Sperm swim more quickly in summer, study finds
BBC World
February 25, 2026
AI-Generated Deep Dive Summary
A new study reveals that sperm motility—its ability to swim effectively—is highest during the summer months, with June and July showing peak performance. Researchers analyzed semen samples from over 15,000 men in Denmark and Florida, finding consistent patterns regardless of climate. While sperm concentration and ejaculate volume remained stable throughout the year, motility levels fluctuated significantly, peaking in summer and reaching lows in winter months like December and January. This discovery underscores the importance of seasonal variations in male fertility.
The study, published in *Reproductive Biology and Endocrinology*, highlights how these patterns could be harnessed to optimize fertility treatments. By aligning treatment timing with optimal seasons, couples struggling with conception might see improved outcomes. Lead author Professor Allan Pacey noted the striking similarity in seasonal trends across vastly different climates, suggesting that factors beyond temperature—such as light cycles or hormonal changes—are at play.
Interestingly, sperm concentration and ejaculate volume showed no seasonal variation, indicating that motility is influenced by external factors rather than overall sperm production. The study also revealed that testicular temperatures need to remain slightly lower than body temperature for optimal sperm function. This
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Originally published on BBC World on 2/25/2026