Childhood obesity has become one of the most widespread public health problems in the United States, and it has received tremendous media attention in recent years. Obesity in children and adolescents has been thought to be a significant risk factor for cardiac disease, diabetes, and high blood pressure later in life.

Physical activity is felt to be one of the best means of combating childhood obesity. In addition to being associated with a lower risk of cardiovascular issues, physical activity is believed to be associated with better mental health and social skills. It is recommended that children and adolescents perform at least 60 minutes of moderate-to-vigorous physical activity per day.

Does much of the childhood population engage in that level of physical activity, and does that activity level increase or decrease over time? Laura Basterfield et al. published a study in the January 2011 edition of Pediatrics that shines light on these questions.

The authors had children aged 6 to 8 wear accelerometers on their hips during waking hours for 7 days to measure physical activity and energy expenditure. Two years later, these children’s activity was again tested.

Not surprisingly, physical activity levels were low. The children averaged 26 minutes per day of moderate-to-vigorous physical activity at an average of 7 years old and 24 minutes per day at an average of 9 years old. Only 6.4% of children averaged the recommended 60 minutes per day of moderate-to-vigorous physical activity at age 7 and 5.7% did age 9. Only 2.2% of children performed 60 minutes per day at both measurement periods.

The authors concluded that the low levels of activity and high levels of sedentary activity are established early in life and only get worse later in childhood. Basterfield states, “Our results suggest that public health interventions aimed at preventing declines in physical activity should be targeting elementary school-aged children, because unfavorable trends in health behaviors seem to be already established before puberty.”

Vitamin D deficiency might be a risk factor

Another factor that seems to be associated with childhood obesity is vitamin D deficiency. Diane Gilbert-Diamond et al. presented their findings in an article in the December 2010 edition of the American Journal of Clinical Nutrition. They studied 3202 children aged 5 to 12 and measured vitamin D levels, body mass index (BMI), and two locations of skinfold thickness to determine truncal and central obesity. The authors found that lower vitamin D levels were associated with higher BMI and measures of central adiposity.

A proposed solution

As gloomy as this data seems, there might be a fairly simple solution – or at least a place to start. Russell Jago et al. published a study in the February 2011 edition of Medicine & Science In Sports & Exerciselooking at the influence of best friends on a child’s physical activity level. The authors studied 472 children aged 10 to 11. They used accelerometers to measure the children’s activity. They also used questionnaires to identify their children’s best friends, how often they play together, how often it involved physical activity, and where the activity typically occurred.

The authors determined that the physical activity levels of 10- to 11-year-old children were closely related to physical activity levels of their best friends. In addition, being active with their friends at home or in their neighborhoods led to increased physical activity compared to physical activity only at school.

Therefore, it seems to me the benefits of children playing with friends might decrease obesity in two ways. First, we know that direct exposure to sunlight is one of the primary means of acquiring vitamin D (in addition to the diet). If vitamin D deficiency is associated with childhood obesity, as the Gilbert-Diamond study suggests, then playing outside on sunny days might lead to increased vitamin D levels and lower BMI’s. Also, physical playtime with friends who are active, not just at school but outside of school, might help kids get the recommended 60 minutes of moderate-to-vigorous physical activity per day.