Patients with severe mental illness, such as schizophrenia and bipolar disorder, tend to suffer from high levels of heart disease, obesity and diabetes, a study of 782 patients found.
Lack of exercise, unhealthy diet, smoking and high levels of drinking are common among such patients and could be the main reason for reduced life expectancy in the group, the University of East Anglia (UEA) study said.
Those with severe mental health issues can die an average of up to 25 years earlier than people in the general population, according to several studies.
But physical health is now thought to play a larger role in premature deaths than mental health issues such as suicide, the study in the BMC Psychiatry suggests.
Lead researcher, Professor Richard Gray, of UEA's School of Nursing and Midwifery, said: "Mental health nurses do a tough job and are compassionate and highly committed. But they do not tend to be skilled at managing the physical health of their patients."
Professor Gray said: "Since mental health workers tend to have sustained one-to-one relationships with their patients over many years, those who smoke, have a poor diet and fail to take regular exercise are having a negative influence on the lives of already vulnerable people.
"We urgently need to train our mental health workers to lead by example and intervene if their patients' physical health is deteriorating.
Dr Peter Carter, Chief Executive and General Secretary of the Royal College of Nursing, said: "Mental health nurses will recognise that, too often, patients can suffer twice over because of a combination of poor mental and physical health.
"There are some complex reasons behind this, such as the side-effects of prescription drugs, lifestyle limitations and social and economic problems.
"However, we also know that there are some excellent nurse-led initiatives, which can really make a difference to people."
"Mental health nurses know nothing about general medicine. Patients now have ECGs in an attempt to reduce the number of sudden cardiac deaths but psychiatrists don't know how to interpret the ECGs. Even though they have a computer-generated report, they ignore these and don't even inform the GPs of abnormal results - this includes abnormal blood and urine tests. It's no wonder the mentally ill die younger than the so-called 'normal people' - Mary Hall, Manchester