High BMI Increases Risk of Diabetes, Not MI or Premature Mortality

Independent of genetic factors, higher body mass index (BMI) is associated with a higher risk of type 2 diabetes, but not of myocardial infarction (MI) or death, suggests a twin study in JAMA Internal Medicine.

Using the Swedish national twin registry, the researchers identified 4046 monozygotic twin pairs discordant for BMI. Mean BMI was 25.9 in the heavier twins versus 23.9 in the leaner twins; because the twins were genetically identical, the difference in BMI was lifestyle-related. Twelve-year follow-up data were used to estimate the effects of higher BMI on mortality and MI risk (composite primary outcome) and incident diabetes (secondary outcome).

During follow-up, MI occurred in 5.0 percent of the heavier twins and 5.6 percent of the leaner twins; mortality was 13.6 and 15.6 percent, respectively. On multivariable analysis, risk of the composite outcome was significantly lower in the heavier twins: adjusted odds ratio (OR) 0.75. On analysis of 65 twin pairs with at least a seven-unit discrepancy in BMI and where the heavier twin had a BMI of 30 or higher, the difference in MI risk or mortality was not significant.

However, incident diabetes risk was twice as high in the heavier versus leaner twins: OR 2.14. This risk increased with widening BMI discordance between pairs. Changes in BMI occurring about three decades before baseline were also unrelated to MI or mortality, but were significantly related to diabetes risk: OR 1.13.

Genetic factors may help to explain why population rates of MI and mortality are decreasing even as the prevalence of obesity increases. This study shows that lifestyle-related increases in BMI are associated with the incidence of diabetes, but not with MI or death.

Obesity appears to have a causal association with type 2 diabetes, with no confounding influence of genetics. “Lifestyle interventions to reduce obesity may be more effective in reducing the risk of diabetes than the risk of cardiovascular disease or death,” the researchers conclude. [Nordström P, et al. Risk of myocardial infarction, death, and diabetes in identical twin pairs with different body mass indexes. JAMA Intern Med 2016; doi:10.1001/jamainternmed.2016.4104].