Khaberni - A new study has revealed that the quality of human sperm undergoes clear seasonal changes, where it is at its best during the summer months and its lowest in winter.
The researchers analyzed samples from more than 15,000 sperm donors in Denmark and the state of Florida, USA, and found a consistent pattern in both countries: the peak of sperm quality appeared in June and July, while the lowest levels were recorded in December and January.
This result has led scientists to wonder whether men who apply to donate sperm in the summer might have a better chance of being accepted, and whether couples trying to conceive might achieve more success in the same season. However, the researchers stress that this is just a theory that needs proving.
Dr. Sherman Silber, a urologist not involved in the study, believes that these seasonal variances are biologically very small and practically do not affect the chances of conception in real life.
When the researchers tried to explain why sperm quality rises in the summer and falls in the winter, they first tested the most obvious idea: temperature. Since sperm formation takes about 74 days, they examined the impact of temperature during the weeks leading up to ejaculation, but the results were surprising, as they found no clear relationship between temperature and sperm quality.
This means that the secret does not lie solely in temperature. Thus, the researchers moved on to another explanation, which is that lifestyle factors might be the real influencers, such as the quality of food a man eats, how much exercise he gets, and the degree of exposure to sunlight.
However, the researchers reached an important point here, as they did not directly measure these factors in their study, so they cannot definitively claim them as the cause, and it remains just a prevailing belief.
In contrast to this lifestyle-related explanation, Dr. Silber presents a different explanation entirely, one that is deeper and rooted in the evolutionary history of humans.
Silber believes that this seasonal pattern is not a product of the modern age, but rather "evolutionary remnants" from our distant ancestors.
However, he adds an important warning: this evolutionary effect is no longer strong in contemporary humans as in animals, because humans have adapted to living in all seasons, learning to provide food and warmth even in the harshest winter conditions, thus this "legacy" from our ancestors has become so weak today that it does not realistically affect the chances of reproduction.
This is not the first time that seasonal variations in sperm quality have been observed, but the previous results were conflicting. Some studies, like an Italian study, found a peak in sperm motility in the summer, just like the new study. Whereas other studies, such as a large analysis of more than 21,000 samples from southern China, found that the peak occurs in late winter and declines during the summer.
The researchers believe that regional differences in climate, humidity, and social behaviors might explain these contradictions.
In addition to seasonal change, the study found that a man's age plays an important role, where sperm motility was at its highest levels in men in their thirties, and lower among those under 25 years and over 40 years.
The researchers also noted a noticeable decrease in sperm quality in Denmark between 2019 and 2022, followed by a recovery in 2023, which may reflect the impacts of the COVID-19 pandemic and the associated lockdowns on work patterns, diet, and physical activity. On the other hand, Florida witnessed a gradual increase in sperm quality from 2018 to 2024, a trend that is still unclear and requires further research.
