Researchers found that regular smokers may be at higher risk of developing depressive symptoms comparing to people who never smoked and added another reason to the why-people-should-not-smoke list. They also found that people who have quit may be protected from depressive symptoms in the long run but at risk in the short run.

There are various hypothesis about the exact link between depressive symptoms and cigarette smoking. Some experts believe that those people who suffer from depression may smoke in order to alleviate their symptoms while others think that chronic smoking may have a role in the etiology of depression. Also, there are thoughts about shared underlying genetic factors behind this co-morbidity as well as a reciprocal mechanism.

The researchers from the Department of Public Health at the University of Helsinki decided to explore which of these hypothesis would be supported by the data when smoking behaviour and changes in it are looked as a predictor of depressive symptoms.

They used data from the Finnish Adult Twin Cohort Project. As the data consisted of twins, the researchers could test the causality between smoking and depression and to explore potential shared genetic influences underlying the association.

The results suggested that persistent chronic cigarette smoking predicted depressive symptoms, however only in men. The finding came as a surprise because nicotine is thought to have some positive effects on moods. They believe it is other substances within tobacco smoke they should be looking at.