The association between greenspace exposure and sperm quality: A retrospective cohort study focusing on sperm kinematics and the influence of buffer settings.

Background: While previous studies have suggested a potential link between greenspace and semen quality, the effect of greenspace exposure on sperm kinematics, as well as the impact of greenspace estimation scales, remains underexplored.

Objectives: This study aimed to examine the association between greenspace exposure and sperm kinematics, and to determine whether this relationship varies across different greenspace estimation scales.

Methods: We conducted a retrospective longitudinal study of 5025 semen measurements from 1674 sperm donors recruited by the Sichuan Provincial Human Sperm Bank (SHSB) between June 2019 and December 2021. Greenspace exposure was estimated using the Normalized Difference Vegetation Index (NDVI) for four buffer zones (250 m, 500 m, 1,000 m, and 2000 m) centred on the geocoded residential addresses. Linear mixed-effects models and restricted cubic spline models (knots = 4) were used to assess the associations between greenspace exposure and both conventional semen parameters and sperm kinematic parameters across all buffer zones.

Results: A non-linear association between NDVI-500m and progressive motility was observed for conventional semen parameters (P non-linear = 0.018). For sperm kinematics, NDVI-500m could be associated with multiple kinematic measures (VCL: % change = 1.81, 95% CI: 0.72, 2.91; VAP: % change = 2.57, 95% CI: 1.46, 3.70; VSL: % change = 3.37, 95% CI: 2.11, 4.66; LIN: % change = 1.51, 95% CI: 0.82, 2.21; STR: % change = 0.83, 95% CI: 0.44, 1.23; WOB: % change = 0.69, 95% CI: 0.35, 1.04; BCF: % change = 1.82, 95% CI: 0.97, 2.68), and significant non-linear associations were found between NDVI-500m and LIN (P non-linear = 0.011), STR (P non-linear = 0.015), WOB (P non-linear = 0.012), and ALH (P non-linear <0.001). Regarding the impact of greenspace estimation scales, smaller buffer zones exhibited stronger non-linear relationships for conventional semen parameters, whereas larger buffer zones revealed more pronounced non-linear relationships for sperm kinematics. There was a stable and significant linear association between greenspace exposure and sperm kinematics during the 70-90 days before ejaculation (spermatocytogenesis). PM and PM attenuated the negative effect of greenspace exposure on IM at a buffer scale of 250 m, while enhanced the positive effect of greenspace on kinematics at all scales.

Conclusions: Greenspace exposure were significantly associated with sperm kinematics, with the strength and nature of these associations varying by buffer scale. 70-90 days before ejaculation (spermatocytogenesis) was the window of susceptibility for greenspace exposures at all buffer scales. As PM and PM increased, increasing levels of greenspace can improve sperm kinematics more significantly. These findings support the beneficial effect of greenspace on male fertility, and underscore the importance of considering greenspace buffer zones in urban planning to optimize health benefits effectively.