Successful overweight prevention in adolescents by increasing physical activity: a 4-year randomized controlled intervention.

BACKGROUND: Population-based studies directed at promoting physical activity in youth have shown limited success in obesity prevention. OBJECTIVE: To assess whether an intervention integrating environmental changes to induce sustained changes in physical activity, prevents overweight in adolescents. DESIGN: Four-year randomized trial started in 2002 in eight middle schools of Eastern France. The intervention, randomized at school level, was designed to promote physical activity by changing attitudes through debates and attractive activities, and by providing social support and environmental changes encouraging physical activity. SUBJECTS: Nine hundred and fifty four 12-year-old six-graders. MEASUREMENTS: Body mass index (BMI), body composition, physical activity by questionnaire, plasma lipids and glucose, insulin resistance. RESULTS: Intervention students had a lower increase in BMI (P=0.01) and age- and gender-adjusted BMI (P<0.02) over time than controls. The differences across groups of the age- and gender-adjusted BMI changes (95% confidence interval (CI)) were -0.29 (-0.51; -0.07) kg/m2 at 3 years, -0.25 (-0.51; 0.01) kg/m2 at 4 years. An interaction with baseline weight status was noted. The intervention had a significant effect throughout the study in initially non-overweight adolescents (-0.36 (-0.60;-0.11) kg/m2 for adjusted BMI at 4 years), corresponding to a lower increase in fat mass index (P<0.001). In initially overweight adolescents, the differences observed across groups at 2 years (-0.40 (-0.94; 0.13) kg/m2 for adjusted BMI) did not persist over time. At 4 years, 4.2% of the initially non-overweight adolescents were overweight in the intervention schools, 9.8% in the controls (odds ratio=0.41 (0.22; 0.75); P<0.01). Independent of initial weight status, compared with controls, intervention adolescents had an increase in supervised physical activity (P<0.0001), a decrease of TV/video viewing (P<0.01) and an increase of high-density cholesterol concentrations (P<0.0001). CONCLUSION: Enhancing physical activity with a multilevel program prevents excessive weight gain in non-overweight adolescents. Our study provides evidence that prevention of obesity in youth is feasible.

Adiponectin is associated with lipid profile and insulin sensitivity in French adolescents.

AIM: The favourable relationship of adiponectin with the metabolic profile demonstrated in adults has been less studied in youths. The aim of this study was to examine cross-sectional and longitudinal associations between adiponectin and various metabolic risk factors in 12-year-old adolescents. METHODS: Subjects were participants in a randomized controlled study to promote physical activity (PA). Cross-sectional associations were assessed at entry in 2002 among 647 PA-exposed and control first-level students (49% male, 11.6+/-0.6 years of age). Longitudinal analyses involved 288 control students surveyed in 2002 and 2004. Baseline measurements included fasting serum adiponectin and anthropometric indices (body mass, waist size, body fat [BF] by bioimpedance), insulin concentration, homeostasis model assessment (HOMA), high-density lipoprotein (HDL) cholesterol, triglycerides (TG), soluble TNF-alpha receptor 1 (sTNF-alpha R1) and high-sensitivity C-reactive protein. Analyses were performed with generalized linear mixed-effects models, taking into account correlations among adolescents in the same school. RESULTS: Cross-sectionally, plasma adiponectin was inversely associated with obesity indices, especially waist size (P<10(-2)), HOMA (P<0.03), insulin (P<0.04), TG (P<10(-2)) and sTNF-alpha R1 (P<0.05), and positively related to HDL cholesterol (P<10(-4)), after adjusting for age, gender, sexual maturity, sports participation and adiposity when relevant. Longitudinally, a higher baseline adiponectin level was associated with a more favourable two-year change in TG (P<0.05), even after accounting for baseline TG, and two-year BF and insulin changes. CONCLUSION: The findings of this study suggest a favourable relationship between adiponectin and both metabolic profile and subsequent changes in TG level in young adolescents.

Habitual physical activity, physical fitness and heart rate variability in preadolescents.

The amount and type of physical activity (PA) appropriate in youth for optimal health is still being discussed. The purpose of this study on 12-year-old preadolescents is to evaluate the association of two PA patterns, corresponding to different exercise intensities, with some health-related indexes. PA was evaluated by triaxial accelerometry in 67 student subjects, who were successively classified according to 1) their usual participation or not in moderately intense (> 4 metabolic equivalents, METs) activities (either in daily life or in leisure activities) for at least 210 min a week (4 M (210)); and 2) the habitual practice or not of more intense activities (> 6 METs) for at least 60 min a week (6 M (60)). Health-related indexes consisted of cardiopulmonary (maximum oxygen uptake, V.O 2max), muscular (lower limb strength) fitness parameters and vagal-related indexes of heart rate (HR) variability (HRV), such as the HF/(LF+HF) ratio (where HF and LF stand for high and low frequency power). HR was recorded in the supine position after 15 min of quiet rest, and HRV indexes were calculated in 5-min segments. Energy expenditure due to PA was not significantly associated with any health-related index. Reaching 4 M (210) was associated with both higher estimated V.O 2max (p < 0.05) and higher muscular strength indexes (p < 0.05) but not with enhanced HRV indexes. Subjects who reached 6 M (60) had higher estimated V.O2max (p < 0.05) and higher HF/(LF+HF) (p < 0.05). Our results show that regular moderately intense activities are sufficient to influence physical fitness but suggest that more intense activities are necessary to observe more favorable HRV vagal-related indexes.

Physical activity is inversely related to waist circumference in 12-y-old French adolescents.

BACKGROUND AND OBJECTIVE: Waist circumference (W) has been shown to be a good predictor of cardiovascular risk. The aim of this study was to investigate whether physical activity (PA) is related to W in adolescents as previously shown in adults. DESIGN AND SUBJECTS: Cross-sectional population-based survey of 2,714 12-y-old adolescents from the eastern part of France. MEASUREMENTS: Body mass index (BMI) and W were measured. Structured PA, active commuting to and from school and sedentary activities (SED), for example television viewing, computer/video games and reading and different potential confounders (dietary habits, parental overweight, family annual income tax and educational level) were assessed by a questionnaire. RESULTS: The adolescents had a mean BMI of 19.0+/-3.4 kg/m2, and 20.2% of them were overweight, with no gender difference. Boys had a greater W than girls (67.6+/-9.1 vs 65.7+/-8.9 cm, P<0.0001). In all, 42% of the girls and 25% of the boys did not practice any structured PA outside school and less than 40% of the adolescents commuted actively to school more than 20 min/day. About one-third of the adolescents devoted more than 2 h/day to SED. In univariate analyses, BMI was negatively associated with structured PA but significantly only for girls (P<0.01) and positively associated with SED for both genders (P<0.0001 for girls, P<0.01 for boys). W was negatively associated with structured PA and positively associated with SED both in girls (P<0.0001 and P=0.03, respectively) and boys (P<0.01 and P=0.08, respectively). Multiple general linear models show that SED is associated with BMI, independently of structured PA, in both genders. On the other hand, structured PA was inversely associated with W, independently of SED. The inverse relation between structured PA and W persisted after additional adjustment on BMI, with a greater effect of PA for the adolescents with higher BMI. CONCLUSIONS: In 12-y-old adolescents, structured PA is inversely associated with W, an indicator of total adiposity but also more specifically of abdominal fat. This suggests that PA may have a beneficial effect on youth metabolic and cardiovascular risks, in particular in the presence of overweight..