International physical activity guidelines for young people need to be changed

International guidelines need to recommend higher levels of physical activity for young people than they currently do, in order to lower their risk of cardiovascular disease, according to a study in this week's issue of The Lancet.

Currently, guidelines recommend that young people should participate in physical activity of at least moderate intensity for 1 hour per day. However, the evidence for this advice comes from studies that may have been biased because they relied on children recalling the amount of exercise they do. These studies have also only looked at single risk factors for cardiovascular disease.

In the latest research, Lars Bo Andersen (Norwegian School of Sports Science, Oslo, Norway) and colleagues randomly selected over 1730 children, aged 9 or 15 years, from schools in Denmark, Estonia, and Portugal to take part. They measured a combination of risk factors for cardiovascular disease in the children including blood pressure, weight, waist circumference, insulin resistance, and cholesterol and calculated a combined risk factor score for each child. Physical activity was monitored for four consecutive days using a device called an accelerometer, which was strapped to childrens' hips, to measure acceleration of body movement. The researchers found that the combined risk factor score for cardiovascular disease decreased with increasing physical activity. The lowest risk factor scores were found in the 9 year olds who did 116 minutes of moderate to vigorous intensity activity (corresponds to a walking speed of around 4 km/h) and the 15 year olds who did around 88 minutes daily. The research suggests that guidelines should recommend one and a half hours or more of moderate intensity exercise per day for young people instead of one hour.

Professor Andersen concludes: "…the current guidelines of at least 1h per day of physical activity of at least moderate intensity could be an underestimation of the activity necessary to prevent clustering of risk factors in younger children."