Wonwoo Byun

Sedentary behaviour in youth

The purpose of this review is to describe the amount of time children spend in sedentary behaviour and to determine if there are specific factors that associate with sedentary behaviour in children. The following search terms were used to identify relevant articles: sedentary behaviour, inactivity, television, computer, video games, small screen, sitting, prevalence, patterns, correlates, factors and determinants. The databases used to conduct the search included PubMed, PsycINFO, ERIC (Education Resources Information Center) and Academic Search Premier. The studies reviewed were limited to those that sampled children (2–18 years), were written in English and used a measure of sedentary behaviour as the dependent variable. Several studies reported the time spent watching television or the proportion of children at or above a threshold for television viewing (eg, ≥3 h/day). Among the accelerometer studies included, the National Health and Nutrition Examination Survey is the largest and reported ∼6.1, 7.5 and 8.0 h/day mean sedentary time in children 6–11, 12–15 and 16–19 years old, respectively. Taken together, the existing literature across the world indicates a slightly higher level of sedentary behaviour in older children. Higher levels of sedentary behaviour were also reported in non-white children, children from lower socioeconomic status background and children from households with more access to televisions/computers. Lower levels of sedentary behaviour were reported in children whose parents have rules/limitations on screen time.

Accelerometer-derived physical activity levels of preschoolers: a meta-analysis.

OBJECTIVES This study synthesized the published estimates of daily moderate-to-vigorous physical activity (MVPAd(-1)) of preschooler-age children (3-5 years). DESIGN Meta-analysis of previously published studies reporting accelerometer-derived estimates of daily MVPA of preschoolers. METHODS A comprehensive literature review was conducted to identify studies published by March 2010 that reported daily minutes of accelerometer-derived MVPA in preschool-age children (3-5 years). Random effects point estimates and 95% confidence intervals (95% CIs) were calculated based on study weighted means and standard deviations of raw accelerometer counts per minute (cpm) and reported minutes of MVPA and/or percentage of time spent in MVPAd(-1). RESULTS 29 articles representing 6309 preschoolers were included. Overall, preschoolers engaged in 42.8 min (95% CI 28.9-56.8) of MVPAd(-1), and 54.4 min (95% CI 29.9-78.9) and 45.4 min (95% CI 25.2-65.6) for boys and girls separately. This translated into approximately 5.5% (95% CI 3.7-7.2%) of time spent in MVPAd(-1), and 7.1% (95% CI 3.9-10.3%) for boys and 6.3% (95% CI 3.9-8.7%) for girls. Studies (76%) using ActiGraph accelerometers reported an average of 714 cpm (95% CI 678-751), with boys and girls having 783 cpm (95% CI 753-813) and 696 cpm (95% CI 665-727), respectively. CONCLUSIONS Interpretation of accelerometer-derived MVPA is confounded by differences in cutpoints applied within a study. Great care, therefore, should be taken when interpreting the activity levels of preschoolers to inform policy decisions, such as the development of physical activity guidelines. Hence, considerable attention is required to unify accelerometer-derived MVPA so that unbiased comparisons across studies can be made.

Parental and Environmental Correlates of Physical Activity of Children Attending Preschool

OBJECTIVE To determine, using a social-cognitive framework and structural equation modeling, if parent-reported family physical activity (PA) variables are related to PA of young children. DESIGN Cross-sectional study. SETTING Children attending 23 preschools in and around Columbia, South Carolina. PARTICIPANTS Three hundred sixty-nine children (48.0% male and 50.4% black) and their parents. MAIN EXPOSURES Family variables were reported by parents and included parent PA, parent enjoyment of PA, importance to adults of child playing sports and being active, and family support. MAIN OUTCOME MEASURES Moderate to vigorous physical activity (MVPA) of children was modeled as a latent variable using PA from direct observation, accelerometers, and parents perception of the childs athletic coordination. RESULTS A model of direct and indirect relations of family variables, preschool quality, home PA equipment, and childs enjoyment of PA had acceptable fit (root mean square error of approximation, 0.053; comparative fit index, 0.90). Parent PA, parent enjoyment of PA, and importance of childs PA were significantly related to family support. Family support, quality of preschool attended, home PA equipment, and childs enjoyment of PA were positively related to childs PA. However, there was no direct relationship between parent PA and the childs PA. CONCLUSION Although parent PA was not directly related to childrens MVPA, results showed that parent PA indirectly affects preschool childrens MVPA via its influence on family support for childrens PA.

Correlates of Objectively Measured Sedentary Behavior in US Preschool Children

OBJECTIVE: To identify correlates of objectively measured sedentary behavior in a diverse sample of preschool children. METHODS: A total of 331 children (51% male, 51% black) from a wide range of ethnic and socioeconomic backgrounds in greater Columbia, South Carolina, were recruited for this study. Sedentary behavior (minutes/hour) was measured by using ActiGraph accelerometers (<37.5 counts per 15 seconds) over a 2-week period. All potential correlates except for anthropometric data of children were measured by a parent survey. Correlation and regression analyses were conducted to examine associations between 29 potential correlates across multiple domains (demographic, biological, psychosocial, behavioral, and physical environmental) and sedentary behavior measured by accelerometry in preschool children. RESULTS: Girls spent more time in sedentary behavior than boys (33.2 vs 32.4 minutes/hour; P = .05). Six and 8 potential correlates were found to be significant in univariate analyses for boys and girls, respectively. In the gender-specific final model, for boys, a childs weekday TV/video games and physical activity equipment in the home were significant correlates of sedentary behavior (R2 = 0.091). For girls, BMI z score and childs athletic coordination were significantly associated with sedentary behavior (R2 = 0.069). CONCLUSION: Several factors were identified as correlates of objectively measured sedentary behavior in American preschool children. However, there were no common correlates that influenced sedentary behavior for both boys and girls. Future interventions for reducing sedentary behavior could target correlates identified in this study.

Associations Between Screen-Based Sedentary Behavior and Cardiovascular Disease Risk Factors in Korean Youth

The purposes of this study were to: 1) describe the patterns of screen-based sedentary behaviors, and 2) examine the association between screen-based sedentary behavior and cardiovascular disease (CVD) risk factors in representative Korean children and adolescents, aged 12 to 18 yr, in the Korean National Health and Nutrition Examination Survey. Screen-based sedentary behavior was measured using self-report questionnaires that included items for time spent watching TV and playing PC/video games. Physical activity was measured using items for frequency and duration of moderate-to-vigorous physical activity (MVPA). CVD risk factors such as body mass index (BMI), waist circumference, LDL cholesterol, HDL cholesterol, total cholesterol, triglycerides, glucose, systolic blood pressure, and diastolic blood pressure were measured. Boys spent more time playing PC/video games, and girls spent more time watching TV. After adjusting for age, gender, annual household income, and MVPA, an additional hour of watching TV was significantly associated with the risk of overweight (OR 1.17 [95% CI 1.03-1.33]), high abdominal adiposity (OR 1.27 [1.06-1.51]), and low HDL cholesterol (OR 1.27 [1.10-1.47]). An additional hour spent playing PC/video games also increased the risk of high abdominal adiposity (OR 1.20 [1.03-1.40]). Prospective observations and interventions are needed to determine causal relationships between screen-based sedentary behavior and CVD risk profiles in Korean youth.

Effect of Positive Health Factors and All-Cause Mortality in Men

PURPOSE Although several health-related factors are independently associated with diverse health outcomes, their combined affect on mortality has not been fully described. METHODS We examined the combined effect of several positive health factors, including having normal weight (body mass index = 18.5-24.9 kg.m), not smoking (not current smoker), consuming a moderate alcohol intake (1-14 drinks per week), being physically active (moderate to high level), and having a higher cardiorespiratory fitness (top two-thirds), on all-cause mortality in 38,110 men aged 20-84 yr from the Aerobics Center Longitudinal Study. RESULTS There were 2642 deaths during an average of 16 yr of follow-up. Compared with men with zero positive health factors, the multivariable-adjusted hazard ratios (HR) of all-cause mortality with one, two, three, four, and five positive health factors were 0.78 (95% confidence interval (CI) = 0.64-0.95), 0.61 (95% CI = 0.50-0.73), 0.54 (95% CI = 0.44-0.65), 0.43 (95% CI = 0.35-0.52), and 0.39 (95% CI = 0.31-0.48), respectively (P for trend <0.001). The combination of five positive health factors accounted for 29% (95% CI = 14%-40%) of population-attributable risk for all-cause mortality. CONCLUSIONS Our findings suggest that targeting more of these modifiable health factors may provide substantial health benefits in middle-aged men.

Sedentary Behavior and Health Outcomes in Children and Adolescents

The purpose of this review was to summarize findings from epidemiological studies that determined if sedentary behavior was associated with obesity, metabolic risk factors, and cardiorespiratory fitness in children and adolescents. We noted if studies adjusted for moderate-to-vigorous physical activity (MVPA), dietary intakes, and/or sleep duration. Articles were identified through PubMed using the search terms: (sedentary OR sitting OR television) AND (adiposity OR blood pressure OR body mass index OR cardiometabolic OR metabolic risk OR waist circumference). The search was limited to ages 6 to 18 years, humans, and published between January 1, 2008 and September 26, 2012. Cross-sectional and longitudinal studies observed associations between more sedentary behavior, especially screen-based sedentary behavior, and measures of obesity; and most associations were independent of MVPA and dietary intake. Cross-sectional and longitudinal studies reported associations between screen-based sedentary behavior and lower cardiorespiratory fitness, and most associations were independent of MVPA and obesity. Cross-sectional studies observed associations between more screen-based and objectively measured sedentary behavior and lower insulin sensitivity; and most associations were independent of MVPA and obesity. There was little-to-no evidence that sedentary behavior was associated with increased blood pressure and increased blood lipids.

Cardiorespiratory fitness and risk of prostate cancer: findings from the Aerobics Center Longitudinal Study.

OBJECTIVE To examine the association between cardiorespiratory fitness (CRF) and risk of incident prostate cancer (PrCA). METHODS Participants were 19,042 male subjects in the Aerobics Center Longitudinal Study (ACLS), ages 20-82years, who received a baseline medical examination including a maximal treadmill exercise test between 1976 and 2003. CRF levels were defined as low (lowest 20%), moderate (middle 40%), and high (upper 40%) according to age-specific distribution of treadmill duration from the overall ACLS population. PrCA was assessed from responses to mail-back health surveys during 1982-2004. Cox proportional hazards regression models, adjusted for potential confounders, were used to compute hazard ratios (HRs), 95% confidence intervals (95% CIs), and incidence rates (per 10,000 person-years of follow-up). RESULTS A total of 634 men reported a diagnosis of incident PrCA during an average of 9.3 ± 7.1 years of follow-up. Adjusted HRs (95% CIs) in men with moderate and high CRF relative to low CRF were, 1.68 (1.13-2.48) and 1.74 (1.15-2.62), respectively. The positive association between CRF and PrCA was observed only in the strata of men who were not obese, had ≥ 1 follow-up examination, or who were diagnosed ≤ 1995. CONCLUSIONS Rather than revealing a causal relationship, the unexpected positive association observed between CRF and incident PrCA is most likely due to a screening/detection bias in more fit men who also are more health-conscious. Results have important implications for understanding the health-related factors that predispose men to receive PrCA screening that may lead to over-detection of indolent disease.

Objectively measured sedentary behavior in preschool children: comparison between Montessori and traditional preschools.

BackgroundThis study aimed to compare the levels of objectively-measured sedentary behavior in children attending Montessori preschools with those attending traditional preschools.MethodsThe participants in this study were preschool children aged 4 years old who were enrolled in Montessori and traditional preschools. The preschool children wore ActiGraph accelerometers. Accelerometers were initialized using 15-second intervals and sedentary behavior was defined as <200 counts/15-second. The accelerometry data were summarized into the average minutes per hour spent in sedentary behavior during the in-school, the after-school, and the total-day period. Mixed linear regression models were used to determine differences in the average time spent in sedentary behavior between children attending traditional and Montessori preschools, after adjusting for selected potential correlates of preschoolers’ sedentary behavior.ResultsChildren attending Montessori preschools spent less time in sedentary behavior than those attending traditional preschools during the in-school (44.4. min/hr vs. 47.1 min/hr, P = 0.03), after-school (42.8. min/hr vs. 44.7 min/hr, P = 0.04), and total-day (43.7 min/hr vs. 45.5 min/hr, P = 0. 009) periods. School type (Montessori or traditional), preschool setting (private or public), socio-demographic factors (age, gender, and socioeconomic status) were found to be significant predictors of preschoolers’ sedentary behavior.ConclusionsLevels of objectively-measured sedentary behavior were significantly lower among children attending Montessori preschools compared to children attending traditional preschools. Future research should examine the specific characteristics of Montessori preschools that predict the lower levels of sedentary behavior among children attending these preschools compared to children attending traditional preschools.

Association between objectively measured sedentary behavior and body mass index in preschool children

Objective:To determine the association between accelerometry-derived sedentary behavior and body mass index (BMI) z-score in preschool children, and to determine whether the association changed when applying three different accelerometry cutpoints for sedentary behavior.Design and subjects:Cross-sectional design. Data came from two completed studies: Children’s Activity and Movement in Preschool Study (CHAMPS) and the Environmental Determinants of Physical Activity in Preschool Children (EDPAPC) study. Children of ages 3–5 years with complete data on sedentary behavior, BMI z-score, physical activity and other covariates were included in the analyses (N=263 in CHAMPS and N=155 in EDPAPC). Accelerometry data were summarized as time spent in sedentary behavior (min h−1) using three different cutpoints developed specifically for preschool children (<37.5, <200 and <373 counts per 15 s). Linear mixed regression models were used to determine the association between time spent in sedentary behavior and BMI z-score; age, gender, race, parental education, preschools and moderate-to-vigorous physical activity (MVPA) were included as covariates.Results:In both CHAMPS and EDPAPC studies, no independent association between time spent in sedentary behavior and BMI z-score was observed after adjusting for MVPA. The observed null association between sedentary behavior and BMI z-score was maintained even with different sedentary behavior cutpoints.Conclusions:Regardless of cutpoints used, accelerometry-derived sedentary behavior was not independently associated with BMI z-score in two independent samples of preschool children. Longitudinal studies addressing this research question are needed.