Thursday, December 13, 2007

Can Physical Activity Avert Obesity in School-Aged Youth?

The CDC convened a panel of experts to evaluate the evidence for the beneficial effects of physical activity on a broad range of health outcomes and behaviors, including body fat content (adiposity) in school-aged youth, ages 6 to 18. The experts based their evaluation on more than 850 relevant scientific studies. Here we discuss only those findings related to overweight or obesity.

The panelists noted that comparing the findings among studies was somewhat difficult since the definitions of overweight and obesity in youth have varied over time and different studies focused on different indicators of adiposity. But there was agreement that both cross-sectional studies (studies of children of similar age at only one point in time) and longitudinal studies (studies in which a group of children are measured more than once over a period of time, usually months or years) provide evidence that youth of both sexes who are highly active are less fat than their less active counterparts. More specifically:

* In overweight children and teens, moderate intensity exercise that lasts 30 to 60 minutes three to seven days a week leads to a reduction in total body fat and visceral fat. (Visceral fat is located in the abdominal area and is generally regarded as more dangerous to health than total body fat).
* For normal weight boys and girls, more intensive and longer sessions of physical activity (greater than 80 minutes a day) are needed to reduce the body fat percentage or proportion of body weight that is fat weight.
* Although data on injury are scant, physical education and after-school programs designed to increase physical activity in children and youth are associated with an injury rate that is extremely low or nearly zero.
* There are many beneficial effects of physical activity including favorable effects on cardiovascular health, asthma, mental health, academic performance, memory, behavior, bone mineral and muscular strength and endurance.

The report, however, did not specify the level of physical activity that is clearly associated with maintaining normal adiposity, or body fatness, over time. Since adiposity varies greatly in school-aged youth and the patterns of fat accumulation differ in males and females as they grow and develop, "normal" means a level of adiposity that is appropriate for the child's age and gender. The report suggests that higher levels of moderate to vigorous physical activity, meaning 30 to 80 minutes a day three to seven days a week, may be needed to prevent obesity in youth. Vigorous activity is defined as activity performed at a level of intensity that causes sweating and breathing hard. A wide variety of aerobic activities are suitable, so the challenge for youth, as it is for adults, is to find activities that are enjoyable.

References for "Can Physical Activity Avert Obesity in School-Aged Youth?"