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Original Investigation
October 2016

Risks of Myocardial Infarction, Death, and Diabetes in Identical Twin Pairs With Different Body Mass Indexes

Author Affiliations
  • 1Section of Geriatrics, Department of Community Medicine and Rehabilitation, Umeå University, Umeå, Sweden
  • 2Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden
  • 3Section of Orthopedics, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden
  • 4Public Health and Clinical Medicine, Occupational and Environmental Medicine, Umeå University, Umeå, Sweden
JAMA Intern Med. 2016;176(10):1522-1529. doi:10.1001/jamainternmed.2016.4104

Importance  Observational studies have shown that obesity is a major risk factor for cardiovascular disease and death. The extent of genetic confounding in these associations is unclear.

Objective  To compare the risk of myocardial infarction (MI), type 2 diabetes, and death in monozygotic (MZ) twin pairs discordant for body mass index (BMI).

Design, Setting, and Participants  A cohort of 4046 MZ twin pairs with discordant BMIs (difference >0.01) was identified using the nationwide Swedish twin registry. The study was conducted from March 17, 1998, to January 16, 2003, with follow-up regarding incident outcomes until December 31, 2013.

Main Outcomes and Measures  The combined primary end point of death or MI and the secondary end point of incident diabetes were evaluated in heavier compared with leaner twins in a co-twin control analysis using multivariable conditional logistic regression.

Results  Mean (SD) baseline age for both cohorts was 57.6 (9.5) years (range, 41.9-91.8 years). During a mean follow-up period of 12.4 (2.5) years, 203 MIs (5.0%) and 550 deaths (13.6%) occurred among heavier twins (mean [SD] BMI, 25.9 [3.6] [calculated as weight in kilograms divided by height in meters squared]) compared with 209 MIs (5.2%) and 633 deaths (15.6%) among leaner twins (mean [SD] BMI, 23.9 [3.1]; combined multivariable adjusted odds ratio [OR], 0.75; 95% CI, 0.63-0.91). Even in twin pairs with BMI discordance of 7.0 or more (mean [SE], 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, in the total cohort of twins, the risk of incident diabetes was greater in heavier twins (OR, 2.14; 95% CI, 1.61-2.84). Finally, 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).

Conclusions and Relevance  In MZ 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.