While studies have linked depression to a higher risk of death from heart disease, new research suggests that it may contribute to deaths from a range of causes.

In a study of more than 61,000 Norwegian adults, 2,866 showed significant depression symptoms at enrollment between August 1995 and June 1997. Compared with undepressed participants, the depressed subjects had a higher risk of death from heart disease, stroke, as well as most major causes of death, at follow-up in January 2001.

The link between depression and poorer survival held up when researchers factored the possible influence of study participants' age, medical conditions and physical complaints at the start of the study.

The findings, they investigators note, suggest that the potential consequences of depression are not limited to poorer heart health or higher suicide risk.

"We can conclude that depression is a major public health concern, with increased mortality at the level of smoking," lead study author Dr. Arnstein Mykletun, of the University of Bergen in Norway, told Reuters Health.

He and his colleagues report their findings in the journal Psychosomatic Medicine.

The study involved 61,349 men and women who completed standard measures of depression and anxiety, and reported any medical conditions and physical symptoms they had. At study follow-up, 2,309 subjects had died.

In general, depressed men and women had higher risks of death from most major causes, including heart disease, stroke, respiratory illnesses (such as pneumonia and influenza) and diseases of the nervous system (such as Parkinson's disease and multiple sclerosis).

One exception was cancer, which showed no clear relationship to depression. They also found no increased risk of death among subjects with anxiety disorders.

Researchers have speculated that depression may affect heart disease risk through direct effects on the nervous and cardiovascular systems -- by increasing inflammation in the blood vessels or the propensity of blood to clot, for instance.

It might also have an indirect impact, by raising the likelihood of unhealthy habits, like smoking, or by keeping people from sticking with treatment regimens for heart disease.

Similar indirect effects may partially explain the association between depression and other causes of death, according to Mykletun. But, he added, based on the current findings, which also took into account people's lifestyle habits, there are probably other factors at work.

More research, Mykletun said, should investigate the reasons why depression may speed death from a range of diseases.