Long-Term Study Backs Link Between Smoking, Suicidality

While Americans worry about whether cigarette smoking will cause lung cancer, perhaps they should also pay attention to a lesser-known risk factor for the habit—suicide. Epidemiological studies going back at least a quarter century have linked cigarette smoking with suicide. And now another large epidemiological study does as well.

This latest investigation was headed by Naomi Breslau, Ph.D., a professor of epidemiology at Michigan State University. Results appeared in the March Archives of General Psychiatry.

In 1988, Breslau and her colleagues selected some 1,000 young adults to participate in their study. All were members of a health maintenance organization in the Detroit area. All were interviewed at baseline and at three, five, and 10 years after the study started. During each interview, their psychiatric health, smoking habits, and occurrence of suicidal thoughts and of suicidal attempts since the last interview were ascertained.

As it turned out, subjects reported only 19 suicide attempts during the 10-year study period. Since 19 suicide attempts were not enough for a meaningful statistical analysis, Breslau and her team decided to lump suicidal attempts and suicidal thoughts together. Combining these gave 17 suicide attempts with the reporting of suicidal thoughts; two suicide attempts without the reporting of suicidal thoughts; and 130 suicidal thoughts without suicide attempts, for a total 132 suicidal thoughts and/or attempts.

Breslau and her colleagues then attempted to see whether smoking at baseline, at the three-year assessment, and at the five-year assessment could be statistically linked with the combined number of suicidal thoughts or attempts during the subsequent study periods.

The answer was yes. Compared with subjects who had never smoked, current smokers (those who had smoked during the past 12 months) were at a statistically significant increased risk of suicidal thoughts or attempts. In contrast, past daily smokers were not at increased risk for subsequent occurrence of suicidal thoughts or attempts.

Moreover, this link between current cigarette smoking and suicidal thoughts or attempts held even when potentially confounding factors—prior suicidal thoughts or attempts, current or past major depression, and current or past substance abuse—were taken into consideration.

And even though the study results did not find current cigarette smoking to be as grave a risk factor for suicidal thoughts or attempts as prior suicidal thoughts or attempts, or current or past major depression, they do suggest some practical implications.

“Clinical psychiatrists should always be concerned and inquire about suicidality, self-destructive thoughts, et cetera,” Glenn Davis, M.D., a professor of psychiatry at Michigan State University and one of the study authors, said in an interview. “But with added knowledge that there is a connection between smoking and risk for suicidal behavior, they should be particularly sensitive to smoking history in their evaluation of patients.”

“By highlighting current smoking, [this study further reinforces] the benefits of smoking cessation,” Donald Klein, M.D., a professor of psychiatry at Columbia University, pointed out to Psychiatric News.

How current cigarette smoking might trigger suicidal thoughts or attempts is not known. Yet if it does play a causal role, Breslau and her team suspect that it may do so via an intermediary culprit—the enzyme monoamine oxidase (MAO), which is found in the liver and the central nervous system. It is crucial to the functions of the neurotransmitter serotonin. Low levels of MAO have been found in blood cells of current cigarette smokers, but not in those of ex-smokers, and low blood-cell levels of MAO in turn have been linked with violence and suicide.

This investigation has several advantages over past ones on the subject. It took major depression, a well-established risk factor for suicide, into consideration, and it was quite sophisticated in design. Klein explained that it “incorporated major methodological advances by using prospective multiwave longitudinal psychiatric diagnoses in estimating whether smoking independently increases suicide-related behaviors.”

The study had a weakness, however, which Breslau and her group acknowledged in their report: The researchers did not gather data about subjects' completed suicides, only about their suicidal thoughts and attempts.

The study was funded by the National Institute of Mental Health.

An abstract of “Smoking and the Risk of Suicidal Behavior” is posted online at<http://archpsyc.ama-assn.org/cgi/content/abstract/62/3/328>.▪