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Regardless of Sedentary Time, Exercise Improves Risk Factors

Children and adolescents participating in moderate to vigorous physical activity have a lower cardiometabolic risk profile. Moderate-to-vigorous-intensity physical activity was associated with improvements in waist circumference, systolic blood pressure, triglycerides, HDL cholesterol, and insulin in participants regardless of the amount of time they spend sedentary….

Led by Dr. Ulf Ekelund (MRC Epidemiology Unit, Cambridge, UK), researchers say that children should be encouraged to increase their participation in physical activity based on the findings rather than decrease the amount of time they spend sedentary, “as this appears more important in relation to cardiometabolic health.”

The study included pooled data from 14 studies conducted between 1998 and 2009 that were taken from the International Children’s Accelerometry Database (ICAD). In their paper, the researchers explain that the time spent in moderate to vigorous physical activity has a weak to moderate association with the amount of time children spend sedentary, and this had suggested that both variables might be independently associated with cardiometabolic risk.

Dr. Aaron Baggish (Massachusetts General Hospital, Boston), who was not affiliated with the ICAD analysis, said the message from the study is a very important one, especially since activities ingrained early in life set the stage for what individuals do in their later and older years. “We’re living in an age right now where it’s so easy to do no physical activity at all,” said Baggish. “We don’t need to walk anywhere, we don’t need to ride our bikes anywhere, and kids can basically go through an entirely normal childhood existence where, unless they’re forced or choose to play sports, they don’t have to do anything. This study shows that the more activity that you do, even if it’s outside the context of typical exercise, really does make a difference.”

In the ICAD analysis, 20,871 children and adolescents from Australia, Brazil, Europe, and the US had the amount of physical activity analyzed from raw accelerometer data. Nearly 75% of the children were considered normal weight, while 17.7% were classified as overweight and 7.4% as obese. Physical-activity levels were monitored for an average of 5.2 days using the accelerometer, and the mean daily time spent engaged in moderate to vigorous physical activity was 30 minutes. The mean daily time spent sedentary was 354 minutes.

Kids in the highest tertile spent more than 35 minutes per day engaged in moderate to vigorous physical activity, whereas those in the bottom tertile were moderately or vigorously active just 18 minutes per day. The mean difference in waist circumference between the most active and least active kids with the most sedentary time was 5.6 cm (95% CI 4.8-6.4 cm) and 3.6 cm (95% CI 2.8-4.3 cm) in those with less sedentary time. Similarly, the difference in systolic blood pressure between the most active and least active kids with the most sedentary time was 0.7 mm Hg (95% CI -0.07 to 1.6 mm Hg), while there was a 2.6-mm-Hg difference (95% CI -1.4 to -3.9 mm Hg) between the most active and least active kids who reported less sedentary time.

The variations in HDL cholesterol, insulin, and triglyceride levels were similar when analyzed by physical-activity levels and sedentary time.

Overall, the results showed that higher levels of physical activity were associated with better cardiometabolic risk factors across the tertiles of sedentary time. In contrast, sedentary time was not associated with any of metabolic outcomes independent of the time engaged in moderate and vigorous activities. The researchers note that they did not qualify what specific activities the children were engaged in while being sedentary. For this reason, reducing television viewing time is still considered an important goal of parents and public-health policy because TV watching is also associated with other unhealthy behaviors, such as snacking and drinking soda.

The American Heart Association adult guidelines do not specifically address pediatric exercise volume, but the analysis by Ekelund and colleagues demonstrates that more is likely better.

Ekelund U, Luan J, Sherar LB, et al. Moderate to vigorous physical activity and sedentary time and cardiometabolic risk factors in children and adolescents. JAMA 2012; 307:704-712.