Higher BMI Not a Risk Factor for Heart Attacks Among Identical Twins

Higher body mass index (BMI) does not increase the risk of heart attacks or death, but does increase the risk of developing diabetes, according to a study of 4,046 pairs of identical twins in Sweden.

The study, “Risks of Myocardial Infarction, Death, and Diabetes in Identical Twin Pairs With Different Body Mass Indexes,” published in the Journal of the American Medical Association (JAMA), International Medicine, suggest that lifestyle changes to reduce obesity are more effective in decreasing the risk of diabetes than they are in decreasing the risk of developing cardiovascular diseases.

The team of researchers, led by Dr. Anna Nordström of Umeå University in Sweden, identified the identical twins with different BMIs using the national Swedish twin registry.

Incidence of heart attacks and deaths in heavier versus leaner twins between 1998 and 2013 were evaluated.  The average age of the twins was 57.6; the youngest pair was about 42 and the oldest pair was almost 92.

They found that 203 heart attacks and 550 deaths occurred among heavier twins, or those with a BMI of around 26; and found 209 heart attacks and 633 deaths occurred among leaner twins, or those who had a BMI of around 24.

When researchers compared twin pairs with a larger difference in BMI, when the heavier twin had a BMI of 30 or more, the risk of heart attack or death among heavier was still not higher. But when researchers analyzed the risk of developing diabetes, they found that the heavier twins were at greater risk than the leaner twins.

Finally, researchers noted that increases in BMI that occurred 30 years before baseline were not associated with the later risk of heart attack or death —  but were associated with the risk of developing diabetes.

Many studies show that high BMI, especially obesity, is a major risk factor for cardiovascular disease and death but the role of genetic factors in determining risk is not clear.

The study is one of few that compare the risk of heart attacks, type 2 diabetes, and death in identical twins who have different BMIs. Because identical twins have the same genetic makeup, scientists hope to use the approach to focus on the impact of lifestyle and body weight on risk.