Abstract
Today’s modern society is exposed to artificial electric lighting in addition to the natural light-dark cycle. Studies assessing the impact of electric light exposure on sleep and its relation to work hours are rare due to the ubiquitous presence of electricity. Here we report a unique study conducted in two phases in a homogenous group of rubber tappers living and working in a remote area of the Amazon forest, comparing those living without electric light (n = 243 in first phase; n = 25 in second phase) to those with electric light at home (n = 97 in first phase; n = 17 in second phase). Questionnaire data (Phase 1) revealed that rubber tappers with availability of electric light had significantly shorter sleep on work days (30 min/day less) than those without electric light. Analysis of the data from the Phase 2 sample showed a significant delay in the timing of melatonin onset in workers with electric light compared to those without electric light (p < 0.01). Electric lighting delayed sleep onset and reduced sleep duration during the work week and appears to interfere with alignment of the circadian timing system to the natural light/dark cycle.
Highlights
Today there is no doubt of the importance of the light/dark cycle in the regulation and synchronization of the circadian timing system
A study of adults camping in tents under natural light/dark conditions followed by a period living in a laboratory with electric lighting showed a change in phase of entrainment, changes in sleep timing as well as reduced exposure to sunlight and widespread use of electric light in the constructed laboratory environment[16]
The study was done in two phases, a questionnaire phase (Phase 1; n = 97 with electric light and n = 243 without electric light), and an objective measures phase (Phase 2; n = 17 with electric light and n = 25 without electric light), where data regarding sleep-wake patterns, melatonin timing and light exposure were collected during work days and days-off
Summary
Today there is no doubt of the importance of the light/dark cycle in the regulation and synchronization of the circadian timing system. Modern society promotes a lifestyle that works against circadian alignment, with increased exposure to artificial light and use of electronic equipment, both only possible due to the advent of electricity. A study of adults camping in tents under natural light/dark conditions followed by a period living in a laboratory with electric lighting showed a change in phase of entrainment, changes in sleep timing as well as reduced exposure to sunlight and widespread use of electric light in the constructed laboratory environment[16]. In 2003, the Brazilian government created a program called “Light for everybody”, and formed partnerships to fulfil this commitment The goal of this governmental program was to install electricity in all houses (including residences, schools, and public places) in the country, that were still without electricity.
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