Women who drink coffee are less likely to commit suicide than those who do not, suggests a study being published Monday.

The author cautions, however, that the results may not be significant because doctors might have told depressed patients not to drink coffee, a factor that wasn't studied.The study of 86,626 female nurses from 1980 to 1990 found 11 suicides among those who drank two to three cups of coffee per day, compared with 21 cases among colleagues who said they almost never drank coffee.

"Coffee drinkers seem to do everything that seems to put them at risk for depression and suicide, but they are highly protected," said the study author, Dr. Ichiro Kawachi of Harvard Medical School and Brigham and Women's Hospital in Boston.

He noted that many coffee drinkers lead stressful lives and smoke and drink alcohol heavily.

Kawachi's study did not examine whether respondents were told not to drink coffee, nor did it question the effect of caffeine on people who attempt suicide. Kawachi said the issues merit further study.

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 five-ounce cup of coffee contains 40 to 180 mg of caffeine, according to the Food and Drug Administration.

Kawachi's study was criticized by Dr. John Greden, an expert in depression at the University of Michigan.

He said researchers should have examined the effect of antidepressants and blood pressure medication, which tends to be a depressant.