Serious mental health problems could take a greater toll on a person's life expectancy than heavy smoking, a new study suggests.

According to UK scientists, serious mental illnesses appear to reduce life expectancy by 10 to 20 years. Reduced life expectancy related to heavy smoking is eight to 10 years.

However, mental health is not prioritised in the same way as smoking is, they insisted.

They analysed the results of 20 relevant papers on these issues. These papers contained information on more than 1.7 million people and 250,000 deaths.

The scientists from Oxford University found that the average reduction in life expectancy for people with schizophrenia is between 10 and 20 years, while the average reduction related to bipolar disorder is between nine and 20 years.

Those with serious drug and alcohol abuse issues can expect a reduced life expectancy of between nine and 24 years, while those with recurrent depression can expect a reduction of between seven and 11 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," the scientists said.

They noted that there could 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," they pointed out.

However, they insisted that ‘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 healthcare and appropriate jobs and meaningful daytime activities. It'll be challenging, but it can be done," they said.

They called on governments, care providers and researchers to make mental health ‘a much higher priority for research and innovation'.

"Smoking is recognised as a huge public health problem. There are effective ways to target smoking, and with political will and funding, rates of smoking-related deaths have started to decline. We now need a similar effort in mental health," they added.

Details of these findings are published in the journal, World Psychiatry.

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