Depression takes a bigger toll on overall health than the chronic diseases angina, arthritis, asthma and diabetes, according to a new study in this week's edition of The Lancet.

The study's researchers also concluded that if people are ill, depression makes the sickness worse.

"Our main findings show that depression impairs health state to a substantially greater degree than the other diseases," World Health Organization researcher Dr Somnath Chatterji and colleagues wrote in the Lancet medical journal.

For the analysis, researchers studied data from 245,404 people included in WHO's World Health Survey.

After adjusting for socioeconomic factors and health conditions, depression had the largest effect on worsening health compared with the other chronic conditions.

Consistently across countries and different demographic characteristics, people with depression plus one or more chronic diseases had the worst health scores of all the disease states, researchers said.

In an accompanying comment to the study, professor Gavin Andrews and Dr Nickolai Titov, of the Clinical Research Unit for Anxiety and Depression at the University of New South Wales at St. Vincent's Hospital in Sydney, Australia, said some of the problem stems from inadequate treatment of depression in comparison to other chronic diseases.

"Treatment for depression should at least be on a par with that for other chronic diseases," they wrote.