The basic idea is conventional wisdom: Children who spend more time physically active than their sedentary peers will generally be healthier. Now a new study in the current Journal of the American Medical Association has refined this common understanding, looking specifically at the amount of time spent physically active and sedentary as it relates to certain risk factors in otherwise healthy children. The findings suggest that the length of time a child spends being physically active, regardless of sedentary time, is key to improved heart and metabolic health.
For the purposes of their study, researchers led by an epidemiologist at the Institute of Metabolic Science in the UK analyzed data from 14 studies between 1998 and 2009, comprising nearly 21,000 children aged 4 to 18 years. The researchers looked specifically at the amount of time the kids spent engaged in moderate- to vigorous-intensity physical activity (MVPA), which was measured using accelerometers (devices that measure activity and the level or intensity of activity). They then looked at children’s MVPA in the context of their sedentary time and measures of cardiometabolic status, which included waist circumference, systolic blood pressure, insulin, fasting triglycerides, and HDL cholesterol.
Not surprisingly, the children who spent 35 minutes or more a day in MVPA had better cardiometabolic measurements than those who spent less than 18 minutes a day at that level of physical activity. Somewhat surprisingly, however, the greater amount of MVPA time was associated with better parameters, regardless of the amount of time spent sedentary.
“So the amount of sedentary time is not the key variable,” ACSH's Dr. Gilbert Ross observes. “According to this study, it’s the amount of physical activity that really matters.” He acknowledges that this is an area where little data exists, but he believes this metanalysis makes a useful point: Regular physical activity is indeed integral to good health.
“Thus the concern about children spending too much time in sedentary activity is perhaps excessive,” says ACSH’s Dr. Ruth Kava. “There just has to be a counterbalancing amount of moderate or vigorous physical activity.”
