People with bipolar disorder who smoke appear to have a heightened risk of suicidal behavior - possibly because they are generally prone to impulsive acts, a new study suggests.

Bipolar disorder, also known as manic depression, is marked by dramatic swings in mood - ranging from episodes of debilitating depression to periods of euphoric recklessness. Previous studies have found that bipolar patients who smoke have a higher suicide risk than their non-smoking counterparts, but the reasons have not been clear.

The new findings suggest that high levels of impulsivity - one of the symptoms of bipolar disorder - may draw some patients to both smoking and suicidal behavior.

Dr. Michael J. Ostacher and colleagues at Massachusetts General Hospital in Boston found that among 116 bipolar patients they followed, current smokers generally scored higher on a standard measure of suicidal thoughts and behaviors.

Moreover, smokers were more likely to make a suicide attempt over the next nine months, the researchers report in the journal Bipolar Disorders.

Five of the 31 smokers in the study (16 percent) attempted suicide during the study period. By comparison, only 3 of 85 non-smokers (3.5 percent) attempted suicide during the study.

The researchers also used a standard questionnaire to gauge patients’ impulsiveness - such as how often they speak or act without thinking and how well they plan for the future.

When those scores were factored in, the link between smoking and suicidal behavior diminished. The implication, according to Ostacher’s team, is that high levels of impulsivity partly explain why smokers were at greater risk.

From a practical standpoint, the researchers write, the findings add more evidence that smoking can be considered a “clinical marker” of higher suicide risk in bipolar patients.

Smoking, in and of itself, may not be a strong predictor of patients’ suicide odds, but doctors can still consider it as part of a comprehensive patient assessment, the researchers suggest.

It is unknown, they note, whether helping bipolar patients quit smoking would have any effect on their risk of suicidal behavior.

SOURCE: Bipolar Disorders, November 2009.