Depression can do more physical damage to a person's health than several long-term diseases, according to a study.

Saba Moussavi of the World Health Organisation led the largest population-based study on the physical effects of several illnesses by analysing data from more than 245,000 people in 60 countries. His results, published today in the Lancet, showed that depression had more impact on sufferers than angina, arthritis, asthma, and diabetes.

"On the basis of our results, addressing the further exacerbation of disability due to depression needs to be a priority of health systems worldwide," wrote Dr Moussavi. "Primary care providers must be taught not to ignore the presence of depression when patients present with a chronic physical condition."

He said that this would only be achieved by reducing the stigma around mental illness and alerting doctors and the public at large that depression was a disease at least on a par with physical chronic diseases in damaging health.

Depression was the fourth leading cause of "disease burden" in 2000, a measure of the number of years of full health lost due to an illness. Projections by scientists at the Harvard School of public health suggest that, by 2020, depression will rise to become second only to heart disease in terms of disease burden.

On a scale of 0 to 100, with 0 indicating worst health and 100 indicating best health, sufferers of depression had an average score of 72.9 in Dr Moussavi's study. This compared with 80.3 for asthmatics, 79.6 for angina sufferers, 79.3 for arthritis sufferers and 78.9 for those with diabetes. "Our main findings show that depression impairs health state to a substantially greater degree than the other diseases," Dr Moussavi said.

In addition, suffering from depression along with another chronic disease produced significantly worse health than having one or more of the chronic diseases alone. "The need for timely diagnosis and treatment of depressive disorders to reduce the burden on public health is imperative," wrote Dr Moussavi. "In many primary care settings patients presenting with multiple disorders that include depression often don't get diagnosed, and if they do often treatment is focused towards the other chronic diseases."

In an accompanying article in the Lancet, Gavin Andrews, of the University of New South Wales, said: "In Australia less than 30% of patients receive good treatment with antidepressants, cognitive behavioural therapy, and proactive maintenance care. By contrast, 80% of patients with arthritis and 90% of patients with asthma receive an acceptable standard of care."

Dr Moussavi said mental disorders often came hand-in-hand with other chronic illnesses and would become more common as the world's population lived longer.