Effects of extreme air pollution and El Niño Southern Oscillation on insufficient sleep: a cross-sectional study

While there are many well understood clinical risk factors on sleep patterns, the associations of environmental factors, specifically air pollution on insufficient sleep remains understudied. This study investigates the association between insufficient sleep and particulate matter 2.5 (PM_2.5) among adults in the United States. There is also a need to determine whether various El Niño Southern Oscillation (ENSO) phases are effect modifiers in this relationship.

A cross-sectional observational analysis using annual survey data from 3100 United States counties for adult (≥ 18 years) age-adjusted insufficient sleep prevalence from 2017 to 2024. Annual average county-specific PM_2.5 data was categorized into three categories [low (< 5 µg/m³), moderate (5-11 µg/m³), extreme (≥ 11 µg/m³)]. The annual average ENSO index was used to determine if the year was either El Niño, La Niña, or neutral. Adjusted associations were conducted using Poisson regression and were stratified by various phases of ENSO. Adjusted associations were reported as rate ratio (RR).

From 2017 to 2024, the United States annual insufficient sleep is 34% [range min to max: 23-49%]. With respect to low PM_2.5; moderate and extreme PM_2.5 levels were associated with an increased risk of insufficient sleep by 1.03 (95% CI 1.02-1.05, P < 0.001) and 1.11 (95% CI 1.09-1.12, P < 0.001), respectively. The interaction between PM_2.5 and ENSO was significant (P < 0.001) on insufficient sleep. The magnitude in associations between extreme PM_2.5 and insufficient sleep differed by various ENSO phases.

Long-term (i.e. annual) effects of air pollution can pose a risk on adult sleep. While El Niño and La Niña phases were found to be a significant effect modifier, yet during the neutral phase the risks for extreme PM_2.5 were observed to be the strongest on insufficient sleep. Further investigations are needed to recognize the environmental effects on sleep deprivation.