A new study has found mental illness sufferers in Australia are dying up to 16 years earlier than the general population, with most deaths due to disease rather than accidents or suicide.

A University of Queensland team followed 300,000 people in Western Australia who were diagnosed with mental illnesses, and compared health experiences and death rates to the general population over a 20-year period.

Diagnoses included alcohol and drug disorders, schizophrenia, psychoses, neurotic disorders, depressive, and other mental health disorders.

The study found the overall gap in life expectancy was 15.9 years for men and 12 years for women.

Patients with alcohol or drug disorders had the lowest life expectancy, with a gap of more than 20 years.

Dr Steve Kisely from UQ's School of Population Health has told the ABC most deaths are due to physical causes such as cardiovascular disease and cancer, rather than suicide or accidents.

He says people with a mental illness may sometimes miss early signs of illness or have worse access to specialised treatment.

"For instance, people who have breast cancer or colon cancer diagnosed - people with a mental health problem have actually less of a chance of getting the operation than someone with the same disorder who didn't have a mental health problem," he said.

Gap widens

Dr Kisely says the gap is worse than for smokers and similar to Indigenous Australians, but receives far less attention.

"There has been a very understandable focus in terms of closing the gap of life expectancy between Indigenous Australians and non-Indigenous Australians," Dr Kisely said.

"But the gap for people with mental illness is even greater - people still think of increased mortality as due to suicide."

"Obviously we need to address suicide, but we're dealing with a problem that's nearly 10 times as great as suicide and there isn't nearly the same amount of attention given to it."

The study also found the differential in the gap increased by about two years between 1985 and 2005.

"Whatever we're doing, we're doing it worse, rather than better," Dr Kisely said.

Dr Kisely says closing the gap for people with mental illness requires a multi-faceted approach.

Lifestyle factors

He says lifestyle factors are an important first step.

"We know that with people with schizophrenia, about 90 per cent of them will smoke and will spend about 40 per cent of their disposable income on tobacco products," he said.

"Clearly helping people to stop smoking would be a great help."

He says the next thing is to make sure people are registered with their general practitioner and see them regularly.

"We also need to encourage family doctors to have a high index of suspicion when people with a chronic mental illness come to them with new symptoms," he said.

"Don't attribute them to their underlying mental illness, but explore more to see if it's the start of a new medical condition.

"Lastly, when a problem is recognised, ensure they get the right specialist treatment."