Effects of weight on kids' heart rate vary by income

Tue May 11, 2010 1:16pm EDT
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By Amy Norton

NEW YORK (Reuters Health) - Overweight children from lower- and middle-income neighborhoods may fall short of their thinner peers in one measure of cardiovascular fitness -- but the same may not be true of those from more affluent areas, a new study suggests.

Researchers found that among 480 children and teenagers who underwent treadmill exercise tests, those with a high body mass index (BMI) tended to have a slower heart rate recovery after their workout -- but only if they were from lower- or middle-income neighborhoods.

Extra pounds did not generally seem to affect heart rate recovery among kids from the highest-income areas, the study found.

Heart rate recovery refers to the amount of time it takes a person's heart rate to return to its resting rate after a bout of exercise. It is one measure of cardiovascular fitness.

It's not certain why a high BMI would affect kids' heart rate recovery differently based on income, but there are a couple potential explanations, according to lead researcher Dr. Tajinder P. Singh, of Children's Hospital Boston.

One has to do with how BMI is calculated, he told Reuters Health in an email.

BMI is a measure of weight in relation to height, but it does not differentiate between weight from body fat and weight from muscle. It's possible, Singh said, that children and teens from more advantaged families were more likely than their peers to have a high BMI because of muscle mass.

Another potential explanation, Singh speculated, is that kids from affluent neighborhoods have healthier lifestyles -- better diets, more opportunities for exercise -- so that even if they are overweight, they may be in good health.   Continued...