Seasonal synchronization of sleep timing in industrial and pre-industrial societies

José María Martín-Olalla

doi:10.1038/s41598-019-43220-8

Abstract

Artificial light has reshaped human sleep/wake cycle in industrial societies and raised concern on the misalignment of this cycle relative to the light and dark cycle. This manuscript contrasts sleep timing in extratropical, industrial societies (data from eight national time use surveys in countries with Daylight Saving Time —DST— regulations) and Subtropical, pre-industrial societies with and without access to artificial light (data from nine locations coming from seven previous reports) against the cycle of light and dark. Within the two process model of sleep, results show sleep onset and sleep offset keep bound to each other by the homeostatic process. In winter, the photoreceptive process aligns the phase of the sleep/wake cycle to sunrise. As a result the phase increasingly lags with increasing latitude up to a delay of 120 min at 55° latitude. In summer, the homeostatic process still binds sleep onset to speep offset but DST rules in industrialized societies reduce the lag by one third to 40 min at 55° latitude. Sleep timing is then stationary with latitude. The phase of the sleep/wake cycle is then governed by natural trends and no clues of misalignment are revealed.

Highlights

Artificial light has reshaped human sleep/wake cycle in industrial societies and raised concern on the misalignment of this cycle relative to the light and dark cycle
This section will put forward the seasonal differences in sleep timing and will contrast sleep timing against the natural gradients m = 0 and m = ±β through three different methods: first a visualization of data (Fig. 2); multiple binning analyses (Fig. 3); and univariate analyses and multiple bivariate analyses (Table 4)
They include: (1) sample gradient ms and (2) its confidence interval CI both measured in units of β = 30 min h−1, except when the response is solar altitude, in which case they are measured in degrees per hour, the parentheses show half the amplitude of the confidence intervals; (3) the probabilistic value (p-value); (4) the coefficient of determination; and (5) possible outliers —experimental data whose confidence residual excludes zero

Summary

Introduction

Artificial light has reshaped human sleep/wake cycle in industrial societies and raised concern on the misalignment of this cycle relative to the light and dark cycle. The homeostatic process still binds sleep onset to speep offset but DST rules in industrialized societies reduce the lag by one third to 40 min at 55° latitude. It is a wide understood that artificial light and industrialization has reshaped the human sleep/wake cycle[2] by altering the way humans receipt light during the scotoperiod. In the past few years several studies have addressed the sleep timing in societies with different degrees of industrialization, trying to find clues which help understanding the way modern artificial light has altered sleep timing

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Discussion

Conclusion