The Iowa researchers compared the body mass index of a cohort of 518 adolescents in Muscatine, Iowa, ages 15 to 18 years, from 1971 to 1981, with that of 228 of their offspring when they were the same age, in 2001 to 2003. They found that body mass index (BMI), a measure of obesity, increased from 22.97 to 24.24 among boys and from 21.9 to 24.4 among girls from 1971-1981 to 2001-2003. A BMI of 18.5 to 24.9 is considered to be normal weight, according to the National Heart, Lung, and Blood Institute.
Further analysis showed that the average BMI of teenagers in the original cohort increased by about 0.44 per year of age, compared with 1.1 per year of age in the cohort of offspring.
"That means the rate of weight gain during the teen years is now roughly double what it was," said study author Patricia H. Davis, M.D., associate professor of neurology at the University of Iowa in Iowa City. "We expected that today's teens would be somewhat more obese but were surprised by the magnitude of the change."
The study also showed that total cholesterol and blood pressure, both risk factors for cardiovascular disease, are more strongly correlated with obesity in today's teenagers than in the past, she said.
In 1971 to 1981, the correlation (a measure of the strength of the relationship) of BMI with cholesterol was 16 percent and with systolic blood pressure was 23 percent, while in 2001 to 2003, these correlations rose to 32 percent and 38 percent, respectively.
Studying teenagers and their parents allowed the researchers to remove some of the genetic components that could have explained the variability in obesity, she added.
"Obese children are at higher risk for diabetes, strokes and heart disease later in life," Davis said. "If we don't do something about this disturbing trend, the health of the nation will decline as these children get older."
Co-authors include Jeffrey D. Dawson, Sc.D., and Ronald A. Lauer, M.D.
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