Serious mental illnesses reduce life expectancy by 10-20 years - a loss of years that's equivalent to or worse than that for heavy smoking, a new Oxford study has warned.
Despite these stark figures and the similar prevalence of problems, mental health has not seen the same public health priority, researchers said.
The figures should galvanise governments and health and social services to put a much higher priority on how mental health services can prevent early deaths, according to Oxford University psychiatrists.
Researchers searched for the best systematic reviews of clinical studies which reported mortality risk for a whole range of diagnoses - mental health problems, substance and alcohol abuse, dementia, autistic spectrum disorders, learning disability and childhood behavioural disorders.
Twenty review papers were identified, including over 1.7 million individuals and over 250,000 deaths.
The average reduction in life expectancy in people with bipolar disorder was found to be between 9 and 20 years, it's 10-20 years for schizophrenia, between 9 and 24 years for drug and alcohol abuse, and around 7-11 years for recurrent depression.
The loss of years among heavy smokers is 8-10 years, researchers said.
All diagnoses studied showed an increase in mortality risk, though the size of the risk varied greatly. Many had risks equivalent to or higher than heavy smoking.
"We found that many mental health diagnoses are associated with a drop in life expectancy as great as that associated with smoking 20 or more cigarettes a day," said Seena Fazel of the Department of Psychiatry at Oxford.
"There are likely to be many reasons for this. High-risk behaviours are common in psychiatric patients, especially drug and alcohol abuse, and they are more likely to die by suicide. The stigma surrounding mental health may mean people aren't treated as well for physical health problems when they do see a doctor," said Fazel.
One problem is the tendency to separate mental and physical illness, said Fazel.
The finding was published in the journal World Psychiatry.