Researchers at Northwestern University in Chicago reviewed the data of five previous studies involving 2,625 patients older than 40 and divided nearly equally between men and women. About 12% of them were considered "normal weight."

In what is called the "obesity paradox," the data, published Wednesday in the Journal of the American Medical Association, showed a higher rate of mortality among people who were normal weight at the time of adult-onset diabetes.

Overall, the death rate in thin patients was 2.8% per year, compared with 1.5% in overweight and obese patients.
The researchers aren't sure how to explain why being overweight - one of the most common risk factors for developing Type 2 diabetes - also seems to have a protective effect against early death.

They theorize that genetics might play a role, or perhaps the way fat tissue is distributed in the body, but more research is needed to test these, and other, hypotheses.

About three million Canadians have diabetes and another six million have prediabetes (half of whom will develop the disease), according to the Canadian Diabetes Association.