Introduction
Self-reported daytime napping is associated with various adverse health outcomes. We examined whether actigraphy-measured objective daytime napping behaviors predict all-cause mortality in middle-to-older aged adults in the UK Biobank.
Methods
We studied 86,565 participants (baseline age=63 years, SD=8, range: 43-79; 57% female) in the UK Biobank who did not have shiftwork history, completed a 7-day actigraphy monitoring, and had data linked to mortality registeries. We implemented the Cole-Kripke algorithm to identify daytime sleep episodes from actigraphy and computed the following nap metrics: (1) mean nap duration between 9am-7pm; (2) intra-individual variability across days (individual SD) in nap duration; (3) timing of naps quantified as the percentage of nap duration in each 2-h bin between 9am-7pm (i.e., 9-11am, 11am-1pm, 1-3pm, 3-5pm, 5-7pm). Nap variables were square-root transformed to correct for right skewness and standardized for interpretation. Cox proportional hazards models were performed to test the associations between napping metrics and all-cause mortality, adjusting for demographics, BMI, smoking, alcohol consumption, comorbidities, nighttime sleep duration, and chronotype.
Results
Median nap duration was 0.40 hours/day (IQR=0.19-0.77), and intra-individual variability of nap duration was 0.39 hours (IQR=0.19-0.69). Thirty-four percent (IQR=12%-52%) of the naps were taken between 9-11am, 10% (IQR=0%-17%) between 11am-1pm, 14% (IQR=0%-22%) between 1-3pm, 19% (IQR=1%-29%) between 3-5pm, and 22% (IQR=4%-32%) between 5-7pm. During an up to 8-year follow-up, 2,950 (3.4%) participants died, and among them, the average survival time was 4.19 (range: 0.03-8.15) years after baseline. Longer nap duration (for 1-SD, HR=1.20, 95%CI: 1.16-1.24, p< 0.0001), greater intra-individual variability (for 1-SD, HR=1.14, 95%CI: 1.10-1.18, p< 0.0001), and higher percentage of naps between 11am-1pm and between 1-3pm were associated with mortality (for 1-SD, 11am-1pm: HR=1.07, 95%CI: 1.03-1.11, p=0.0005; 1-3pm: HR=1.07, 95%CI: 1.03-1.12, p=0.0002).
Conclusion
Longer naps, greater intra-individual variability in daytime nap, and higher percentages of naps around noon and in the early afternoon are associated with greater mortality risks. These findings highlight the potential importance of considering napping behaviors in risk stratification of mortality in middle-to-older aged adults. Incorporating actigraphy-based nap assessments into clinical and public health practices may provide novel opportunities for early risk identification and personalized interventions to promote longevity.
https://academic.oup.com/sleep/article/48/Supplement_1/A152/8135607
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