New research from The Australian National University (ANU) has found that men who are diagnosed with a mental health condition in their lifetime can expect to live 10.2 years less than those who aren't, and women 7.3 years.
Lead researcher Associate Professor Annette Erlangsen said the study, which analysed medical and hospital data from Denmark over two decades from 1994-2014, also found the 'mortality-gap' had stayed consistent, despite efforts to address the issue.
"Ten years of life expectancy are lost for those with mental illness," she said.
"It is worrisome that the mortality gap between people with mental disorders and the general population has not decreased over the past decades - despite our efforts to address suicide prevention and other relevant factors."
Associate Professor Vladimir Canudas-Romo of the ANU School of Demography said while suicide, homicide and accidents (such as car crashes) were major contributing factors in the gap, those causes of death had seen some decline over the 20 year period.
He was surprised, however, to see that the gap in years lost between people with and without mental disorders doubled for deaths due to cancer and cardio-vascular disease.
"Overall the mortality gap has stayed the same, but the causes of death have changed," he said.
"Cancer and health issues such as diabetes and heart disease are now playing a bigger role."
Associate Professor Canudas-Romo also said it was concerning to see a marked increase in the number of alcohol related deaths.
"That was an eye opener," he said.
"Deaths involving alcohol still account for the major share of the life years lost among people with mental disorders over the past two decades," Associate Professor Canudas-Romo said.
The research team has called on governments to address the mortality gap by implementing more holistic approaches to dealing with mental illness.
"It is not enough to be simply prescribing some medicine and sending them on their way," he said.
Associate Professor Canudas-Romo is currently exploring the prospect of replicating the study in Australia.
Lead author Associate Professor Erlangsen is based at the Danish Research Institute for Suicide Prevention and is also affiliated to the ANU Centre for Mental Health Research.
The article has been published in The Lancet Psychiatry.