People who suffer from psychotic disorders who are also obese have decades shaved from their lifespan, says a study from Florida Atlantic University.

Obese people with bipolar disorder have lifespans 10 years shorter than average, and the lives of those who have schizophrenia are 20 years shorter.

But why? In a new study, researchers show that expanding waistlines and the way body fat is distributed are largely to blame.

Martin T. Strassnig, M.D. and his colleagues used data obtained from a 20-year study of people admitted to the hospital with a psychotic condition for the first time in the early 1990s. Study participants ranged in age from 15 to 60 years. Patients with a psychosis related to depression, substance use and other psychoses were excluded.

For the study, the researchers looked at weight and height measurements as well as biomarkers such as blood pressure, cholesterol, triglycerides, hemoglobin A1C, body fat percentage, and waist circumference. Weight gain was defined by a standard measure of BMI.

The researchers found that cholesterol, triglycerides, hemoglobin A1C, and blood pressure were not correlated with BMI in the group as a whole, but waist circumference at year 20 was significantly higher in patients with schizophrenia, and women with the mental condition had higher waist circumferences than men or women with bipolar disorder

Results also show that nearly two-thirds of those with schizophrenia and more than half of those with bipolar disorder were obese 20 years after their first hospitalization for psychosis.

Being overweight at the beginning of the study period predicted future weight gain: A large majority of people who were overweight at year two were obese at the 20-year mark. The schizophrenia group gained twice as much weight within the first 10 years, while those with bipolar disorder experienced less weight gain during the initial 10-year period compared to the subsequent 10 years.

According to Strassnig, the use of antipsychotic medication didn't appear to influence weight gain. "In fact, during years 10 to 20, when the likelihood of being exposed to the group of weight gain-causing second-generation drugs was greatest, there is evidence of plateauing of weight gain."

The researchers noted that because weight gain continues over a long period of time, interventions can be effective in avoiding further weight gain even many years into treatment. The also stressed that waist circumference should be measured frequently, especially in women with schizophrenia.

Two earlier studies from Johns Hopkins found that people with a serious mental illness, such as schizophrenia and bipolar disorder, are much more likely to develop cancer. Patients with schizophrenia were 4.5 times more likely to develop lung cancer, 3.5 times more likely to develop colon cancer, and almost three times as likely to develop breast cancer. Those with bipolar disorder had similar increases in risk.

Patients with mental problems are also more likely to be injured. Over a seven-year period, 43 percent of mentally ill people in a study were seen at an emergency room or admitted to the hospital with an injury. Of those injured, 42 percent were injured once, 23 percent twice, 25 percent three to five times, and 10 percent were injured six or more times.