TUCSON, ARIZ. — There are 1.2 million previously unidentified normal-weight adolescents nationally who may be at increased risk of insulin resistance, Dr. Ann Rodden, said at the annual meeting of the North American Primary Care Research Group.
Adolescents with a body mass index (BMI) in the 75th to 84.9th percentile and those who have low levels of physical activity were at increased risk for insulin resistance, according to data obtained in a secondary analysis of the National Health and Nutrition Examination Survey (NHANES) during 1999–2002.
Prevalence estimates suggest that more than 8.5 million American adolescents have insulin resistance. Of these, more than 1.2 million are in the 75th to 84.9th BMI percentile. The American Diabetes Association considers adolescents with a BMI at or above the 85th percentile to be at risk for insulin resistance, said Dr. Rodden, department of family medicine, Medical University of South Carolina, Charleston.
“There is a population of adolescents that right now we do not consider to be at risk of insulin resistance and that we should be looking at in addition to those already identified,” she said.
The analysis was based on a nationally representative sample of 1,806 nondiabetic, nonpregnant adolescents aged 12–19 years who were participating in the NHANES study. Insulin resistance was calculated using the Homeostasis Model Assessment (HOMA) method, with a value of more than 3.16 used as the cutoff for insulin resistance.
Of these, 581 adolescents had insulin resistance, representing 30,855,840 adolescents in the U.S. population. Their mean age was 15 years. Overall, 28% of all females and 27% of all males who were evaluated had insulin resistance. Among individual ethnic groups, whites were less likely to have insulin resistance (28.2%) than were blacks (34.9%) or Hispanics (34.5%). Among those who reported physical activity levels of less than an hour a week of heavy activity, 38% had insulin resistance.
Only 9.2% of those in the under-50th BMI percentile and 13.3% in the 50th to 74.9th percentile had insulin resistance. Of note was that about one-third (33.8%) of normal-weight adolescents in the 75th to 84.9th BMI percentile had insulin resistance, as did 37.8% in the 85th to 94.9th percentile and 72.8% in the 95th or higher BMI percentile, Dr Rodden reported.
With a logistic regression analysis adjusting for age, ethnicity, gender, poverty income ratio, and carbohydrate intake, the odds of developing insulin resistance were four times higher for adolescents in the 75th to 84.9th percentile (odds ratio 4.28) and the 85th to 94.9th percentile (OR 4.30), and nearly 18 times higher for overweight adolescents in the 95th or higher percentile (OR 17.91). The risk was not significantly increased for adolescents in the two lowest BMI percentiles.
Being less active was also significantly associated with increased risk of insulin resistance, particularly among those with less than an hour a week of heavy activity (OR 4.38). But cardiovascular fitness level was not. This finding suggests that physical activity may have metabolic benefits irrespective of the level of fitness achieved, Dr. Rodden said.
The study was limited by the lack of a universally accepted definition for insulin resistance in adolescents, and self-reported physical activity data.