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The effect of screen time during secondary school on percent body fat was examined in a cohort of 744 Canadian adolescents aged 12–13 years at baseline. Participants completed self-reported questionnaires on television viewing and computer use in 19 survey cycles over 57 months from 1999 to 2005. Triceps skinfold thickness and subscapular skinfold thickness were measured in survey cycles 1 and 19. Four screen-time trajectory groups identified in growth mixture modeling included steady-low screen time (73% of the sample), steady-high (10%), increasers (9%), and decreasers (8%). The effect of screen-time trajectory on percent body fat at survey cycle 19 was modeled in boys and girls separately by using linear regression, adjusting for baseline percent body fat and physical activity. Relative to that of steady-low screen-time trajectory group boys, percent body fat was 2.9 (95% confidence interval: 0.7, 5.0) and 2.4 (95% confidence interval: 0.5, 4.2) percentage units higher on average among “increasers” and “steady-high” trajectory group boys, respectively. There was no evidence that screen time has an effect on percent body fat in girls overall, although physical activity modified the association between screen time and percent body fat in both sexes. Efforts to prevent obesity in youth should emphasize reducing screen time. [ABSTRACT FROM PUBLISHER]

The authors examined the potential association between changes in the number of moderate-to-vigorous physical activity (MVPA) sessions per week, adiposity, and systolic blood pressure (SBP) during adolescence. SBP and anthropometric factors were assessed biannually (1999/2000, 2002, and 2004) in a cohort of 1,293 Canadian adolescents aged 12–13 years in 1999. Self-reported 7-day recall data on MVPA sessions ≥5 minutes in duration were collected every 3 months over the 5-year period. Estimates of initial level and rate of decline in number of MVPA sessions per week from individual growth models were used as predictors of SBP in linear regression models. A decline of 1 MVPA session per week with each year of age was associated with 0.29-mm Hg and 0.19-mm Hg higher SBPs in girls and boys, respectively, in early adolescence (ages 12.8–15.1 years) and 0.40-mm Hg and 0.18-mm Hg higher SBPs, respectively, in late adolescence (ages 15.2–17.0 years). The associations were not attenuated by changes in body mass index, waist circumference, or skinfold thickness in girls during late adolescence. Although weaker, associations were evident in boys during late adolescence, as well as in both girls and boys during early adolescence. These results support prevention of declines in MVPA during adolescence to prevent higher blood pressure in youth. [ABSTRACT FROM PUBLISHER]

Background: The natural course of onset of cigarette use has been conceptualized as progressing sequentially through 5 stages (preparation, trying, irregular use, regular use, nicotine-dependent smoking). However, recent studies suggest that symptoms of nicotine dependence can occur early in the onset process, raising questions about the validity of this model. The objective of our study was to describe the sequence and timing of 12 milestones (6 related to cigarette use and 6 to symptoms of nicotine dependence) during onset of cigarette use. Methods: Grade 7 students in 10 secondary schools in Montréal (n= 1293) were followed prospectively every 3-4 months for 5 years. Using Kaplan--Meier analysis, we computed the number of months after first puff at which the cumulative probability of attaining each milestone was 25%, among 311 participants who initiated cigarette use during follow-up. Results: Inhalation rapidly followed first puff. The cumulative probability of inhalation was 25% at 1.5 months (95% confidence interval [CI] 1.5-2.5). The cumulative probability (and 95% CI) was 2.5 months (1.5-2.5) for mental addiction, 2.5 (1.0-3.0) for smoking a whole cigarette, 4.5 (2.5-8.8) for cravings, 5.4 (3.8-9.7) for physical addiction, 8.8 (7.0-11.9) for monthly smoking, 11.0 (6.4-16.8) for withdrawal symptoms, 13.0 (10.3-20.5) for tolerance, 19.4 (14.5-31.7) for weekly smoking, 19.5 (14.0-23.9) for lifetime total of 100 cigarettes, 23.1 (19.7-37.6) for daily smoking and 40.6 (35.1-56.0) for conversion to tobacco dependence. Interpretation: Symptoms of nicotine dependence develop soon after first puff and can precede monthly, weekly and daily smoking. Cessation interventions that manage dependence symptoms may be needed soon after first puff. [ABSTRACT FROM AUTHOR]

Background: Adolescent physical activity (PA) levels track into adulthood. However it is not known if type of PA participated in during adolescence is associated with PA levels later in life. We aimed to identify natural groupings of types of PA and to assess whether number of years participating in these different groupings during adolescence is related to PA level in early adulthood. Methods: 673 adolescents in Montreal, Canada, age 12-13 years at baseline (54 % female), reported participation in 29 physical activities every 3 months over 5 years (1999-2005). They also reported their PA level at age 24 years (2011-12). PA groupings among the 29 physical activities were identified using factor analysis. The association between number of years participating in each grouping during adolescence and PA level at age 24 was estimated using linear regression within a general estimating equation framework. Results: Three PA groupings were identified: "sports", "fitness and dance", and "running". There was a positive linear relationship between number of years participating in sports and running in adolescence and PA level at age 24 years (β (95 % confidence interval) = 0.09 (0.04-0.15); 0.08 (0.01-0.15), respectively). There was no relationship between fitness and dance in adolescence and PA level at age 24. Conclusions: The association between PA participation in adolescence and PA levels in young adulthood may be specific to certain PA types and to consistency of participation during adolescence. Results suggest that efforts to establish the habit of participation in sports and running in adolescence may promote higher PA levels in adulthood. [ABSTRACT FROM AUTHOR]

Background: Efforts to increase physical activity in youth need to consider which activities are most likely to be sustained over time in order to promote lifelong participation in physical activity. The Monitoring Activities of Teenagers to Comprehend their Habits (MATCH) study is a prospective cohort study that uses quantitative and qualitative methods to develop new knowledge on the sustainability of specific physical activities. Methods/design: Eight hundred and forty-three grade 5 and 6 students recruited from 17 elementary schools in New Brunswick, Canada, are followed-up three times per year. At each survey cycle, participants complete self-report questionnaires in their classroom under the supervision of trained data collectors. A sub-sample of 24 physically active students is interviewed annually using a semi-structured interview protocol. Parents (or guardians) complete telephone administered questionnaires every two years, and a health and wellness school audit is completed for each school. Discussion: MATCH will provide a description of the patterns of participation in specific physical activities in youth, and enable identification of the determinants of maintenance, decline, and uptake of participation in each activity. these data will inform the development of interventions that take into account which activities are the most likely to be maintained and why activities are maintained or dropped. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The objective of this study is to examine depressive symptom trajectories during adolescence as predictors of physical activity (PA) in young adulthood. Methods: Adolescents residing in Montreal, Canada (n=860) reported their depressive symptoms every 3–4months during high school in 20 data collections. Three years later, participants reported engaging in moderate and vigorous intensity PA and team sports participation. Trajectories of depressive symptoms were estimated using latent growth modeling and examined as predictors of PA outcomes. Results: Three depression symptom trajectory groups were identified during adolescence: low and declining depressive symptom scores (group 1; 37.8%); moderate and stable depressive symptom scores (group 2; 41.6%); and high increasing depressive symptom scores (group 3; 20.6%). In multivariable analyses, group 2 and group 3 participated in less moderate-intensity PA and were less likely to participate in team sports compared to group 1. Conclusions: The importance of examining intensity and type of PA as outcomes of depressive symptoms is highlighted. Targeted approaches are needed to encourage adolescents with moderate to high depression symptoms to engage in PA and team sports to improve their health and well-being. [Copyright &y& Elsevier]

Purpose. The association between physical activity (PA) and inflammation has been established in adults, yet little is known about this relationship in youth. This study examined the relationship between vigorous PA and C-reactive protein (CRP) in adolescents. Methods. Data were available for 1 520 adolescents, aged 13 and 16 years, in a province-wide survey of a representative sample of youth in Québec, Canada. Participants completed questionnaires assessing VPA, pubertal stage, body image, and health problems; they provided a fasting blood sample for CRP; and they had height and weight measured. Results. In sex-specific multivariable logistic regression models, VPA was protective of elevated CRP in boys (OR=0.60, 95%CI=0.37-0.99) independent of weight status, pubertal stage, anti-inflammatory/antibiotic medication, and smoking. CRP and physical activity were not related in girls (OR=1.12, 95%CI=0.69-1.82). Conclusions. In addition to many known health benefits of VPA, the current findings provide evidence that VPA may protect against low-grade systemic inflammation in boys. These data provide further support for the importance of promoting healthy PA levels in youth. [ABSTRACT FROM AUTHOR]