These findings could be crucial not only for couples longing for a family but also for reproductive medicine clinics and their interpretation of tests.
An international team of researchers from Denmark, the UK, and Canada analyzed over 15,000 sperm samples from donors in Denmark and the United States, reports EuroNews. The results showed clear seasonal changes in sperm quality.
The scientists focused on the concentration of so-called progressively motile sperm, which can effectively swim forward and have the highest chance of successfully fertilizing an egg. Data revealed that the concentration of these "fastest swimmers" starts to rise in spring, peaks at the beginning of summer, and then decreases to its lowest values in the middle of winter.
These differences don't mean that men are only fertile in summer and infertile in winter. Interestingly, the actual sperm production doesn't change throughout the year. The total number of sperm and the volume of ejaculate remain stable across all seasons. What varies is solely the quality and efficiency of their movement.
These findings provide important context for practice, as sperm analysis results in summer might differ from winter tests. While science has long known that sperm development is sensitive to temperature, previous smaller studies have yielded mixed conclusions, often suggesting that sperm fare better in cooler months.
