Short-term exposure of non-optimal temperature and lung function: The role of relative humidity

Although ambient temperatures are expected to increase, the association of temperature and small airways has not been reported. Additionally, the results for temperature and large airway function remain inconsistent, possibly due to insufficient consideration of the modifying role of relative humidity. This study aimed to quantify the effects of temperature on both large- and small-airway function, and the interactive effects of relative humidity on lung function.

Pulmonary function results were obtained from a national cross-sectional study, the China Pulmonary Health Study (N = 42,805). Generalized linear models and generalized additive models were used to examine the associations between temperature and eight lung function indicators. We further investigated the interactive effects of non-optimal temperatures and relative humidity on lung function.

All lung functions consistently exhibited inverse J-shaped exposure-response relationships. Compared to the moderate temperature, both low and high temperatures were significantly associated with decreased lung function. Participants exposed to both low temperature and low relative humidity had more pronounced changes in FEV₁ (-90.34 ml; 95 % confidence interval [CI]: -113.35, -68.52), FVC (-93.23 ml; 95 %CI: -118.72, -67.73), FEV₃ (-100.53 ml; 95 %CI: -125.30, -75.76), FEF_25-75 (-165.56 ml/s; 95 %CI: -204.98, -126.14) and other lung functions than did those in the moderate temperature and high relative humidity group.

Compared to the large-airway function, the small-airway function is more vulnerable to non-optimal temperatures, with more pronounced reductions under both low temperatures and low relative humidity. Targeted adaptive strategies and measures are needed to mitigate the adverse effects of temperature-humidity on lung function under climate change scenarios.