Sperm motility peaks in summer, study suggests

Researchers analyzed more than 15,000 semen samples from donor applicants collected in Denmark and Florida between 2018 and 2024 and found sperm motility was highest in June–July and lowest in December–January, while ejaculate volume and sperm concentration showed no clear seasonal change.

Researchers report seasonal variation in sperm motility based on donor samples from Denmark and Florida. Scientists affiliated with universities in the UK, Canada and Denmark analyzed more than 15,000 semen samples collected from 2018 to 2024 at Cryos International clinics. They measured ejaculate volume, sperm concentration and sperm motility across months of the year. The team found motility varied by season while volume and concentration did not. Key findings: - The analysis covered over 15,000 semen samples from men who applied to be sperm donors, collected between 2018 and 2024 at Cryos International clinics in Denmark and Florida. - Researchers assessed ejaculate volume, sperm concentration and sperm motility for each month of the year. - Sperm motility was highest in June and July and lowest in December and January in both northern Europe and southern U.S. locations. - Total sperm concentration and ejaculate volume did not show a clear seasonal pattern in the study. - The authors reported that ambient temperature alone is unlikely to explain the pattern and suggested factors such as daylight exposure or other environmental shifts may contribute; they also noted prior studies have sometimes reported different seasonal results and cautioned that sample sizes, methods or local climates can affect findings. Summary: The study indicates a seasonal pattern in sperm motility that is consistent across two different climates while concentration and volume remain stable. The researchers recommended that seasonality be considered when evaluating semen quality, and they noted further work is needed to explore underlying causes and implications for clinical practice.