Identifying critical windows of apparent temperature exposure and male serum reproductive hormone levels

Although previous studies have suggested that environmental temperature may influence male reproductive hormone levels, evidence regarding the association between apparent temperature exposure and male reproductive hormones remains limited and inconsistent, and the potential susceptible exposure windows have not been clearly identified. Therefore, this study aimed to systematically identify the susceptible windows during which apparent temperature exposure affects male reproductive hormonal homeostasis. The analysis was based on the Anhui Prospective Assisted Reproductive Cohort, including a total of 3284 participants. Individual-level meteorological exposures were estimated based on data from meteorological monitoring stations, while air pollutant exposures were assessed using a validated machine learning model. Distributed lag nonlinear models (DLNMs) were applied to systematically identify potential susceptible windows within the 0-90 days preceding serum collection, after adjusting for relevant confounding factors. In addition, stratified analyses were performed to evaluate potential effect modification by smoking status. The results showed that exposure to apparent temperature was associated with alterations in male reproductive hormone levels, with potential susceptible exposure windows observed at several specific lag intervals within the 0-90 days exposure window. Lower apparent temperature exposure was associated with decreased levels of follicle-stimulating hormone (FSH) and estradiol (E₂), accompanied by an increased testosterone-to-estradiol ratio (T/E₂), whereas higher apparent temperature exposure was related to decreases in testosterone (T), E₂, and the testosterone-to-luteinizing hormone ratio (T/LH). Furthermore, these associations were more pronounced among non-smokers. These findings suggest that apparent temperature exposure may be associated with alterations in male reproductive hormone homeostasis.