
Natural Sleep and Its Seasonal Variations in Three Pre-Industrial Societies - andyjohnson0
http://www.cell.com/current-biology/abstract/S0960-9822(15)01157-4
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andyjohnson0
Summary:

How did humans sleep before the modern era? Because the tools to measure sleep
under natural conditions were developed long after the invention of the
electric devices suspected of delaying and reducing sleep, we investigated
sleep in three preindustrial societies [ 1–3 ]. We find that all three show
similar sleep organization, suggesting that they express core human sleep
patterns, most likely characteristic of pre-modern era Homo sapiens. Sleep
periods, the times from onset to offset, averaged 6.9–8.5 hr, with sleep
durations of 5.7–7.1 hr, amounts near the low end of those industrial
societies [ 4–7 ]. There was a difference of nearly 1 hr between summer and
winter sleep. Daily variation in sleep duration was strongly linked to time of
onset, rather than offset. None of these groups began sleep near sunset, onset
occurring, on average, 3.3 hr after sunset. Awakening was usually before
sunrise. The sleep period consistently occurred during the nighttime period of
falling environmental temperature, was not interrupted by extended periods of
waking, and terminated, with vasoconstriction, near the nadir of daily ambient
temperature. The daily cycle of temperature change, largely eliminated from
modern sleep environments, may be a potent natural regulator of sleep. Light
exposure was maximal in the morning and greatly decreased at noon, indicating
that all three groups seek shade at midday and that light activation of the
suprachiasmatic nucleus is maximal in the morning. Napping occurred on <7% of
days in winter and <22% of days in summer. Mimicking aspects of the natural
environment might be effective in treating certain modern sleep disorders.

