BACKGROUND: Body composition assessment aids evaluation of energy stores and the impact of diseases and interventions on child growth. Current U.S. pediatric reference ranges from the National Health and Nutrition Examination Survey (NHANES) include 20% of children with obesity, BMI ≥95 percentile.

OBJECTIVE: To develop dual energy x-ray absorptiometry (DXA) based reference ranges in a diverse cohort with low obesity prevalence from the Bone Mineral Density in Childhood Study (BMDCS).

DESIGN: This is a secondary analysis of a longitudinal, prospective, observational cohort. Healthy children (height and BMI within 3 to 97 percentiles, ages 5-19y at enrollment), from 5 U.S. centers were measured annually for up to 7 visits. Whole body scans were acquired using Hologic scanners. A subsample underwent repeat measurements to determine precision. We generated reference ranges for appendicular and total lean soft-tissue mass index (LSTM Index), fat mass index (FMI), and other body composition measures. Resulting curves were compared to NHANES and across subgroups. Sex and age-specific equations were developed to adjust body composition Z-scores for height Z-score.

RESULTS: We obtained 9,846 scans on 2011 participants (51% female, 22% Black, 17% Hispanic, 48% White, 7% Asian/Pacific Islander, 6% with obesity). Precision (percent coefficient of variation) ranged from 0.7 to 1.96%. Median and -2SD curves for BMDCS and NHANES were similar, but NHANES +2SD LSTM Index and FMI curves were distinctly greater than the respective BMDCS curves. Subgroup differences were more extreme for appendicular LSTM Index-Z (mean±sd: Asian -0.52±0.93 vs Black 0.77±0.87) than for FMI-Z (Hispanic 0.29±0.98 vs Black -0.14±1.1) and were smaller for Z-scores adjusted for height Z-score.

CONCLUSIONS: These reference ranges add to sparse normative data regarding body composition in children and adolescents, and are based on a cohort with an obesity prevalence similar to current BMI charts. Awareness of subgroup differences aid in interpreting results.

<p><strong>STUDY OBJECTIVES: </strong>Over 75% of US high school students obtain insufficient sleep, placing them at risk for adverse health outcomes. Identification of modifiable determinants of adolescent sleep is needed to inform prevention strategies, yet little is known about the influence of the built environment on adolescent sleep.</p>

<p><strong>METHODS: </strong>In this prospective study, actigraphy was used to assess sleep outcomes among 110 adolescents for 14 days each in eighth and ninth grades: duration (hours/night), onset and offset, and sleeping ≥8 hours. Home addresses were linked to built environment exposures: sound levels, tree canopy cover, street density, intersection density, population density, and housing density. Mixed-effects regression estimated associations of built environment measures with sleep outcomes, adjusting for sex, race, parent education, household income, household size, grade, weeknight status, and neighborhood poverty.</p>

<p><strong>RESULTS: </strong>A 1-standard deviation (SD) increase in neighborhood sound was associated with 16 minutes later sleep onset (β = 0.28; 95% confidence interval (CI): 0.06, 0.49) and 25% lower odds of sleeping for ≥8 hours (odds ratio (OR) = 0.75, 95% CI: 0.59, 0.96). A 1-SD increase in neighborhood tree canopy was associated with 18 minutes earlier sleep onset (β = -0.31, 95% CI: -0.49, -0.13) and 10 minutes earlier sleep offset (β= -0.17, 95% CI: -0.28, -0.05). No associations were observed for density-based exposures.</p>

<p><strong>CONCLUSIONS: </strong>Higher neighborhood sound level was associated with lower odds of sufficient sleep, while higher tree canopy cover was associated with more favorable sleep timing. Neighborhood sound levels and tree canopy cover are potential targets for policies and interventions to support healthier sleep among adolescents.</p>

<p><strong>PURPOSE: </strong>The purpose of the study was to quantify changes in sleep during the middle-to-high school transition and determine if changes in sleep differ by sociodemographic characteristics.</p>

<p><strong>METHODS: </strong>Adolescents were enrolled in eighth grade and followed into ninth grade (N&nbsp;= 110; 2,470 nights observed). The outcomes were actigraphy-estimated sleep duration, sleep onset, sleep offset, and sleep sufficiency (≥8&nbsp;hours of sleep). The exposures were school grade (eighth or ninth), school night status (school or nonschool), sex (female or male), and race (white, black, or other).</p>

<p><strong>RESULTS: </strong>On school nights, sleep duration declined by 25.8&nbsp;minutes per night (p &lt; .001) from eighth to ninth grade. There was no change in sleep duration on nonschool nights. Timing of sleep onset was 22.2&nbsp;minutes later on school nights (p &lt; .001) and 17.4&nbsp;minutes later on nonschool nights (p&nbsp;&lt;&nbsp;.001) in ninth grade. Timing of sleep offset did not change on school mornings but was 22.2&nbsp;minutes later on nonschool mornings (p &lt; .001) in ninth grade. The proportion of school nights (and nonschool nights) with sleep duration ≥8&nbsp;hours was 9.4% (38.3%) in eighth grade and 5.7% (35.9%) in ninth grade. The odds of sleeping ≥8&nbsp;hours per night was 42% lower in ninth grade, compared toeighth grade (odds ratio&nbsp;= .58; 95% confidence interval: .37, .91). Males were 59% less likely to sleep ≥8&nbsp;hours per night. Black adolescents were 51% less likely to sleep ≥8&nbsp;hours per night.</p>

<p><strong>CONCLUSIONS: </strong>Insufficient sleep is highly prevalent, especially on school nights and among male and black adolescents, and this problem worsens with the transition to high school.</p>