Hot Nights, Sleepy Days: An investigation into Ambient Temperature and Daytime Sleepiness - A cross-sectional study in adults in Johannesburg, South Africa (2017-2018)
1
HE²AT Center, Wits Planetary Health Research, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
2
SAMRC/Wits Developmental Pathways for Health Research Unit, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
3
Biomedical Research and Innovation Platform, South African Medical Research Council, Cape Town, South Africa
Popul. Med. 2026;8(Supplement Supplement 1):A434
ABSTRACT
BACKGROUND:
Excessive daytime sleepiness is an indicator of sleep disorders and disruptions1. Heat exposure can impair sleep onset and quality through thermoregulatory disruption2,3, as the core body temperature must decrease for sleep initiation and maintenance2,4,5. Poor sleep quality and disturbances are associated with increased daytime sleepiness, impaired cognitive function, mood disorders, increased occupational risks and car accidents1,6. Heat-induced sleep disruptions are recognised as a pathway linking climate change to human health7. The aim was to investigate the association between ambient temperature and excessive daytime sleepiness in middle-aged Johannesburg adults.
METHODS:
Data from the Middle-Aged Soweto Cohort (MASC), collected 2017-2018, were analysed. Participants (N=993) completed the Epworth Sleepiness Score (ESS; 0-24), a validated questionnaire measuring daytime sleepiness (higher ESS = increased sleepiness)1,8. ERA5 global climate dataset (from the European Centre for Medium-Range Weather Forecasts) was linked to individual clinic visits by date. Outcomes included continuous ESS and binary excessive daytime sleepiness (ESS >10, a clinical threshold). Logistic and linear regression models adjusted for age, sex, BMI, and HIV status.
RESULTS:
Of 993 participants, 155 (15.6%) had excessive daytime sleepiness. Per 5°C temperature increase, ESS increased by 0.65 points (95% CI: 0.29, 1.01; p<0.001), indicating increased daytime sleepiness with increasing ambient heat. For each 5°C increase, odds of excessive daytime sleepiness increased by 57% (OR=1.57; 95% CI: 1.26, 1.97; p<0.001). Temperature was significantly associated with ESS; age, sex, BMI, and HIV status showed no independent associations with ESS.
CONCLUSIONS:
Higher ambient temperature is significantly associated with daytime sleepiness in Johannesburg adults, with a 57% increased odds of excessive sleepiness per 5°C increase in temperature. As high temperatures interfere with the physiological temperature drop required for sleep onset and maintenance, heat-induced sleep disturbance represents a plausible mechanistic pathway linking climate to health outcomes. These findings support integrating sleep health into heat adaptation strategies.
Excessive daytime sleepiness is an indicator of sleep disorders and disruptions1. Heat exposure can impair sleep onset and quality through thermoregulatory disruption2,3, as the core body temperature must decrease for sleep initiation and maintenance2,4,5. Poor sleep quality and disturbances are associated with increased daytime sleepiness, impaired cognitive function, mood disorders, increased occupational risks and car accidents1,6. Heat-induced sleep disruptions are recognised as a pathway linking climate change to human health7. The aim was to investigate the association between ambient temperature and excessive daytime sleepiness in middle-aged Johannesburg adults.
METHODS:
Data from the Middle-Aged Soweto Cohort (MASC), collected 2017-2018, were analysed. Participants (N=993) completed the Epworth Sleepiness Score (ESS; 0-24), a validated questionnaire measuring daytime sleepiness (higher ESS = increased sleepiness)1,8. ERA5 global climate dataset (from the European Centre for Medium-Range Weather Forecasts) was linked to individual clinic visits by date. Outcomes included continuous ESS and binary excessive daytime sleepiness (ESS >10, a clinical threshold). Logistic and linear regression models adjusted for age, sex, BMI, and HIV status.
RESULTS:
Of 993 participants, 155 (15.6%) had excessive daytime sleepiness. Per 5°C temperature increase, ESS increased by 0.65 points (95% CI: 0.29, 1.01; p<0.001), indicating increased daytime sleepiness with increasing ambient heat. For each 5°C increase, odds of excessive daytime sleepiness increased by 57% (OR=1.57; 95% CI: 1.26, 1.97; p<0.001). Temperature was significantly associated with ESS; age, sex, BMI, and HIV status showed no independent associations with ESS.
CONCLUSIONS:
Higher ambient temperature is significantly associated with daytime sleepiness in Johannesburg adults, with a 57% increased odds of excessive sleepiness per 5°C increase in temperature. As high temperatures interfere with the physiological temperature drop required for sleep onset and maintenance, heat-induced sleep disturbance represents a plausible mechanistic pathway linking climate to health outcomes. These findings support integrating sleep health into heat adaptation strategies.
| eISSN: | 2654-1459 |
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