Sleep variability and nighttime activity among Tsimane forager-horticulturalists

Area of Science:

• Anthropology
• Sleep Science
• Human Ecology

Background:

• A prevailing assumption in sleep research posits that normal human sleep exhibits high night-to-night consistency.
• However, empirical data on intra-individual sleep variation within small-scale subsistence populations remain scarce.
• This study investigates sleep variability in the Tsimane forager-horticulturalists of Bolivia.

Purpose of the Study:

• To assess the extent of nightly variation in sleep patterns among Tsimane adults.
• To identify potential drivers of intra-individual sleep variability in this population.
• To compare Tsimane sleep variation patterns with those observed in industrialized societies.

Main Methods:

• Actigraphy was employed to record sleep patterns in 120 Tsimane adults (67 female, aged 18-91) over an average of 4.9 nights per individual.
• Sleep duration, onset, and offset times were analyzed using intra-class correlations and average deviation metrics.
• Data were collected using Actigraph GT3X and Philips Respironics Actiwatch 2 devices.

Main Results:

• Intra-individual variation accounted for 69% of the total variation in sleep duration, while inter-individual differences explained only 31%.
• No significant day-of-the-week variations in Tsimane sleep duration were observed.
• Highly variable sleep onset times, influenced by activities like hunting, fishing, housework, and TV, were the primary drivers of nightly sleep duration variability, particularly in men.

Conclusions:

• Tsimane sleep variation, comparable in magnitude to that in the United States, is driven by fluctuating sleep onset times rather than weekend "sleeping-in."
• This pattern suggests that Tsimane sleep variability may represent adaptive adjustments to the opportunity costs of nighttime activities.
• Findings challenge the universality of high sleep consistency as a marker of normal sleep and highlight the role of ecological factors.