Instant or espresso, coffee seems to ward off dark thoughts of suicide in women, a study says.
Female nurses who drank two to three cups of caffeinated coffee a day had a 66 percent lower suicide rate than those who didn't drink any, according to a study in today's edition of the American Medical Association's Archives of Internal Medicine.And those who drank more than four cups per day were 58 percent less likely to commit suicide than colleagues who drank less per day.
The study looked at 86,626 female nurses from 1980 to 1990, and found 11 cases of suicide among nurses who drank two to three cups of coffee per day, compared with 21 cases among those who said they almost never drank coffee.
The study's author, Dr. Ichiro Kawachi, cautioned the results might be skewed because doctors might tell depressed patients not to drink coffee.
The study, funded by the National Institutes of Health, also did not examine the effect of caffeine on people who attempt suicide. Ka-wachi said more study was needed.
But the findings are consistent with a 1993 Kaiser Permanente Medical Care Program study of 128,934 men and women that found a direct correlation between coffee drinking and a lower suicide rate.
Both studies also found a modest link between caffeine and reduced number of fatal motor vehicle crashes. The figures are not statistically significant but may result from fewer people using cars to commit suicide or because people who have just consumed caffeine tend to be more alert and thus crash less frequently, researchers said.
Kawachi noted that many coffee drinkers lead stressful lives as well as smoke and drink alcohol heavily.
"Coffee drinkers seem to do everything that seems to put them at risk for depression and suicide, but they are highly protected," apparently by drinking coffee, said Kawachi, of the Harvard Medical School and Brigham and Women's Hospital in Boston.
A 1990 study found that as little as 100 mg of caffeine per day could produce increased feelings of well-being, energy and motivation to work. A 5-ounce cup of coffee contains 40 to 180 mg of caffeine, according to the Food and Drug Administration.
Dr. John Greden, an expert in depression at the University of Michigan, agreed the relationship between caffeine and depression merits further study.
He said Kawachi should have examined the effect of antidepressants as well as blood pressure medication, which tends to be a depressant.