Exercise Alone Can't Slim Down Overweight Preschoolers

GLASGOW, Scotland, Oct. 6 -- For overweight or obese preschoolers, an extra dose of physical activity was not enough to shed the pounds, found researchers here.

An additional 90 minutes of exercise a week at school, along with home-based health education to increase active play, had no effect on body mass index (BMI) or exercise habits, reported John J. Reilly, Ph.D., of the University of Glasgow, and colleagues, online today in BMJ.

Diet and other factors will likely need to change along with physical activity to see any lasting benefit for these children, the researchers noted.

"Successful interventions to prevent obesity in early childhood may require changes not just at nursery, school, and home but in the wider environment," they wrote. "Changes in other behaviors, including diet, may also be necessary."

The study was prompted by data showing that at least 10% of Scottish children ages four to five have a BMI at or above the 95% percentile. It included 545 children (mean age 4.2 years) in 36 preschool centers in Glasgow. The centers were paired by type, size and neighborhood socioeconomic status. One center in each pair was randomized to be a control.

The physical activity intervention consisted of three 30-minute sessions of exercise at school for 24 weeks along with an education component for the student's parents to promote physical activity through play and reduce sedentary behavior.

After six months of follow-up, the standard deviation score for BMI was 0.46. By 12 months of follow-up, the standard deviation score was 0.41 for children in the intervention group. However, neither was significantly different from the 0.43 found at both time points for controls (P=0.87 and P=0.90, respectively) though the study was powered at 80% to detect a reduction in score of just 0.125.

Likewise, habitual levels of physical activity measured by accelerometry were unchanged (P=0.18). The percentage of time spent sedentary was also similar at 67.0% for the intervention group and 62.9% for controls (P = 0.08).

Surprisingly, the time spent in moderate or vigorous physical activity was "marginally" better for the control group (3.5% intervention group versus 4.1% control group, log percentage time P=0.05).

However, there were some potentially important changes in fundamental movement skills. Children in the intervention group improved their motor skills by 0.8 units on a scale of 0 to 15 compared with the control group. Girls responded significantly more than boys, with an average difference in improvement between genders of 0.7 units (0.3 improvement for boys versus 1.1 for girls, P=0.001).

The investigators suggested that this may "foster an increase in activity levels in future by increasing confidence or ability, or both, in children to carry out physical activity and may have direct effects on body fat content in the long term."

While previous studies have found some benefit to physical activity interventions at school, most of the trials have been small or poorly controlled.

The extra activity in the study here fell short of providing the daily minimum of 30 minutes of moderate-to-vigorous physical activity at school recommended in August by the American Heart Association.

The study was funded by the British Heart Foundation, the Glasgow City Council, and the Caledonian Research Foundation.