Ambient temperature as the main driver of circannual variations in human semen quality in Southwest China

Male fertility decline and environmental deterioration are global concerns, but the link between rhythmic changes in male semen quality and environmental fluctuations remains unclear.

Using big data, this study identified monthly and seasonal variations in semen parameters among men in Chengdu and their associations with temperature, precipitation, and air pollution, aiming to aid clinical interpretation and pregnancy preparation guidance.

We analyzed semen parameters from 56,035 men in Chengdu during 2024. Participants were grouped by month and season to assess parameter differences and calculate abnormality rates. Environmental data (temperature, precipitation, AQI) were included. Partial correlation analysis and multiple linear regression were used to explore environmental links and the impact of extreme temperatures.

Semen parameters showed significant monthly and seasonal fluctuations. December exhibited higher quality (greater volume, concentration, total sperm, normal morphology, acrosome function; lower DNA fragmentation), while January showed poorer quality. Seasonally, spring had better progressive motility and survival rate; winter was worse. Temperatures of 26-29 °C (July-August) negatively affected viability (p = 0.023) but positively influenced morphology (p = 0.009). Routine parameters were more susceptible to extreme temperatures (coldest 2.5%: ≤4 °C; hottest 2.5%: ≥30 °C).

This study confirms that semen parameters exhibit circannual changes linked to temperature, precipitation, and AQI. These fluctuations should be considered in male fertility evaluation.