Synergistic and antagonistic interactions of PM2.5 with high and low temperatures on sperm motility: Evidence from a prospective cohort study.

Given that temperature and fine particulate matter (PM2.5) may jointly influence semen quality through overlapping biological pathways, including oxidative stress, inflammation, and endocrine disruption, while epidemiological evidence regarding their interaction remains limited, we conducted this study to evaluate their associations and potential interactions. We applied linear mixed models (LMMs) with natural cubic splines to characterize potential nonlinear associations between temperature and semen quality. To further examine whether these associations differed by PM2.5 exposure levels, we conducted stratified piecewise regression analyses of temperature separately within the higher and lower PM2.5 exposure groups across the low- and high-temperature segments. Temperature showed inverted U-shaped associations with semen quality during the 0-90, 0-9, 10-14 day exposure windows. Further stratified piecewise regression analyses suggested a synergistic interaction between high temperature and PM2.5 and an antagonistic interaction between low temperature and PM2.5, mainly affecting progressive motility and total motility. Our findings suggest that PM2.5 may modify the association between temperature exposure and sperm quality, particularly progressive motility and total motility, and that the combined effect of high temperature and PM2.5 warrants further attention in male reproductive health research and prevention.