The influence of age- and sex-specific labor demands on sleep in Namibian agropastoralists.

OBJECTIVE: To understand the basics of sleep quality in a pastoralist population and to explore predictors of this variation.

DESIGN: Cross-sectional.

SETTING: Northern Namibia, dry seasons of 2016 and 2017.

PARTICIPANTS: The Himba, a nonindustrial seminomadic agropastoralist population without access to the electrical grid.

MEASUREMENTS: Using Actiwatch-2 devices, 75 participants completed 721 days of wear. We calculated sleep duration, efficiency, and activity counts before and after sunset/sunrise and onset/offset. Participants were also interviewed about sleeping arrangements and nighttime disruptions.

RESULTS: Himba show lower sleep duration and efficiency than other populations studied, and men had substantially lower duration and efficiency than women. Sex differences were not attenuated when napping was included with total sleep time. Age predicted longer sleep duration and lower evening and morning activity levels. Number of adult co-sleepers predicted increased sleep duration and efficiency in women. Livestock disturbance was not a commonly reported cause of nighttime waking.

CONCLUSIONS: These findings support predictions that pastoralist groups may have lower sleep quality than other subsistence populations, but this does not appear to be a consequence of noise from livestock. Instead, lower sleep quality appears to be the result of subsistence and social activities, particularly for men and young adults overall.