Twin with higher BMI has higher risk of diabetes but not death or MI

A cohort study of identical twins found that the twin with a higher body mass index (BMI) at baseline had a significantly increased risk of diabetes compared with the twin with a lower BMI. However, the risk of death or MI was similar in both twins.

Lead researcher Peter Nordström, PhD, of Umeå University in Sweden, and colleagues published their results online in JAMA Internal Medicine on August 1.

“Together, the results may indicate that interventions performed to promote weight loss are more effective to reduce the incidence of diabetes than to reduce the risk of [cardiovascular disease] and death,” they wrote.

The researchers evaluated 4,046 pairs of monozygotic, genetically identical twins who enrolled in the Swedish twin registry and the SALT (Screening Across Lifespan Twin Study), which screened all twins born in Sweden before 1958 for common complex disease. They conducted the study from March 17, 1998, to Jan. 16, 2003, and provided follow-up analyses through Dec. 31, 2013.

At baseline, the mean age was 57.6 years old, while the mean BMI was 25.9 in the heavier twin and 23.9 in the lighter twin. Of the twins with the higher BMI, 44.4 percent were overweight and 12.3 percent were obese compared with 28.5 percent and 3.7 percent, respectively, of twins with the lower BMI. In addition, twins with higher BMIs were less physically active and less likely to smoke, although all other baseline characteristics were similar between the groups.

After a mean follow-up period of 12.4 years, 5.0 percent of the heavier twins and 5.2 percent of the lighter twins had an MI, while 13.6 percent and 15.6 percent, respectively died.

When assessing twin pairs with a BMI difference of 7.0 or more, the risk of MI or death was not greater in heavier twins, either.

During the follow-up period, there were 345 incident cases of diabetes in the heavier twins and 224 cases in the leaner twins. After adjusting for physical activity and smoking, the odds ratio of incident diabetes was 1.94 in the heavier twins compared with the leaner twins. The risk of incident diabetes was increased in heavier twins in most subgroups, too.

The researchers added that changes in BMI approximately 30 years before baseline were associated with an increasing risk of diabetes but not of MI or death.

They also acknowledged the study had a few potential limitations, including that patients self-reported their weight and height.