Hadza sleep biology: Evidence for flexible sleep-wake patterns in hunter-gatherers.
Level 4 - case-series / case-control
Observational field study using actigraphy in a single population cohort.
PubMed 28063234 · doi:10.1002/ajpa.23160
What was done
Sleep-wake patterns were measured using actigraphy in 33 Hadza hunter-gatherer volunteers in Tanzania across a total of 393 participant-days. Linear mixed effects modeling was used to identify ecological predictors of sleep duration and quality, and functional linear modeling was used to characterize 24-hour time-averaged circadian patterns.
What was found
Hadza participants exhibited an average sleep duration of 6.25 hours and a sleep efficiency of 68.9%. Sleep duration was negatively influenced by greater activity, age, light exposure (lux), and moon phase, and was positively influenced by increased day length and mean nighttime temperature. The average daily nap ratio was 0.54 (SE = 0.05), with an average nap duration of 47.5 minutes (SE = 2.71; n = 139 naps).
Why it matters
This paper provides empirical actigraphy data from an equatorial foraging society, demonstrating that ancestral human sleep may have been flexible, environmentally entrained, and characterized by shorter nocturnal duration supplemented by opportunistic daytime naps.
Limits
The sample size is limited to 33 individuals from a single community. Comparisons to post-industrialized Western populations were descriptive without a concurrent control cohort, and sleep architecture was measured via actigraphy rather than polysomnography.
Cited by
- contradicts In hunter-gatherer tribes, the midpoint of the sleep phase occurs between midnight and 1:00 p.m. [sic].