Abstract
To investigate associations of bedtimes and sleep durations with adiposity levels in children and adolescents. Individual data were pooled for 12 247 children (5819 with follow-up adiposity at 2.3 ± 1.4 years post-baseline) and 3563 adolescents from 11 international studies. Associations between questionnaire-based sleep durations, bedtimes and four groups of combined bedtimes and sleep lengths (later-shorter [reference]/earlier-shorter/later-longer/earlier-longer) with measured adiposity (body mass index [BMI] and waist circumference z-scores) and weight status, were investigated. In children, longer sleep durations were consistently associated with lower adiposity markers, and earlier bedtimes were related to lower BMI z-score. Compared to sleeping <10h, longer baseline sleep duration favourably predicted Δwaist z-score in girls (≥10 and <11 h (β-coefficient (95% confidence interval [CI])): -0.06 (-0.12 to -0.01)) and boys (≥11 h: -0.10 [-0.18 to -0.01]). Combined groups that were defined by longer sleep (later-longer and earlier-longer sleep patterns) were associated with lower adiposity, and later-longer sleep favourably predicted Δwaist z-score in girls (-0.09 [-0.15 to -0.02]). In adolescents, longer sleep durations and earlier bedtimes were associated with lower BMI z-score in the whole sample, and also with lower waist z-score in boys. Combined groups that were characterized by earlier bedtimes were associated with the same outcomes. For example, earlier-shorter (-0.22 (-0.43 to -0.01) and earlier-longer (-0.16 (-0.25 to -0.06) sleep were both associated with lower BMI z-score. If the associations are causal, longer sleep duration and earlier bedtimes should be targeted for obesity prevention, emphasizing longer sleep for children and earlier bedtimes for adolescents.
Highlights
Cross-sectional studies, and meta-analyses of prospective studies, report that longer sleep duration is associated with lower adiposity and obesity risk in youth.[1,2,3] There is considerable heterogeneity in the results of individual prospective studies, and investigations rarely include adiposity markers other than weight-for-height indices, even though centrally stored adiposity is metabolically more harmful than total adiposity.[4]
Combined groups that were defined by longer sleep were associated with lower adiposity, and later-longer sleep favourably predicted Δwaist z-score in girls (À0.09 [À0.15 to À0.02])
Longer sleep durations and earlier bedtimes were associated with lower BMI z-score in the whole sample, and with lower waist z-score in boys
Summary
Cross-sectional studies, and meta-analyses of prospective studies, report that longer sleep duration is associated with lower adiposity and obesity risk in youth.[1,2,3] There is considerable heterogeneity in the results of individual prospective studies, and investigations rarely include adiposity markers other than weight-for-height indices, even though centrally stored adiposity is metabolically more harmful than total adiposity.[4]. Some studies even suggest that the associations are distinct from sleep duration.[12,13,14] This information could be pivotal in terms of refining obesity prevention efforts It may have important implications for sleep recommendations, which have historically focussed on duration as opposed to any other sleep parameter.[15] More studies are required to investigate sleep dimensions simultaneously, but it is challenging to investigate the independent or interactive effects of bedtimes and sleep durations, because they are often highly correlated. As are prospective investigations of sleep durations and bedtimes, to quantify the influence of both dimensions on youth adiposity over time.[6]
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