Monozygotic twins are genetically identical so they provide a unique tool for evaluating risks associated with obesity independent of genetic factors.
A study of monozygotic Swedish twins suggests that while a higher BMI was not associated with increased risk of heart attack or death for the heavier twin, it was associated with increased risk for the onset of diabetes for that twin, suggested an article published online by JAMA Internal Medicine
‘A higher BMI was not associated with increased risk of heart attack or death for the heavier twin, but it was associated with increased risk for the onset of diabetes for that twin.’
Peter Nordstram and coauthors used a nationwide Swedish twin registry to identify 4,046 monozygotic twin pairs with discordant (differing) body mass indexes (BMIs). The study - conducted from March 1998 to January 2003 with follow-up on outcomes through 2103 - compared the risk of myocardial infarction (MI, heart attack), death and type 2 diabetes in the twin pairs.
During an average follow-up of 12.4 years, there were 203 heart attacks (5%) and 550 deaths (13.6%) among the heavier twins (average BMI 25.9) compared with 209 heart attacks (5.2%) and 633 deaths (15.6%) among leaner twins (average BMI 23.9), according to the results. Even in twin pairs where the heavier twin had a BMI of 30 or more, the risk of heart attack or death was not greater in the heavier twin. However, the risk of the onset of diabetes was greater in the heavier twins, the study reports.
Study limitations include self-reported weight and height.
"The present study was not able to verify that obesity is causally associated with an increased risk of MI or death after consideration of genetic factors. In contrast, the results revealed a significant association between obesity and diabetes after accounting for genetic factors. The association between obesity and diabetes was significantly stronger than the association with CVD [cardiovascular disease] and death. This finding may indicate that interventions to promote weight loss are more effective in reducing the risk of diabetes than the risk of CVD and mortality," the study concludes.