Ambient Ultraviolet Radiation and Human Semen Quality

Abstract Semen quality has declined globally, and limited evidence links longer sunlight duration to poorer semen quality. As one of the biologically active components of solar radiation, the impact of ultraviolet (UV) radiation on semen quality remains unclear. We aimed to examine the associations between ambient UV radiation and semen quality and identify potential windows of susceptibility. This longitudinal study included 16,349 sperm donation volunteers from Guangdong, China, during 2016–2024. Individual ambient UV radiation exposure was estimated using a daily gridded data set based on residential addresses. Associations between ambient UV radiation and semen quality were assessed using linear mixed models and linear regression models. Each interquartile range increase in ambient UV radiation exposure was associated with a decrease of 3.78 × 106/mL in sperm concentration, 11.43 × 106 in total sperm number, 1.04% in progressive motility, 0.96% in total motility, 9.53 × 106 in total progressive motile sperm number, and 9.59 × 106 in total motile sperm number at lag 0–90 day. Nonlinear associations for sperm motility and count were observed, generally characterized by an initial decline followed by attenuation or a slight upward trend at higher exposure levels. We identified lag 0–9, 15–69, and 70–90 day as critical windows for sperm count, and lag 0–9, 10–14, and 15–69 day as critical for sperm motility. No effect modification by age was observed. This study provides evidence that UV radiation may adversely affect semen quality and underscores the need to limit UV radiation exposure for those planning conceptions.