Introduction:
Cardiorespiratory fitness (CRF) has been highlighted by the AHA as a vital sign that can significantly improve risk classification for adverse health outcomes across the lifespan. While many lifestyle-related factors are known to influence CRF, including physical activity and sedentary behaviors, few have examined the relationship between sleep characteristics and CRF. Social jetlag (SJL), a characteristic of sleep habits that is particularly prevalent in adolescents, is a mismatch between an individual’s circadian clock and sleep schedule. SJL has been associated with adiposity and increased cardiometabolic risk, independent of sleep duration and quality, but has not been associated with CRF.
Objective:
To quantify the relationship between SJL and CRF, independent of other sleep characteristics.
Methods:
CRF, anthropometric, and lifestyle-related data were collected from 276 adolescents in Otago, New Zealand (14-18 years, n=145 [52.5%] female). CRF was expressed as VO
2max
(ml/kg/min) relative to body weight, estimated from a 20-meter multi-stage shuttle run. Lifestyle-related factors such as physical activity and the number of screens in the bedroom were quantified via an online lifestyle survey. Sleep variables including average sleep duration, sleep disturbances (trouble falling and staying asleep), and SJL were collected using the validated Sleep Habits Survey for Adolescents. SJL was measured as the difference in hours between the midpoint of sleep during week (school) days and on weekend (free) days. Linear regression assessed the association between each sleep outcome and CRF, controlling for (1) age, sex, school decile, fat mass, and the number of screens in the bedroom, and (2) moderate-to-vigorous intensity physical activity. Stratified analyses examined sex-specific relationships.
Results:
Mean (SD) VO
2max
was greater in males than females (48.47 [7.12] vs. 43.34 [5.62] ml/kg/min, p<.001). Sleep characteristics included a longer average sleep duration (9.48 [.92] vs. 9.19 [1.12] hours, p=.017), a greater occurrence of sleep disturbances (p=.001), and a lower SJL (1.67 [.08] vs. 2.09 [1.12] hours, p=.003) in females relative to their male peers. Multivariate analyses indicated that a one-hour increase in SJL was associated with a .71 ml/kg/min decrease in VO
2max
(95% CI: -1.30, -.11), independent of other sleep variables, which were not associated with CRF. Sex-specific models further indicated an association in males (b=-.93, 95% CI: -1.78, -.08), but an inconclusive association for females (b=-.29, 95% CI: -1.15, .57).
Conclusions:
SJL is negatively associated with CRF, with a more conclusive association in adolescent males, and may be a simple, measurable target for future public health interventions.
How does academic achievement relate to cardiorespiratory fitness, self-reported physical activity and objectively reported physical activity: a systematic review in children and adolescents aged 6–18 years
