May 11, 2010 / 5:19 PM / 8 years ago

Effects of weight on kids' heart rate vary by income

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.

Whatever the reasons for the findings, Singh said they suggest that lower- to middle-income children stand to gain the most from losing excess weight.

The findings, published in the Archives of Pediatrics & Adolescent Medicine, are based on the records of 480 children who underwent exercise testing at Children’s Hospital Boston because of symptoms such as breathlessness and heart palpitations during physical activity. The tests were done to rule out heart disease, and all of the children had normal results.

Singh’s team divided the children into three groups based on the socioeconomics of their neighborhoods. In the most affluent neighborhoods, the median household income was just over $100,000, and two-thirds of residents older than 25 had a college degree. In the least advantaged neighborhoods, the median income was $40,000, and 19 percent of residents older than 25 had a college degree.

Of all 480 children and teens, 70 percent had a normal BMI while the rest had a high BMI -- with 17 percent falling into the “overweight” BMI category and 13 percent into the obese category.

Heart rate recovery was measured one minute after the children completed their exercise tests. Overall, Singh’s team found that in the lower- and middle-income groups, overweight kids were slower to return to their pre-exercise heart rate than their normal-BMI counterparts.

On the other hand, normal-weight kids had similar heart rate recovery results regardless of socioeconomics.

One implication of the findings, Singh said, is that “children who have normal weight are likely to have good cardiovascular health irrespective of their socioeconomic position.”

Another, he added, is that while weight loss is important for all kids who are overweight or obese, it may be “most immediately beneficial” for those from lower- to middle-income families.

Studies in adults have linked slower heart rate recovery to a higher risk of heart disease. But there are no studies on whether slower recovery in children predicts an increased risk of heart problems later in life.

SOURCE: Archives of Pediatrics & Adolescent Medicine, May 2010.

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