Seasonal changes in behavior — but not temperature — can subtly influence sperm motility. However, it is not certain that this variation in sperm quality influences fertility.
A new study, recently in Reproductive Biology and Endocrinologysuggests that sperm quality human follows a seasonal pattern, reaching the peak in summer and descending in winter.
As detailed by Live Science, the research analyzed semen samples from more than 15,000 sperm donors in Denmark and the USA, specifically in the state of Florida.
In both populations, scientists found a consistent pattern: higher levels of progressively motile sperm — sperm that can swim efficiently in a straight line — appeared in June and July.
On the contrary, the lowest levels occurred in December and January.
To explore sperm quality over time, researchers analyzed semen samples from 15,581 men aged 18 to 45 who applied to be sperm donors between 2018 and 2024. Samples were collected in four Danish cities — Aarhus, Aalborg, Odense and Copenhagen — as well as Orlando, Florida.
The team used computer-assisted sperm analysis to measure semen volume, sperm concentration, and the number of progressively motile sperm in each sample.
As Live Science points out, progressively motile sperm swim in straight lines or large circles, while non-progressively motile sperm move in tight circles but don’t move forward.
Not so much, research does not conclude that this variation on sperm quality influence fertility.
In fact, Sherman Silberurologist and director of The Silber Infertility Center de St. Louiswho was not involved in the study, refers to the aforementioned magazine that he thinks the seasonal variation in sperm motility is unlikely to affect fertility in the real world.
“The differences reported in this study are very, very small and make absolutely no difference from a biological point of view”, he points out.
Because sperm take about 74 days to develop in the body, the researchers also examined whether temperatures in the weeks leading up to ejaculation could influence sperm quality.
However, found little evidence that either temperatures at the time of ejaculation as those two months earlier had any measurable connection with sperm quality.
Still, the temperature can indirectly influence sperm quality by influencing lifestyle factors known to affect sperm quality, the researchers hypothesized.
“This may include diet, exercise, exposure to sunlight”, he listed Allan Paceyprofessor of andrology at the University of Manchester, who was part of the Live Science study.
Silber, in turn, thinks that the seasonal pattern could be a evolutionary trace.
In many animals that live in temperate climates, reproduction is synchronized so that offspring are born in spring, when conditions are more favorable and resources are more abundant.
If sperm quality peaks in the summer, this synchronization could increase the likelihood of spring births. In humans, however, this seasonal effect is probably attenuated, since humans have adapted to survive well in winter – proposes Silber.
