Some serious mental illnesses can reduce a patient's lifespan by up to two decades.

New research highlights the fact that many governments don't put enough focus on the health concerns associated with mental illness, a University of Oxford  news release reported.

About one in four people in the United Kingdom have a mental disorder while about 21 percent of British men and 19 percent of women smoke tobacco.

A research team looked at how factors such as "mental health problems, substance and alcohol abuse, dementia, autistic spectrum disorders, learning disability and childhood [behavioral] disorders," affected lifespan, the news release reported.

The average life reduction in people with bipolar disorder is between nine and 20 years and for schizophrenia it is between 10 and 20 years; the loss of years for heavy smokers is between eight and 10 years.

"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," Doctor Seena Fazel of the Department of Psychiatry at Oxford University, said in the news release.

"There are likely to be many reasons for this. High-risk [behaviors] 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," Fazel said.

The researchers hope this study will encourage a push for better treatment for those with mental disorders.

"All of this can be changed. There are effective drug and psychological treatments for mental health problems. We can improve mental health and social care provision. That means making sure people have straightforward access to health care, and appropriate jobs and meaningful daytime activities. It'll be challenging, but it can be done," Fazel said.