Association between ambient temperature and semen quality among sperm donation volunteers in South China

Potential adverse effects of non-optimum temperatures on human semen quality have drawn much concern worldwide; however, the exposure-response relationship remains less understood.

To quantitatively assess the association between exposure to ambient temperature and semen quality in South China, and to identify potential critical exposure windows.

We conducted a longitudinal study to investigate 11,050 volunteers who lived in Guangdong province, China and intended to donate sperm in the Guangdong provincial human sperm bank during 2016-2021. Exposure to ambient temperature during 0-90 days before semen collection was assessed by extracting daily temperatures from a validated grid dataset at each subject's residential address. Linear mixed models and linear regression models were used to perform exposure-response analyses.

During the study period, the 11,050 subjects underwent 44,564 semen analyses. Each 5 °C increase of lag 0-90 day exposure to ambient temperature was approximately linearly associated with a 3.11 (95 % confidence interval [CI]: 2.08, 4.14) × 10⁶/ml, 9.31 (4.83, 13.80) × 10⁶, 1.27 % (0.91 %, 1.62 %), 8.20 (5.33, 11.08) × 10⁶, 1.37 % (1.01 %, 1.74 %), 8.29 (5.52, 11.06) × 10⁶, 0.67 % (0.28 %, 1.05 %), and 4.50 (2.20, 6.80) × 10⁶ reduction in sperm concentration, total sperm number, total motility, total motile sperm number, progressive motility, total progressive sperm number, normal forms, and total normal form sperm number, respectively (all p < 0.001), which was not significantly modified by age (all p for effect modification > 0.05). We identified a critical exposure period of 10-14 days before semen collection for sperm motility, and 70-90 days before semen collection for sperm count and morphology.

Our study provides consistent evidence that higher ambient temperature was significantly associated with a reduction in semen quality in South China. The findings highlight the needs to reduce high temperature exposures during 3 months before ejaculation to maintain better semen quality.