When obese teen boys grow into adulthood they're more likely to develop early cardiovascular disease -- that's no surprise. But compared with the scrawny adolescents at the lowest end of teens' weight range, even those of "normal weight" are at higher risk of clogged arteries and heart attacks in young adulthood, says a new study.
The study, published in the New England Journal of Medicine on Wednesday, suggests that many teens who should be taking early steps to head off heart disease are instead waved through their yearly physicals because their body-mass index, or BMI, falls into the "normal healthy weight" category.
The same study has better news for pudgy teen boys when it comes to Type 2 diabetes: As long as they do not carry their extra weight into adulthood, they are at no higher risk of developing diabetes than kids considered underweight or normal weight.
"Everyone talks about obesity, but really, obesity is just the tip of the iceberg" when it comes to predicting an adolescent's risk for developing cardiovascular disease, said Dr. Amir Tirosh, the lead author of the study. The study tracked 37,000 teenage Israeli boys for an average of 17 years to detect how adolescent body mass influences the likelihood of developing Type 2 diabetes or cardiovascular disease in early to mid-adulthood.
"The body seems to have a longer BMI memory," said Tirosh, of Brigham and Women's Hospital's Department of Endocrinology, Diabetes and Hypertension. When it comes to heart disease risk, the effects of carrying more weight as a teen appear to persist, even if an individual becomes a lean adult. Heavy teens who remained or became heavy as adults had a predictably higher rate of Type 2 diabetes. But Tirosh said the body appeared to be more forgiving if a chubby teen became a lean adult.
Tirosh said that, compared with 17-year-old boys in the bottom tenth percentile of height and weight, boys with BMIs between 20 and 25 -- considered normal and healthy -- had rates of heart disease in their 30s and 40s that were three times higher. Young Israelis with BMIs of 25-30 -- defined as overweight but not yet obese -- were seven times more likely to develop heart disease in their 30s or 40s as those whose body-mass lay in the bottom 10% of the population range.
"We're not far from the point at which pediatricians should start to apply primary prevention approaches for kids to prevent cardiovascular disease later in life," said Tirosh. In choosing which kids to steer toward dietary and lifestyle changes, he added, pediatricians should not be complacent about youngsters whose weight is defined as normal, if they smoke, have a high lipid profile, metabolic abnormalities or have a family history of heart disease.
"The earlier we start, the better," said Tirosh. "That's a no-brainer."
Tirosh cautioned that because this large study followed only boys, it's not clear that the same dynamics will apply for teenage girls.