Outdoor time is associated with physical activity, sedentary time, and cardiorespiratory fitness in youth.

OBJECTIVE: To determine whether time spent outdoors was associated with increased moderate-to-vigorous physical activity (MVPA) and related health benefits in youth. STUDY DESIGN: We performed a cross-sectional study of 306 youth aged 13.6 ± 1.4 years. The exposure of interest was self-reported time spent outdoors after school, stratified into three categories: none, some, and most/all of the time. The main outcome of interest was accelerometer-derived MVPA (Actical: 1500 to >6500 counts/min). Secondary outcomes included sedentary behavior, cardiorespiratory fitness, overweight status, and blood pressure. RESULTS: Among the 306 youth studied, those who reported spending most/all of their after-school time outdoors (n = 120) participated in more MVPA (61.0 ± 24.3 vs 39.9 ± 19.1 min/day; adjusted P < .001), were more likely to achieve the recommended minimum 60 min/day of MVPA (aOR 2.8; 95% CI, 1.3-6.4), spent less time in sedentary activities (539 ± 97 min/day vs 610 ± 146 min/day; adjusted P < .001), and had higher cardiorespiratory fitness (49 ± 5 vs 45 ± 6 mL/kg/min; adjusted P < .001) than youth who reported no time outdoors (n = 52). No differences in overweight/obesity or blood pressure were observed across the groups. CONCLUSIONS: Time spent outdoors is positively associated with MVPA and cardiorespiratory fitness in youth and negatively associated with sedentary behavior. Experimental trials are needed to determine whether strategies designed to increase time spent outdoors exert a positive influence on physical activity and fitness levels in youth.

Anthropometric and dietary predictors of insulin sensitivity in 10- to 14-year-old boys and girls.

The high prevalence of pediatric obesity has made preventing chronic diseases through healthy lifestyle behaviours a priority within pediatrics. Examining the association between diet and insulin sensitivity (IS) in youth may provide important insights for tailoring preventative dietary interventions. The objective of this study was to explore the associations among anthropometry, diet, and IS in 10- to 14-year-olds. In this cross-sectional study, the primary outcome measure was IS, measured noninvasively using a (13)C glucose breath test. Exposure variables included body mass index (BMI) z score and several dietary variables, including glycemic index (GI), glycemic load, and fiber, magnesium, vegetable and fruit, and fat intakes, all of which were derived from a validated, Web-based 24-h recall tool. Multiple regression analyses were performed for boys and girls separately. In total, 378 students (227 girls) aged 12.1 ± 1.2 years were studied. In this sample ∼24% of youth were considered overweight or obese (BMI z score = 0.41 ± 0.93). Multiple regression analyses showed that BMI z score was negatively and independently associated with (13)C insulin sensitivity score ((13)CISS) in both boys and girls (boys: ß = -0.501; girls: ß = -0.446; both p < 0.001). GI was negatively and independently related to (13)CISS in boys (ß = -0.195, p < 0.05) but not in girls. Other dietary variables were not associated with IS. In addition to BMI z score, a low GI diet predicted (13)CISS in boys but not in girls. This finding suggests that interventions that reduce BMI (in both sexes) and include a low GI diet among boys may improve IS.

Physical activity intensity and cardiometabolic risk in youth.

OBJECTIVE: To determine the association between physical activity (PA) intensities and cardiometabolic risk factors in youth. DESIGN: Cross-sectional study using data from the 2008 Healthy Hearts Prospective Cohort Study of Physical Activity and Cardiometabolic Health in Youth. SETTING: Rural and urban communities in Alberta, Canada. PARTICIPANTS: A convenience sample of 605 youth aged 9 to 17 years. Youth were on average aged 12.1 years, 248 were boys (41%), and 157 were overweight or obese (26%). MAIN EXPOSURE: Actical accelerometer-measured PA intensity. MAIN OUTCOMES MEASURES: The primary outcome was body mass index (calculated as weight in kilograms divided by height in meters squared) z score. Secondary outcome measures included waist circumference, systolic blood pressure, and cardiorespiratory fitness (maximal oxygen consumption [[Vdot]O2max]). RESULTS: Body mass index z score, waist circumference, and systolic blood pressure decreased and [Vdot]O2max increased in a dose-response manner across tertiles of vigorous PA (adjusted P < .001). No significant differences in cardiometabolic risk factors were seen across tertiles of moderate or light PA in multivariable analyses. Achieving more than 7 minutes of vigorous PA daily was associated with a reduced adjusted odds ratio of overweight status (0.56; 95% CI, 0.33-0.95) and elevated systolic blood pressure (0.36; 95% CI, 0.16-0.79). The odds of overweight status and elevated blood pressure decreased with increasing time and intensity of PA. CONCLUSIONS: Only vigorous PA was consistently associated with lower levels of waist circumference, body mass index z score, systolic blood pressure, and increased cardiorespiratory fitness in youth. These findings underscore the importance of vigorous PA in guidelines for children and adolescents.

Cardiorespiratory fitness and the risk of overweight in youth: the Healthy Hearts Longitudinal Study of Cardiometabolic Health.

The primary objective of this longitudinal study was to determine the association between cardiorespiratory fitness and the risk of overweight status in youth. To accomplish this aim we analyzed data from annual school-based surveys of cardiorespiratory fitness and anthropometry conducted between 2004 and 2006. The first analysis was performed on a cohort of 902 youth aged 6-15 years followed for 12 months to assess the association between cardiorespiratory fitness levels determined from a graded maximal field test and the risk of becoming overweight. The second analysis was conducted on a cohort of 222 youth followed for 2 years to assess the continuous association between annual changes fitness and weight gain. Children with low cardiorespiratory fitness were characterized by higher waist circumference and disproportionate weight gain over the 12-month follow-up period (P < 0.05). Within the entire cohort, the 12-month risk of overweight classification was 3.5-fold (95% confidence = 2.0-6.0, P < 0.001) higher in youth with low cardiorespiratory fitness, relative to fit peers. A time series mixed effects regression model revealed that reductions in cardiorespiratory fitness were significantly and independently associated with increasing BMI (r = -0.18, P < 0.05) in youth. Accordingly, low cardiorespiratory fitness and reductions in fitness over time are significantly associated with weight gain and the risk of overweight in children 6-15 years old. An assessment of cardiorespiratory fitness using a common field test may prove useful for the identification of youth at risk of overweight and serve as a potential target for obesity prevention.

The relationship between weight gain and blood pressure in children and adolescents.

BACKGROUND: The aim of this study was to determine the relationship between the trajectories of weight gain and systolic blood pressure (SBP) in youth. METHODS: Annual surveys of anthropometry, fitness, SBP, and its determinants (cardiac output, systemic vascular resistance, and arterial compliance) were conducted in youth (aged 5 to 19 years) in a school-based setting between 2004 and 2006. Children were stratified according to change in body mass index (BMI) over time. RESULTS: Within the entire cohort (n = 2089), mean SBP (121 +/- 16 SD v 112 +/- 15 SD mm Hg; P < .01) and the prevalence of high blood pressure (48% v 18%, P < .01) were significantly higher and fitness levels were lower (P < .01) in obese children, relative to healthy-weight peers. After 2 years of follow-up, despite similar SBP and BMI at baseline, the average change in SBP was approximately 4.5-fold greater in children with the largest increase in BMI, relative to children who experienced minimal weight gain. This group also experienced a significantly greater increase in stroke volume (P < .05), while the change in heart rate, arterial compliance, and systemic vascular resistance was comparable with that of children who experienced minimal weight gain. Multiple linear regression analysis revealed that SBP increased 0.77 mm Hg for every kilogram of weight gain over a period of 2 years (P < .01). CONCLUSIONS: Overweight and disproportionate weight gain in children are associated with elevated SBP. These data support the need for interventions to prevent excessive weight gain and obesity in children and adolescents.