Exercise Dose and Diabetes Risk in Overweight and Obese Children: A Randomized Controlled Trial
Do different amounts (i.e., doses) of aerobic exercise influence insulin resistance, fatness, visceral fat, and fitness among overweight sedentary children?
This was a randomized controlled efficacy trial, which enrolled overweight and obese sedentary children recruited from 15 public schools between 2003 and 2007. All children attended schools in the Augusta, Georgia area. The intervention consisted of aerobic exercise at low dose (20 minutes/day) or high dose (40 minutes/day) for 5 days per week, with a third control group randomized to usual physical activity. Mean duration of follow-up was 13 weeks (standard deviation [SD] 1.6 weeks). The primary outcomes of interest included post-intervention type 2 diabetes risk assessment through insulin area under the curve (AUC) (from an oral glucose tolerance test), aerobic fitness (peak oxygen consumption [VO2]), percent body fat (via dual-energy x-ray absorptiometry), and visceral fat (via magnetic resonance). Analyses were performed as intention-to-treat.
A total of 222 children (mean age 9.4 years) were enrolled in the trial, of which 42% were male and 58% were black. The majority of participants (85%) were obese. Mean body mass index of the study population was 26 (SD 4.4) at baseline. Study retention was excellent (n = 209, 94%). Reductions in insulin AUC were larger in the high-dose group (adjusted mean difference, −3.56 [95% confidence interval (CI), −6.26 to −0.85] x 103 μU/ml; p = 0.01) and the low-dose group (adjusted mean difference, −2.96 [95% CI, −5.69 to −0.22] x 103 μU/ml; p = 0.03) compared to the control group. Dose response trends were also observed for body fat (adjusted mean difference, −1.4% [95% CI, −2.2% to −0.7%]; p < 0.001 and −0.8% [95% CI, −1.6% to −0.07%]; p = 0.03) and visceral fat (adjusted mean difference, −3.9 cm3 [95% CI, −6.0 to −1.7 cm3]; p < 0.001 and −2.8 cm3 [95% CI, −4.9 to −0.6 cm3]; p = 0.01) in the high- and low-dose groups versus the control group, respectively. Effects in the high- and low-dose groups versus control group were similar for fitness (adjusted mean difference in peak VO2, 2.4 [95% CI, 0.4-4.5] ml/kg/min; p = 0.02 and 2.4 [95% CI, 0.3-4.5] ml/kg/min; p = 0.03, respectively). No effect modification was observed for sex or race.
The investigators concluded that a 13-week trial of 20 minutes/day or 40 minutes/day of aerobic training can improve fitness and insulin resistance while reducing fatness including visceral adiposity among sedentary overweight and obese children, irrespective of sex or race.
This is a well-designed study, which demonstrates significant improvements in diabetes risk factors associated with daily exercise, even of limited duration such as 20 minutes per day. As the authors point out, the 5 days per week may be a critical contributor to the health benefits of exercise observed in this trial. Finding time in the school day or after school for physical activity could translate into significant improvements in diabetes-related risk factors among overweight or obese children.
Keywords: Child, Insulin, Absorptiometry, Photon, Body Mass Index, Glucose Tolerance Test, Exercise, Obesity, Georgia, Diabetes Mellitus
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