Association between diurnal temperature range and sperm quality: Evidence from a prospective cohort in Central China

Inter-day temperature variability has been reported to be associated with sperm quality in a city-level exposure assessment study. However, studies exploring the impact of temperature variability within a single day on sperm quality at individual level are still lacking. The present study aims to bridge this research gap by analyzing the linear and non-linear associations between diurnal temperature range (DTR) exposure and sperm quality, utilizing data from the Anhui Prospective Assisted Reproduction Cohort. The study included 15,112 males (totaling 28,267 tests) and assessed individual exposure to various environmental factors (residential greenness, ambient particulate matter, sulfur dioxide, relative humidity, ambient temperature, and DTR) during the 0-90 day period before semen analysis. A combination of a linear mixed model, natural cubic splines, and subgroup analysis was employed. Significant "U"-shaped non-linear associations were observed between DTR exposure and total motility, sperm concentration, sperm count, total motile sperm count, and progressive motile sperm count. Lower DTR levels negatively impacted these parameters, whereas higher DTR levels showed a positive effect. Notably, these associations were more pronounced at ambient temperatures below 16.5 °C, while absent in warmer conditions. Sperm quality demonstrates increased sensitivity to DTR exposure in cooler environments. Therefore, implementing effective individual temperature management strategies is crucial for mitigating decreased sperm quality associated with DTR exposure, highlighting the potential benefits of government policies aimed at achieving carbon neutrality to enhance overall sperm quality in the general population.