A higher body mass index (BMI) may not put you at increased risk of heart attack or death, but it does put you at increased risk of diabetes, a Swedish study of genetically identical twins said Monday.
BMI, a measure of body fat, is calculated as weight in kilograms divided by height in meters squared. A BMI between 19 and 24 is considered normal and healthy, while a BMI between 25 and 29 is overweight, and a BMI over 30 is considered obese.
The new study, conducted from March 1998 to January 2003 with follow-up on outcomes through 2013, compared the risk of heart attack, death and type 2 diabetes in 4,046 Swedish monozygotic twin pairs, who are genetically identical.
During a follow-up period of on average 12.4 years, there were 203 heart attacks (5 percent) and 550 deaths (13.6 percent) among the heavier twins, with an average BMI of 25.9.
The numbers were similar among leaner twins with an average BMI of 23.9: 209 people, or 5.2 percent, had heart attacks and 633 people, or 15.6 percent, died.
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 reported.
"The results suggest that lifestyle changes that reduce levels of obesity do not have an effect on the risk of death and heart attack, which contradicts conventional understandings of obesity-related health risks," study author Peter Nordstrom of the Umea University, Sweden, said in a statement.
"What the study does show is that there's a strong association between obesity and diabetes, which leads us to conclude that weight reduction interventions can be more effective against diabetes than when it comes to reducing the risk of heart attack and mortality."
The findings were published in the U.S. journal JAMA Internal Medicine.
