Age-related patterns in distal skin temperature during naps

STUDY OBJECTIVES: Naps are common worldwide; despite their prevalence, physiological changes during naps are less well-characterized than during nighttime sleep. We aimed to characterize napping patterns and their associated physiological changes across age groups. METHODS: We used longitudinal wearable device data from 20 027 individuals from the TemPredict Study to assess (1) napping frequency and timing and (2) distal skin temperature changes around naps. RESULTS: Older age groups napped more frequently and consistently throughout the week. Individuals aged 30-49 years showed the greatest increase in nap frequency from weekdays to weekends, whereas younger (18-19 years) and older (≥60 years) age groups showed the smallest increases. Sleep timing and distal skin temperature rhythms appeared tightly coupled, even during the daytime. Both sleep timing and distal skin temperature rhythms appeared phase-delayed among younger age groups relative to older age groups. Distal skin temperature was higher during naps on weekends relative to weekdays. Older individuals (≥65 years) had lower distal skin temperatures during naps relative to younger individuals (≤30 years) (weekends: p < .0001; δ = -0.20; weekdays: p < .0001; δ = -0.19). Longer naps were generally associated with greater distal skin temperature before napping, especially among younger individuals (≤30 years). CONCLUSION: We observed age-related differences in napping patterns and distal skin temperature around and during naps. Future research should examine whether such distal skin temperature changes around naps relate to sleep pressure and age-related disease risk.