Exercise guidelines for children and adolescents should recommend more physical activity than they do currently, according to the authors of a new study.
“To prevent clustering of cardiovascular disease risk factors, physical activity levels should be higher than the current international guidelines of at least 1 hour per day of physical activity of at least moderate intensity,” wrote Lars Bo Andersen, Ph.D., from the Norwegian School of Sport Sciences, Oslo, and colleagues (Lancet 2006;368:299–304). “Achieving 90 minutes of daily activity might be necessary for children to prevent insulin resistance, which seems to be the central feature for clustering of cardiovascular disease risk factors.”
The cross-sectional study included data from 1,732 children aged 9 and 15 years—“on either side of puberty”—from Estonia, Denmark, and Portugal who were enrolled in the European Youth Heart Study. The researchers evaluated a combination of cardiovascular risk factors to calculate a combined risk factor score for each child. Factors that were measured included blood pressure, waist circumference, weight, height, pubertal status, skinfold thickness, cholesterol level, insulin resistance, and aerobic fitness. Each child's physical activity level was monitored with an accelerometer for 4 consecutive days.
The study found that cardiovascular risk decreased with increasing levels of physical activity, such that subjects in the most active quintile of physical activity showed the lowest risk. When compared with the most active quintile of subjects, risk in the third quintile and lower was significantly higher.
Thus, those in the least active quintile had an odds ratio of 3.29 for cardiovascular risk, those in the second quintile had an OR of 3.13, and those in the third quintile had an OR of 2.5, compared with the most active subjects. Subjects in the fourth quintile of physical activity did not have a significantly raised cardiovascular risk compared with the most active quintile. In 9-year-old children, this highest level of activity corresponded to 116 minutes, and in 15-year-olds, it corresponded to 88 minutes of moderate to vigorous intensity activity— the equivalent to a walking speed of 4 km/hour—every day.
“Whether the recommendation should be that all children ought to be as physically active as children in this quintile is a subjective judgment but the present data show consistently raised risk in the three lowest quintiles,” the authors wrote.
In an accompanying commentary, Dr. Ram Weiss and Dr. Itamar Raz from Hadassah Hebrew University Hospital in Jerusalem noted the consistency of the study's findings across all three countries and potentially different dietary habits. They also noted that the association between physical activity and cardiovascular risk “was independent of the degree of adiposity and was similar for lean and overweight children, emphasizing the effect of physical activity as an independent factor and not only as a protective measure against obesity” (Lancet 2006;368:261–2).
The study's authors noted that previous studies on which the current exercise guidelines were based depended on subjective recall of physical activity and often measured only one cardiovascular risk factor. “Clustering of cardiovascular disease risk factors has recently proven a better measure of cardiovascular health in children than single risk factors.”