Heat stress in relation to sleep health among farmers: a cross-sectional study

Heat exposure has been linked to sleep disturbances in the general population, but farmers, who are particularly vulnerable due to outdoor occupational exposures-have been rarely studied in this context. this study aimed to investigate associations between heat stress and sleep health among farmers.

We conducted cross-sectional analyses of 8,203 male farmers from Iowa (78%) and North Carolina (NC, 22%) in the Agricultural Health Study (2013-2015). Daily wet bulb globe temperatures (WBGT) from May 2013-September 2015 was used. We calculated absolute heat stress by averaging WBGT over 2/5/7 days before the interview. Relative heat stress (i.e., the difference between absolute heat stress and the 92.5th percentile of WBGT) was also calculated. WBGT was categorized by heat stress risk (low, moderate, high). Sleep outcomes included short sleep (< 7 h), daytime sleepiness (≥ 3 days/week), napping (yes), and long naps (≥ 30 min). Poisson regression with robust variance estimated adjusted prevalence ratios (PRs) and 95% confidence intervals (CIs), stratified by state.

Farmers averaged 63 years old (SD = 10.1); 37.8% reported short sleep, 8.1% daytime sleepiness, 44.6% napping, and 17.1% long naps. Mean absolute WBGT were 70.4 °F (SD = 6.36) in Iowa and 77.7 °F (SD = 7.83) in NC. In Iowa, moderate heat stress (2-day average) was associated with higher short sleep prevalence (PR = 1.04 [1.00-1.07]). In NC, higher absolute (2-/5-/7-day average) and relative WBGT (2-day average), as well as moderate (2-/7-day) and high (2-day) heat stress were associated with daytime napping (e.g., PR _{2-day absolute WBGT}= 1.02 [1.01-1.04]). In both states, high heat stress was linked to lower prevalence of long naps (e.g., PR_{Iowa, 2-day heat stress}= 0.86 [0.83-0.89]).

Heat stress was associated with a small/weak but potentially meaningful relationship with poor self-reported sleep among farmers. Future studies using objective sleep measures are needed. Although our findings highlight the potential importance of incorporating heat mitigation and sleep health strategies into occupational safety guidelines for agricultural workers, the cross-sectional design of this study precludes causal conclusions.