Circadian misalignment impacts the association of visceral adiposity with metabolic syndrome in adolescents.

STUDY OBJECTIVES: Although insufficient sleep is a risk factor for metabolic syndrome (MetS), the circadian timing of sleep (CTS) is also involved in cardiac and metabolic regulation. We examined whether delays and deviations in the sleep midpoint (SM), a measure of CTS, modify the association between visceral adipose tissue (VAT) and MetS in adolescents. METHODS: We evaluated 277 adolescents (median 16 years) who had at least 5 nights of at-home actigraphy (ACT), in-lab polysomnography (PSG), dual-energy X-ray absorptiometry (DXA) scan, and MetS score data. Sleep midpoint (SM), sleep irregularity (SI), and social jetlag (SJL) were examined as effect modifiers of the association between VAT and MetS, including waist circumference, blood pressure, insulin resistance, triglycerides, and cholesterol. Linear regression models adjusted for demographics, ACT-sleep duration, ACT-sleep variability, and PSG-apnea-hypopnea index. RESULTS: The association between VAT and MetS was significantly stronger (p-values for interactions < 0.001) among adolescents with a schooldays SM later than 4:00 (2.66 [0.30] points increase in MetS score), a SI higher than 1 hour (2.49 [0.30]) or a SJL greater than 1.5 hours (2.15 [0.36]), than in those with an earlier SM (<3:00; 1.76 [0.28]), lower SI (<30 minutes; 0.98 [0.70]), or optimal SJL (<30 minutes; 1.08 [0.45]). CONCLUSIONS: A delayed sleep phase, an irregular sleep-wake cycle, and greater social jetlag on schooldays identified adolescents in whom VAT had a stronger association with MetS. Circadian misalignment is a risk factor that enhances the impact of visceral obesity on cardiometabolic morbidity and should be a target of preventative strategies in adolescents.

Circadian Misalignment Impacts the Association of Visceral Adiposity With Elevated Blood Pressure in Adolescents.

BACKGROUND: Although insufficient sleep has been shown to contribute to obesity-related elevated blood pressure, the circadian timing of sleep has emerged as a novel risk factor. We hypothesized that deviations in sleep midpoint, a measure of circadian timing of sleep, modify the association between visceral adiposity and elevated blood pressure in adolescents. METHODS: We studied 303 subjects from the Penn State Child Cohort (16.2±2.2 years; 47.5% female; 21.5% racial/ethnic minority). Actigraphy-measured sleep duration, midpoint, variability, and regularity were calculated across a 7-night period. Visceral adipose tissue (VAT) was measured with dual-energy X-ray absorptiometry. Systolic blood pressure (SBP) and diastolic blood pressure levels were measured in the seated position. Multivariable linear regression models tested sleep midpoint and its regularity as effect modifiers of VAT on SBP/diastolic blood pressure levels, while adjusting for demographic and sleep covariables. These associations were also examined as a function of being in-school or on-break. RESULTS: Significant interactions were found between VAT and sleep irregularity, but not sleep midpoint, on SBP (P interaction=0.007) and diastolic blood pressure (P interaction=0.022). Additionally, significant interactions were found between VAT and schooldays sleep midpoint on SBP (P interaction=0.026) and diastolic blood pressure (P interaction=0.043), whereas significant interactions were found between VAT and on-break weekdays sleep irregularity on SBP (P interaction=0.034). CONCLUSIONS: A delayed and an irregular sleep midpoint during school and during free-days, respectively, increase the impact of VAT on elevated blood pressure in adolescents. These data suggest that deviations in the circadian timing of sleep contribute to the increased cardiovascular sequelae associated with obesity and that its distinct metrics require measurement under different entrainment conditions in adolescents.

Sleep variability and regularity as contributors to obesity and cardiometabolic health in adolescence.

OBJECTIVE: Adolescence is a developmental stage of critical changes in sleep and its circadian timing when the contribution of abnormal sleep variability (amount) and sleep regularity (timing) to obesity and its associated adverse cardiometabolic health outcomes appears to increase. The aim of this study was to summarize findings from studies conducted in adolescents examining both sleep variability and regularity in relation to obesity and cardiometabolic health. Gaps in research and potential causal pathways that future studies should examine are highlighted. RESULTS: Nightly deviations in sleep duration and sleep midpoint appear to contribute to the development of obesity and associated adverse cardiometabolic outcomes in youth. Studies show that increased sleep variability and irregularity are associated with obesity, decreased physical activity, dysregulated eating and inadequate diet, metabolic dysfunction, impaired cardiac autonomic balance, and elevated blood pressure in adolescents. CONCLUSIONS: A stable circadian timing of sleep is essential to the overall physical well-being of youth. Emerging evidence supports that sleep variability and circadian misalignment, including sleep irregularity, contribute to adverse obesity-related health outcomes early on in adolescence. Future studies should focus on the underlying behavioral and biological mechanisms in the causal pathway between day-to-day deviations in the amount and timing of sleep and obesity.