American adults of a normal weight with new-onset diabetes die at a higher rate than overweight/obese adults with the same disease, according to a new Northwestern Medicine study.

The study, to be published in the Aug. 7 issue of JAMA, found that normal-weight participants experienced both significantly higher total and non-cardiovascular mortality than overweight/obese participants.

Normal-weight adults with type 2 diabetes have been understudied because those who typically develop the disease are overweight or obese. In this study about 10 percent of those with new-onset diabetes were at a normal weight at the time of ascertainment.

Being overweight is a risk factor for developing this disease, but other risk factors such as family history, ethnicity and age may play a role.

"It could be that this is a very unique subset of the population who are at a particularly high risk for mortality and diabetes, and it is possible that genetics is a factor with these individuals," said Mercedes R. Carnethon, associate professor of preventive medicine at Northwestern University Feinberg School of Medicine and first author of the study.

Older adults and nonwhite participants are more likely to experience normal-weight diabetes, according to the study.

"Many times physicians don't expect that normal-weight people have diabetes when it is quite possible that they do and could be at a high risk of mortality, particularly if they are older adults or members of a minority group," Carnethon said. "If you are of a normal weight and have new-onset diabetes, talk to your doctor about controlling your health risks, including cardiovascular risk factors."

Researchers analyzed data from five cohort studies and identified 2,625 U.S. men and women over the age of 40 who were determined to have diabetes at the start of the studies. Some of these individuals already knew they were diabetic, and others found out through their participation in the studies.

Diabetes determination was based on a fasting glucose of 126 mg/dL or greater or newly initiated diabetes medication with concurrent measurements of body mass index (BMI). A participant of normal weight had a BMI of 18.5 to 24.99, while overweight/obese participants had a BMI of 25 or greater.

With the aging and diversification of the population, cases of normal weight diabetes likely will be on the rise, Carnethon said. Future studies should focus on factors such as fat distribution and genetic types in normal-weight people with diabetes, she said.