Schizophrenia -- a brain disorder in which people interpret reality abnormally -- is known to be associated with a reduced life expectancy of up to 30 years.
This is largely due to the onset of Type 2 diabetes, which increases the risk of physical health disorders such as heart attack or stroke, the researchers said.
"Our findings tell us that people with early schizophrenia have already started down the road to developing diabetes, even if they haven't been diagnosed with diabetes yet," said lead author Toby Pillinger from King's College London.
The findings showed that people with long-term schizophrenia are three times more likely than the general population to have diabetes, something which has previously been attributed to poor diet and exercise habits in this group, as well as the use of antipsychotic medication.
For the study, the team examined data from 16 studies comprising 731 people with a first episode of schizophrenia and 614 people from the general population.
Blood tests revealed that people with schizophrenia had higher higher levels of insulin and insulin resistance, which increased their risk of developing Type 2 diabetes compared with healthy controls.
Other factors that may raise the risk of developing diabetes include, premature birth, low birth-weight and the stress associated with developing schizophrenia that increases the levels of cortisol -- the stress hormone.
"Our study highlights the importance of considering physical health at the onset of schizophrenia and calls for a more holistic approach to its management, combining physical and mental health," Pillinger noted.
The study was published in the journal JAMA Psychiatry.