Effects of Hot Night Exposure on Human Semen Quality: A Multicenter Population-Based Study.

Objective: To explore and quantify the association of hot night exposure during the sperm development period (0-90 lag days) with semen quality. Methods: A total of 6,640 male sperm donors from 6 human sperm banks in China during 2014-2020 were recruited in this multicenter study. Two indices (i.e., hot night excess [HNE] and hot night duration [HND]) were used to estimate the heat intensity and duration during nighttime. Linear mixed models were used to examine the association between hot nights and semen quality parameters. Results: : -0.0043, -0.0002), respectively. Consistent results were observed at different temperature thresholds on hot nights. Conclusion: Our findings highlight the need to mitigate nocturnal heat exposure during spermatogenesis to maintain optimal semen quality.