BMI and Risks of MI, Death, and Diabetes in Identical Twins

Study Questions:

Is the risk of myocardial infarction (MI), type 2 diabetes (DM), and death influenced by discordant body mass index (BMI) among monozygotic twin pairs?


Data from a large cohort of monozygotic twin pairs (n = 4,046) with discordant BMIs were used for the present study. Twins were identified using the nationwide Swedish twin registry. The study was conducted between March 1998 and January 2003, with follow-up through December 2013. The primary outcomes of interest were death or MI. Secondary outcomes included incident DM.


A total of 4,046 monozygotic twin pairs were included. Mean age at baseline was 57.6 years (range, 41.9-91.8 years). Over a mean follow-up period of 12.4 years, 203 MIs (5.0%) occurred among heavier twins (mean BMI, 25.9 kg/m2) compared with 209 MIs (5.2%) among leaner twins (mean BMI, 23.9 kg/m2). For mortality, 550 deaths (13.6%) occurred among heavier twins compared with 633 deaths (15.6%) among leaner twins. The combined multivariable adjusted odds ratio (OR) was 0.75 (95% confidence interval [CI], 0.63-0.91). Even in twin pairs with BMI discordance of 7.0 or more (mean [standard error], 9.3 [0.7]), where the heavier twin had a BMI of 30.0 or more (n = 65 pairs), the risk of MI or death was not greater in heavier twins (OR, 0.42; 95% CI, 0.15-1.18). In contrast, the risk of incident diabetes was greater in heavier twins (OR, 2.14; 95% CI, 1.61-2.84). Increases in BMI since 30 years before baseline were not associated with the later risk of MI or death (OR, 0.97; 95% CI, 0.89-1.05), but were associated with the risk of incident diabetes (OR, 1.13; 95% CI, 1.01-1.26).


The investigators concluded that in monozygotic twin pairs, higher BMI was not associated with an increased risk of MI or death, but was associated with the onset of diabetes. These results may suggest that lifestyle interventions to reduce obesity are more effective in decreasing the risk of diabetes than the risk of cardiovascular disease or death.


These data support the hypothesis that BMI is associated with risk for diabetes, but does not appear to suggest BMI is associated with MI or mortality when genetic factors are equivalent, as in monozygotic twin pairs.

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