CoChat
Sign Up
Cited by 156Circadian rhythm and melatoninSleep and related disordersImpact of Light on Environment and Health

Access to Electric Light Is Associated with Shorter Sleep Duration in a Traditionally Hunter-Gatherer Community

Open access
de la Iglesia, Horacio O., Fernández-Duque, Eduardo, Golombek, Diego A., Lanza, Norberto, Duffy, Jeanne F., Czeisler, Charles A., Valeggia, Claudia R.·2015·Journal of Biological Rhythms
DOI 10.1177/0748730415590702PMC PMC5320422
Open this paper in CoChat — free account

Abstract

Access to electric light might have shifted the ancestral timing and duration of human sleep. To test this hypothesis, we studied two communities of the historically hunter-gatherer indigenous Toba/Qom in the Argentinean Chaco. These communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light. We fitted participants in each community with wrist activity data loggers to assess their sleep-wake cycles during one week in the summer and one week in the winter. During the summer, participants with access to electricity had a tendency to a shorter daily sleep bout (43 ± 21 min) than those living under natural light conditions. This difference was due to a later daily bedtime and sleep onset in the community with electricity, but a similar sleep offset and rise time in both communities. In the winter, participants without access to electricity slept longer (56 ± 17 min) than those with access to electricity, and this was also related to earlier bedtimes and sleep onsets than participants in the community with electricity. In both communities, daily sleep duration was longer during the winter than during the summer. Our field study supports the notion that access to inexpensive sources of artificial light and the ability to create artificially lit environments must have been key factors in reducing sleep in industrialized human societies.

AI snapshot

Written from the paper’s full text.

TL;DR

In two ethnically and socioculturally similar Toba/Qom communities in the Argentine Chaco, access to electric light was associated with later bedtimes and sleep onset and shorter sleep than living under natural light. The difference was larger in winter, and both communities slept longer in winter than in summer.

Key findings

  • In summer, the electricity community had a tendency toward a shorter daily sleep bout by 43 ± 21 min than the no-electricity community; this was significant by a 1-tailed Student t test (t10 = 2.1, p = 0.03) but not in the Bonferroni post hoc comparison. The difference was due to later bedtime (68 ± 24 min) and sleep onset (63 ± 25 min), with similar sleep offset and rise time.
  • In winter, the no-electricity community slept 56 ± 17 min longer than the electricity community, again due to earlier bedtime (59 ± 20 min) and sleep onset (54 ± 20 min), with similar sleep offset and rise time.
  • Both communities had longer sleep duration in winter than summer; the no-electricity community averaged 7 h in summer and nearly 8.5 h in winter. The discussion states the electricity community slept approximately 40 min less in summer and about an hour less in winter.
  • Winter evening light exposure was higher in the electricity community, whereas summer evening light exposure was higher in the no-electricity community.

Methods

  • Field actigraphy study in two Western Toba/Qom communities in Formosa, Argentina: one with 24-h access to electricity and one without electricity, located ~50 km apart. Data were collected near the summer solstice (November 24–December 2, 2012) and winter solstice (August 7–21, 2013).
  • Participants were adults and adolescents ages 14–49 years of both sexes. Summer: 6 participants per community over 6–8 days. Winter: 11 electricity and 8 no-electricity participants over 4–13 days. Wrist Actiwatch-L loggers recorded activity and light at 1-min intervals, averaged into 20-min bins; sleep diaries recorded bedtime, rise time, naps, and travel.
  • Sleep parameters were analyzed with 2-way ANOVA with factors electricity and season, with Bonferroni correction for significant effects; activity and light waveforms were analyzed with 2-way ANOVA with factors electricity and time, and variance was tested with the Bartlett test.

Limitations

  • Stated by the authors: the field study could not manipulate light exposure as an independent variable, so it can only establish relationships between electricity access and sleep patterns; electricity was also associated with a more comfortable, protected living environment and televisions; the number of participants, especially in summer, was relatively small; daily habit differences could contribute, though housing and social life were similar.
  • Stated by the authors: sleep was sampled in both seasons for only 2 no-electricity participants and 1 electricity participant, preventing repeated-measures statistical tests; small sample size also prevented analysis of age or sex effects.
  • Evident from the text: the observational design cannot establish causality, and there were sample imbalances, including a trend for the no-electricity group to be younger (p = 0.07 for electricity) and a winter electricity group that was 73% female.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1177/0748730415590702

Cites

Statistics

Nothing to recompute.

Claims the paper makes

0 of 6 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    During the winter, both communities experienced similar sleep offset and rise time.

    “however, both groups experienced a similar sleep offset and rise time within each season”
    Quote in the paperNot a substantial claim
  • Findingown data

    During the summer, both communities experienced similar sleep offset and rise time.

    “however, both groups experienced a similar sleep offset and rise time within each season”
    Quote in the paperNot a substantial claim
  • Findingown data

    During the summer, the mean activity waveforms showed less variability in locomotor activity levels in the NO-electricity than in the Electricity community (SD = 138 vs. 209; Bartlett test, F = 50, p < 0.0001).

    “The mean activity waveforms showed less variability in locomotor activity levels in the NO-electricity than in the Electricity community (SD = 138 vs. 209; Bartlett test, F = 50, p < 0.0001).”
    Quote in the paperNot a substantial claim
  • Findingreasoning

    During both seasons, the start of the rest phase was less synchronous in the Electricity community than in the NO-electricity community.

    “During both seasons, the start of the rest phase was less synchronous in the Electricity community than in the NO-electricity community.”
    Quote in the paperNot a substantial claim
  • Findingown data

    During the summer, the NO-electricity community had an earlier daily bedtime than the Electricity community, by 68 ± 24 min.

    “In both seasons, the longer duration of sleep in the NO-electricity community was due to a significantly earlier bedtime (summer: 68 ± 24 min; winter: 59 ± 20 min) and sleep onset (summer: 63 ± 25 min; winter: 54 ± 20 min) than in the Electricity community”
    Quote in the paperSubstantial claim
  • May combine two claims. 18
  • The quote only partly states this claim. 1
  • Classified as probably not a substantial claim. 8

  • May combine two claims.

    Findingown data

    Sleep duration averaged 7 h in summer and nearly 8.5 h in winter in the community without access to electric light.

    “We found that sleep duration averaged 7 h in summer and nearly 8.5 h in winter in the community without access to electric light.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    During the winter, the variance for sleep onset was greater for the Electricity group than the NO-electricity group, but not during the summer.

    “Interestingly, the variance for sleep onset was greater for the Electricity group than the NO-electricity group in the winter (F10,7 = 5.5, p = 0.03) but not in the summer (F5,5 = 1.3, p = 0.8).”
    Quote in the paperNot a substantial claim

  • The quote only partly states this claim.

    Findingown data

    During the summer, when focusing on evening hours, the NO-electricity group was exposed to light of higher intensity than the Electricity group.

    “When we focused our comparison of light exposure between the 2 groups on the evening hours, we found that the NO-electricity group was exposed to light of higher intensity (Fig. 2).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    During the winter, the NO-electricity community slept on average 56 ± 17 min more than the Electricity community; the difference was statistically significant.

    “During the winter, the NO-electricity group slept on average 56 ± 17 min more than did the Electricity community (Fig. 1D); the difference was statistically significant.”
    • Also stated in: § Abstract · plain
      “In the winter, participants without access to electricity slept longer (56 ± 17 min) than those with access to electricity”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    The difference in sleep timing between the two communities differed with season, with the community with electricity sleeping approximately 40 min less in summer and an hour less in winter than the community without electricity.

    “This difference in sleep timing between the 2 communities also differed with season, with the community who had access to electricity sleeping approximately 40 min less in summer and an hour less in winter than the community without electricity.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductreasoning

    The field study cannot manipulate light exposure as an independent variable, and therefore can only establish relationships between access to electric light and sleep patterns.

    “Specifically, we cannot manipulate light exposure as an independent variable, and therefore we can only establish relationships between the access to electric light and sleep patterns.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductnone given

    The type of housing, daily chores participants are involved in, and social behavior are similar for both communities.

    “Importantly, the type of housing, daily chores participants are involved in, and social behavior are similar for both communities.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning

    During the winter, the onset of sleep is more variable in the Electricity community, likely as a result of each participant's choice of time to turn the lights off and go to sleep.

    “This is clearly reflected by the fact that during the winter, the onset of sleep is more variable in the Electricity community, which is likely the result of each participant's choice of time to turn the lights off and go to sleep.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisenone given

    The two communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light.

    “These communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    A 2-way analysis of variance on ages revealed no statistically significant effects of season, electricity, or the interaction, although there was a trend for the NO-electricity group to be younger.

    “A 2-way analysis of variance on the ages revealed no statistically significant effects of season, electricity, or the interaction, although there was a trend for the NO-electricity group to be younger (F1,27 = 3.44, p = 0.07 for electricity; F1,27 = 2.1, p = 0.16 for season; F1,27 = 1.9, p = 0.18 for the interaction).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The number of participants, particularly for the summer study, is relatively small.

    “We are aware that the number of participants, particularly for the summer study, is relatively small.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    Due to the small sample size for each category, the statistical effects of age or sex were not analyzed.

    “Due to the small sample size for each category, we did not analyze the statistical effects of age or sex.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductnone given

    Both communities live in very similar types of housing and have a similar social life, with large family groups that share a common piece of land with several houses.

    “Finally, although differences in daily habits between the 2 communities studied could contribute to our results, both communities live in very similar types of housing and have a similar social life, with large family groups that share a common piece of land with several houses.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data

    Access to electricity in the Toba/Qom communities is associated with later bedtimes and sleep onsets but not with later sleep-offset or rise times, leading to a shorter daily sleep duration than in individuals without access to electricity.

    “We found that access to electricity in traditionally hunter-gatherer Toba/Qom communities is associated with later bedtimes and sleep onsets but not with later sleep-offset or rise times, leading to a shorter daily sleep duration than in individuals without access to electricity.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductown data

    The statistically significant difference supports the prespecified hypothesis that electricity delays sleep onset and shortens sleep.

    “This statistically significant difference supports the prespecified hypothesis that electricity delays sleep onset and shortens sleep.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationcitation

    The winter sleep duration in the community without access to electric light is longer than that typically reported from individuals in industrialized societies, while the summer sleep duration is not.

    “While the winter sleep duration is longer than that typically reported from individuals in industrialized societies, the summer time duration is not (Ohayon et al., 2004; Reyner et al., 1995; Roffwarg et al., 1966).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites Ohayon et al., 2004

      Not checked in the free run.

    • cites Reyner et al., 1995

      Not checked in the free run.

    • cites Roffwarg et al., 1966

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductnone given

    All groups had 50% female participants, except for the winter Electricity group, which included 73% female participants.

    “All groups had 50% of female participants, except for the winter Electricity group, which included 73% of female participants.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    Access to electricity has allowed humans to extend the evening light hours, thereby delaying the time of sleep onset and reducing daily sleep duration.

    “Our findings are consistent with the hypothesis that access to electricity has allowed humans to extend the evening light hours, thereby delaying the time of sleep onset and reducing daily sleep duration (Czeisler, 2013).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites Czeisler, 2013

      Not checked in the free run.

    • Rests on an assumption: Access to electricity is the primary cause of the observed differences in sleep timing and duration, rather than other lifestyle or environmental differences between the communities.

  • May combine two claims.

    Interpretationown data

    Individuals in the community with access to electricity were exposed to brighter light intensities during the winter evenings, suggesting that their later sleep onset and shorter sleep duration are the result of their access to electric light.

    “Examination of light levels in the 2 groups revealed that individuals in the community with access to electricity were exposed to brighter light intensities during the winter evenings, suggesting that their later sleep onset and shorter sleep duration are the result of their access to electric light.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: Access to electricity is the primary cause of the observed differences in sleep timing and duration, rather than other lifestyle or environmental differences between the communities.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data

    Sleep was sampled in both seasons for only 2 participants in the NO-electricity community and 1 in the Electricity community, preventing repeated-measures statistical tests.

    “Sleep was sampled in both seasons for only 2 participants in the NO-electricity community and 1 in the Electricity community, preventing us from carrying out repeated-measures statistical tests.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisereasoning

    People in both communities share the same ethnohistorical past; people are related by blood both within and between communities.

    “People in both communities share the same ethnohistorical past. In fact, people in the Electricity community originated from a few families who migrated from the NO-electricity community and its surroundings in the early 1990s; people are related by blood both within and between communities.”
    Quote in the paperSubstantial claim
21 of 21

  • The paper relies on this without support.

    The traditionally hunter-gatherer Toba/Qom group represents a proxy for the human ancestral sleep-wake cycle.

    “Our study shows that the presence of electricity reduces sleep—a salient trait in human biology—in a traditionally hunter-gatherer group, a condition that represents a proxy for the human ancestral sleep-wake cycle.”

  • The paper relies on this without support.

    Access to electricity is the primary cause of the observed differences in sleep timing and duration, rather than other lifestyle or environmental differences between the communities.

    “Specifically, we cannot manipulate light exposure as an independent variable, and therefore we can only establish relationships between the access to electric light and sleep patterns.”
    “Electricity was not only associated with a readily available source of artificial light but was also associated with a more comfortable and protected living environment.”
2 of 2

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

The citation lists haven’t been fetched yet

References 40 · Cited by 156

Research works printed but not linked: 5

  1. Braunstein J, 1999, Peoples of the Gran Chaco
  2. Lanza N, 2009, Soc Biol Hum Aff, 73, 26
  3. Reyner LA, 1995, Sleep, 18, 127
  4. Wehr TA, 1993, Am J Physiol, 265, R846
  5. Worthman CM, 2009, Front Neurosci, 3, 1

Authors
de la Iglesia, H. O., Fernández-Duque, E., Golombek, D. A., Lanza, N., Duffy, J. F., Czeisler, C. A., & Valeggia, C. R.
Affiliations
  • Department of Biology, University of Washington, Seattle, Washington, USA
  • Department of Anthropology, Yale University, New Haven, Connecticut, USA
  • National University of Quilmes (AR)
  • Consejo Nacional de Investigaciones Científicas y Técnicas (AR)
  • Brigham and Women's Hospital (US)
  • Yale University (US)
Corresponding author
Valeggia, Claudia R.
ORCID
Venue
Journal of Biological Rhythms
Publisher
SAGE Publications
Published
2015-06-18
Volume
30
Issue
4
Pages
342-350
ISSN
  • 0748-7304 (ISSN-L)
  • 1552-4531
DOI
10.1177/0748730415590702
PMC
PMC5320422
OpenAlex
W2168194151
Semantic Scholar
e6a22f5332cc2078e57adefef0dcf1ef74068548
Cited by
156
References
40
Citations by year
2026: 10 · 2025: 10 · 2024: 3 · 2023: 14 · 2022: 18 · 2021: 20 · 2020: 18 · 2019: 16 · 2018: 12 · 2017: 14 · 2016: 18 · 2015: 3
FWCI
8.69
Type
journal article
Language
en
Open access
Licence
journals.sagepub.com/page/policies/text-and-data-mining-license (tdm)
Locations
  • Journal of Biological Rhythms (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
  • Conicet (submittedVersion, cc-by-nc-sa)
Funders
  • National Science Foundation (0909716, 0952264)
  • Universidad Nacional de Quilmes
  • Agencia Nacional de Promoción Científica y Tecnológica
  • National Heart, Lung, and Blood Institute (R01HL094654)
  • Division of Integrative Organismal Systems
Topics
  • Life Sciences › Neuroscience › Endocrine and Autonomic Systems › Circadian rhythm and melatonin
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and related disorders
  • Physical Sciences › Environmental Science › Global and Planetary Change › Impact of Light on Environment and Health
Keywords
artificial light at night, sleep duration, sleep onset, bedtime timing, sleep-wake cycle, hunter-gatherers, circadian rhythm, light pollution, indigenous peoples
MeSH terms
Adult, Argentina, Circadian Rhythm, Electricity, Female, Humans, Indians, South American, Light, Lighting, Male, Middle Aged, Seasons, Sleep, Time Factors, Wakefulness, Photoperiod, Young Adult

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-10.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-10.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

Are you an author, or do you see a problem with this page? Request a review