette (“Coffee drinking tied to lower risk of suicide“):
Drinking several cups of coffee daily appears to reduce the risk of suicide in men and women by about 50 percent, according to a new study by researchers at the Harvard School of Public Health (HSPH). The study was published online July 2 in The World Journal of Biological Psychiatry.
“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, research fellow in the Department of Nutrition at HSPH.
The authors reviewed data from three large U.S. studies and found that 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.
Caffeine not only stimulates the central nervous system but may act as a mild antidepressant by boosting production of certain neurotransmitters in the brain, including serotonin, dopamine, and noradrenaline. This could explain the lower risk of depression among coffee drinkers that had been found in past epidemiological studies, the researchers reported.
In the new study, researchers examined data on 43,599 men enrolled in theHealth Professionals Follow-Up Study (HPFS) (1988-2008), 73,820 women in the Nurses’ Health Study (NHS) (1992-2008), and 91,005 women in the Nurses’ Health Study II (NHSII) (1993-2007). Caffeine, coffee, and decaffeinated coffee intake was assessed every four years by questionnaires. Caffeine consumption was calculated from coffee and other sources, including tea, caffeinated soft drinks, and chocolate. However, coffee was the major caffeine source — 80 percent for NHS, 71 percent for NHS II, and 79 percent for HPFS. Among the participants in the three studies, there were 277 deaths from suicide.
In spite of the findings, the authors do not recommend that depressed adults increase caffeine consumption, 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 authors wrote.
The study itself (“Coffee, caffeine, and risk of completed suicide: Results from three prospective cohorts of American adults“) is gated, naturally, but the methodology is summarized in the abstract:
Objective.To evaluate the association between coffee and caffeine consumption and suicide risk in three large-scale cohorts of US men and women. Methods. We accessed data of 43,599 men enrolled in the Health Professionals Follow-up Study (HPFS, 1988-2008), 73,820 women in the Nurses’ Health Study (NHS, 1992-2008), and 91,005 women in the NHS II (1993-2007). Consumption of caffeine, coffee, and decaffeinated coffee, was assessed every 4 years by validated food-frequency questionnaires. Deaths from suicide were determined by physician review of death certificates. Multivariate adjusted relative risks (RRs) were estimated with Cox proportional hazard models. Cohort specific RRs were pooled using random-effect models. Results. We documented 277 deaths from suicide. Compared to those consuming ≤ 1 cup/week of caffeinated coffee (< 8 oz/237 ml), the pooled multivariate RR (95% confidence interval [CI]) of suicide was 0.55 (0.38-0.78) for those consuming 2-3 cups/day and 0.47 (0.27-0.81) for those consuming ≥ 4 cups/day (P trend < 0.001). The pooled multivariate RR (95% CI) for suicide was 0.75 (0.63-0.90) for each increment of 2 cups/day of caffeinated coffee and 0.77 (0.63-0.93) for each increment of 300 mg/day of caffeine. Conclusions. These results from three large cohorts support an association between caffeine consumption and lower risk of suicide.
One explanation of the Cox proportional hazard model, of which I had never previously heard, is available here [PDF]. But the key takeaway is that this isn’t simply raw correlation; the researchers used a sophisticated method of isolating the effects of caffeine consumption on suicide rates from the other variables.
That’s important here in at least two ways. First, since suicide is a relatively rare event, we’re dealing with rather small numbers. Second, we want to make sure that the directionality is clear. That is, the sort of people who drink a lot of coffee might simply be less likely to kill themselves than the sort that doesn’t.