Depression is as much of a risk factor for death as smoking, according to a new study.
Utilising a unique link between a survey of over 60,000 people and a comprehensive mortality database, researchers at the University of Bergen, Norway, and the Institute of Psychiatry (IoP) at King's College London found that over the four years following the survey, the mortality risk was increased to a similar extent in people who were depressed as in people who were smokers.
Study's lead author Dr Robert Stewart has explained the possible reasons that may underlie these surprising findings.
"Unlike smoking, we don't know how causal the association with depression is but it does suggest that more attention should be paid to this link because the association persisted after adjusting for many other factors," he said.
The study also showed that patients with depression face an overall increased risk of mortality, while a combination of depression and anxiety in patients lowers mortality compared with depression alone.
"One of the main messages from this research is that 'a little anxiety may be good for you," Stewart said.
"It appears that we're talking about two risk groups here. People with very high levels of anxiety symptoms may be naturally more vulnerable due to stress, for example through the effects stress has on cardiovascular outcomes.
"On the other hand, people who score very low on anxiety measures, i.e. those who deny any symptoms at all, may be people who also tend not to seek help for physical conditions, or they may be people who tend to take risks. This would explain the higher mortality," he added.
The study has been published in The British Journal of Psychiatry.