CohortHumann = 15,581 men (10,670 in Denmark, 4,911 in Florida)2026
Seasonal trends in sperm quality in Denmark and Florida.
Plain-language summary
This study set out to see if sperm quality changes with the seasons in Denmark and Florida, and whether outdoor temperatures play a role. It looked at semen samples from 15,581 men aged 18, 45 who applied to be sperm donors, using computer-assisted analysis to measure sperm concentration and motility. The results showed that the concentration of fast-moving sperm peaked in warmer months (June-July) and dropped in colder months (December-January) in both countries, though total sperm concentration and ejaculate volume stayed steady. The findings suggest that sperm motility varies seasonally, even in warm climates, and that factors beyond temperature may be at play.
Key findings
- The concentration of fast-moving sperm was highest in warmer months (June-July) and lowest in colder months (December-January) in both Denmark and Florida.
- Total sperm concentration and ejaculate volume did not vary seasonally.
- Seasonal changes in sperm motility persisted even after accounting for outdoor temperatures.
How to analyze the study yourself
- Study type
- Cohort studies are good at tracking patterns over time but cannot prove what causes them.
- Population
- Men aged 18, 45 applying to be sperm donors in Denmark and Florida.
- Funding
- Not reported
- Watch for
- This study found that sperm motility peaks in warmer months and drops in colder ones, even in warm climates. If you are trying to conceive, it may be worth timing fertility efforts around these seasonal patterns.