NEJM: Even 'normal' BMI during adolescence raises chance of CV risk

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When adolescent men have elevated body mass indexes (BMI) it increases their risk for obesity-related disorders later in life, according to a study published April 7 in the New England Journal of Medicine. And despite the fact that diabetes has been linked to an increased BMI at the time of diagnosis, coronary heart disease is associated with a heightened BMI in adolescence and in adulthood, even when BMI may be in the so called "normal" range.

“Although obesity in adulthood is a well-documented risk factor for both type 2 diabetes and coronary heart disease, it remains unclear whether a longer history of relative overweight, starting earlier in life, poses an additional risk,” the authors wrote. “Furthermore, whereas the trajectory of weight and height from birth to adolescence is well documented, the progression of body mass index (BMI) from adolescence into adulthood is less well described.”

Amir Tirish, MD, PhD, of Brigham and Women’s Hospital and the Harvard Medical School in Boston, and colleagues followed 37,674 healthy young men for incident of coronary heart disease and diabetes through the Staff Examination Center of the Israeli Army Medical Corps. Weight, height and blood pressure were measured. The men had an average age of 17.44 years and the mean BMI ranged from 17.3 to 27.6.

Tirish et al reported that after almost 650,000 person-years of follow-up, 1,173 incidence cases of type 2 diabetes and 327 cases of angiography-proven coronary heart disease occurred in men between the ages of 25 and 45.

When the researchers modeled adolescent BMI as a continuous variable in a multivariate model—which adjusted for age, family history, blood pressure, life style factors, biomarkers and increased BMI— the risk of diabetes increased by 9.8 percent for each increment in one BMI unit, when this same model was used the risk of coronary heart disease increased by 12 percent for each increment in one BMI unit.

“After adjustment of the BMI values as continuous variables in multivariate models, only elevated BMI in adulthood was significantly associated with diabetes,” the authors reported. However, an elevated BMI in adolescence and adulthood was independently associated with coronary heart disease.

“The risk of coronary heart disease is associated with an elevated BMI both in adolescence and in adulthood, supporting the hypothesis that the processes causing incident coronary heart disease, particularly atherosclerosis, are more gradual than those resulting in incident diabetes,” the authors concluded.

The authors said that the results of the current study may help redefine what is often considered a “normal” or “healthy” BMI in adolescence.

The limitations of the study may come from the fact that boys who were 17 years old may not have hit puberty during the study or reached their final height, possibly construing body composition and results.

Surprisingly the authors found that men in the lowest decile for adolescent BMI had a higher risk of acquiring future diabetes. The authors said this could be due to the fact that diabetes represents a “more functional pathomechanism than coronary heart disease, which relies on anatomical changes (atherosclerosis).”

The authors said that this finding provides evidence of the fact that even incidence of clinical diabetes is reversible when lifestyle or surgical interventions take place. However, atherosclerosis can be reversed by dietary intervention, but only if that intervention takes place before the “clinical horizon” of the disease.

“In conclusion, BMI at the age of 17 years is an independent predictor of coronary heart disease in young adulthood, even when it is well within what is now defined as the normal range of BMI, suggesting that body mass has long-term consequences.”