Young men who have insomnia are more likely to suffer from depression when they hit middle age, a new study suggests. Male medical students who said they had problems sleeping were twice as likely to be clinically depressed 30 years later when compared with their peers who had no trouble falling asleep.

About 10% to 35% of the population suffers from insomnia in any given year, and the inability to sleep has long been linked to depression. Studies have shown that depression is the most common link to chronic insomnia in people who seek treatment for the problem. However, it is not clear whether insomnia is the cause or an effect of depression.

American Journal of Epidemiology (1997;146:105-114)