Childrens'Health - 90 Minutes of Exercise - A New Study

July 24, 2006 — International guidelines for physical activity for children should be increased to 90 minutes per day, according to the results of a cross-sectional study reported in the July 22 issue of The Lancet.
"Atherosclerosis develops from early childhood; physical activity could positively affect this process," write Lars Bo Andersen, MD, from the Norwegian School of Sport Sciences in Oslo, Norway, and colleagues. "This study's aim was to assess the associations of objectively measured physical activity with clustering of cardiovascular disease risk factors in children and derive guidelines on the basis of this analysis."
In this cross-sectional study, 1732 randomly selected 9-year-old and 15-year-old school children from Denmark, Estonia, and Portugal were evaluated for physical activity using accelerometry and for cardiovascular risk factors. The composite risk factor score (mean of Z scores) included systolic blood pressure, triglyceride levels, total cholesterol/high-density lipoprotein (HDL) cholesterol ratio, insulin resistance, sum of 4 skinfolds, and aerobic fitness. At-risk individuals were defined as those with a risk score 1 SD above the normal.
Compared with the most active quintile, odds ratios for having clustered risk for ascending quintiles of physical activity (counts per minute) were 3.29 (95% confidence interval [CI], 1.96 - 5.52), 3.13 (95% CI, 1.87 - 5.25), 2.51 (95% CI, 1.47 - 4.26), and 2.03 (95% CI, 1.18 - 3.50), respectively. In all analyses, risk was elevated in the first to the third quintile of physical activity. The mean time spent above 2000 counts per minute in the fourth quintile was 116 minutes per day in 9-year-old children and 88 minutes per day in 15-year-old teenagers.
Study limitations include cross-sectional design; use of a composite score; guidelines derived from these analyses only related to metabolic health and not to bone health, psychological well-being, or other dimensions of health; inability of the physical activity measure to capture cycling, swimming, and load-bearing activity; and assessment of physical activity for only 4 days.
"Physical activity is important for metabolic health in children," the authors conclude. "To prevent clustering of cardiovascular disease risk factors, physical activity levels should be higher than the current international guidelines of at least 1 h per day of physical activity of at least moderate intensity. Achieving 90 min 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 authors have disclosed no relevant financial relationships. The Danish Heart Foundation, the Danish Medical Research Council, the Danish Council for Sports Research, and the Estonian Science Foundation supported this study.
In an accompanying editorial, Ram Weiss, MD, from Hadassah Hebrew University Hospital in Jerusalem, Israel, calls this "a well-designed investigation."
"In addition to aerobic activity, resistance training might have beneficial effects on the development of lean body-mass and muscular strength, both of which might facilitate long-term participation in regular physical activity," Dr. Weiss writes. "To achieve such levels in all children, daily physical activity should be in the curriculum, with traditional athletics and enjoyable activities for different ages. The implementation of such interventions in schools should be a strong priority because physical activity represents a major disease prevention measure and can promote future beneficial lifestyle practices."