The government’s recommendation for kids’ daily exercise may be too low for optimal heart health, a new study shows.

The report, published in The Lancet, suggests kids may need 90 minutes of daily physical activity to help avoid a cluster of heart disease risk factors.

That’s 30 minutes longer than the CDC’s current recommendation. The CDC says children should get at least an hour of moderate physical activity most days of the week, and preferably daily.

Kids’ physical activity needn’t be hard-core exercise. Walking and playing will do, note Lars Bo Andersen, PhD, and colleagues. Andersen is a sports medicine professor at the Norwegian School of Sport Sciences in Oslo, Norway.

Also, the findings aren’t just for overweight kids. Fitness is the issue, not fatness, a journal editorial notes.

Kids Need an Hour of Exercise a Day

Monitoring Kids’ Movement

The researchers studied 915 girls and 817 boys in three European countries: Estonia, Denmark, and Portugal.

The kids were either 9 years old or 15 years old. The researchers chose those ages because they fall either before or after puberty typically starts.

Many studies on this subject rely on kids or parents to report physical activity. But such reports aren’t always accurate. So Andersen’s team took a different approach.

The researchers gave each child a device called an accelerometer, which tracks physical activity. The kids wore the devices on their hips for two weekdays and two weekend days.

Data was also collected on the kids’ height, weight, pubertal status, blood pressure, and skinfold thickness (a gauge of body fat). The kids provided blood samples -- which were checked for cholesterol and triglycerides (a type of blood fat) -- and they took a blood sugar test after fasting.

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Big-Time Movers Fared Best

The most active kids in the group were the 9-year-olds who got about nearly two hours per day of physical activity and 15-year-olds who got nearly and hour and a half of daily physical activity.

Those children did moderate and vigorous activity that equaled walking nearly 2.5 miles per hour, the study shows.

Kids who were less physically active were two to three times more likely to have a cluster of heart disease risk factors that included higher blood pressure, poor cholesterol and triglyceride levels, thicker skinfold measurements, and resistance to insulin (the hormone that controls blood sugar).

The researchers aren’t saying any of the kids actually had heart disease. But they write that “even if none of the participants had clinical disease, clustered risk is certainly an undesirable condition, and has been shown to track into young adulthood.”

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Take-Home Message

Based on the activity level in the most active kids, Andersen and colleagues write that “achieving 90 minutes of daily physical activity might be necessary for children to prevent insulin resistance, which seems to be the central feature for the clustering of cardiovascular disease risk factors.”

A journal editorial notes that the “amount and type of physical activity needed in childhood and adolescence is still a matter of debate.”

But at least an hour “or even more on the basis of Andersen’s study, seems to be appropriate,” write the editorialists. They include Ram Weiss, MD, PhD, senior pediatric endocrinologist at Jerusalem’s Hadassah Hebrew University School of Medicine.

It would be easier for kids to reach that goal if physical activity was part of school schedules, write Weiss and colleagues.

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Fitness Is the Key

The study’s results were “similar for lean and overweight children,” the editorialists point out.

That means physical activity doesn’t just affect kids’ weight. Being active appears to have other favorable effects against heart disease risk factors, write Weiss and colleagues.

Andersen’s study has some limits. The children were studied only briefly. So it’s not clear which kids, if any, grew up to have heart disease, or which came first: better heart health or higher physical activity levels.

Still, the study was “well-designed,” with objective data from the accelerometers, note Weiss and colleagues.

By Miranda Hitti, Reviewed by Louise Chang, MD

SOURCES: Andersen, L. The Lancet, July 22, 2006; vol 368: pp 299-304. CDC: “Physical Activity for Everyone: Recommendations: Are There Special Recommendations for Young People?” Weiss, R. The Lancet, July 22, 2006; vol 368: pp 261-262. News release, The Lancet.