Winter sleep extension and fragmentation in a South African agropastoral community

To examine seasonal sleep variation and assess the effects of gender, age, and environmental variables (Wet-Bulb Globe Temperature, moonlight, sunrise and sunset times) on sleep in a rural agropastoral community in South Africa with gender division of labor.

We collected actigraphy data from 114 participants (83 men, 31 women, 4750 nights) during summer and winter seasons in 2023. We used Bayesian hierarchical regression models to investigate drivers of sleep duration and quality.

Total Sleep Time was longer in winter (7.26 hours, SD = 1.0) compared to summer (6.40 hours, SD = 0.88), but so were Fragmentation Index and Wake After Sleep Onset. Higher Wet-Bulb Globe Temperature was associated with shorter Total Sleep Time, higher Fragmentation Index, and lower Sleep Efficiency. Greater moon illumination was correlated with shorter Total Sleep Time and reduced Fragmentation Index and Wake After Sleep Onset. Age was positively correlated with Total Sleep Time and Fragmentation Index among men, and older individuals had earlier sleep onset and offset than younger individuals. Compared to women, men had shorter and more disturbed sleep, especially in the winter, and were more impacted by Wet-Bulb Globe Temperature.

Sleep during the winter season was longer but more fragmented and of lower quality compared to the summer. Seasonal differences in extrinsic weather conditions and perceived risks operated on preexisting gendered labor and sleep disparities to drive seasonal sleep variation in this community. Future research should consider the disproportionate effects that environmental variables can have on sleep outcomes for different groups.