The association between ambient temperature and semen quality in a Northern Peninsular Province, China.

Background: Extreme ambient temperature has been linked to decline in males' semen quality. Although the temperature-semen quality association has been examined in certain cities of South China, how the effect size of the extreme temperature may lag over critical windows in spermatogenesis and whether the strength of association may vary in North China have yet been adequately explored.

Objectives: To quantify the association between air temperature and semen quality, and identify critical exposure windows in a Northern Peninsular Province, China.

Materials and methods: Data on semen quality in 2014-2019 were collected from the Human Sperm Bank of Institute of Women, Children and Reproductive Health, Shandong University, China. Daily meteorological data (0.01°×0.01°) were assigned to each subject's residential address. The linear mixed-effect model combined with the distributed lag nonlinear model was used to estimate the effect of ambient temperature over critical spermatogenesis windows.

Results: The temperature-semen quality association was inverted V-shaped, with the maximum lag being 0-45 days before ejaculation and the threshold being 9.2°C. Progressively and total motile sperm number, and total sperm number declined more substantially than other semen quality parameters. Semen quality was more sensitive to cold exposure during the epididymal storage period than the sperm motility development period. By contrast, semen quality was insensitive to heat exposure during both critical spermatogenesis windows. Impairment of certain semen quality parameters was more obvious for males with higher educational attainment and those aged over 35 years.

Discussion and conclusion: Exposure to non-optimal temperature is associated with decreased semen quality in North China, with the epididymal storage and sperm motility development periods more sensitive to cold exposure than heat. Older males and those with higher educations may need particular awareness.