Social jetlag is associated with cardiorespiratory fitness in male but not female adolescents

Introduction: Cardiorespiratory fitness (CRF) is a vital sign that can improve risk classification for adverse health outcomes. While lifestyle-related factors are associated with CRF, few have examined the influ-ence of sleep characteristics, especially in youths. Social jetlag, a mismatch between one's biological clock and sleep schedule, is prevalent in adolescents and associated with increased adiposity, though its relationship with CRF is unclear. Objective: To quantify the relationship between social jetlag and CRF, independent of other sleep characteristics. Methods: This cross-sectional sample includes 276 New Zealand adolescents (14-18 years, 52.5% female). CRF (VO2max) was estimated from a 20-m multi-stage shuttle run. Average sleep duration, sleep disturbances, social jetlag, physical activity, and the number of bedroom screens were estimated from validated self-report surveys. Social jetlag is the difference in hours between the midpoint of sleep during weekdays (school) and weekend days (free). Combined and sex-stratified linear regression assessed the association between sleep outcomes and CRF, controlling for relevant covariates. Results: Males slept 17.6 min less, had less sleep disturbances, and a 25.1-min greater social jetlag than their female peers (all p < 0.05). A 1-h increase in social jetlag was associated with a 0.72 ml/kg/min decrease in VO2max (95% CI:-1.31,-0.14), independent of other sleep variables, which were not associated with CRF. Sex-specific models indicated an association in males (B-0.93, 95% CI:-1.76,-0.09), but not females (B-0.32, 95% CI:-1.18, 0.55). Conclusions: Social jetlag is negatively associated with CRF in adolescent males and may be a simple, measurable target for public health interventions. (c) 2020 Elsevier B.V. All rights reserved.