A study suggests that the quality of human sperm peaks in the summer, although some experts have raised doubts.
Human sperm quality is evaluated based on the level and concentration of 'forward-moving sperm,' which are capable of swimming in a straight line and efficiently. Analysis of semen samples has revealed that this 'sperm quality' fluctuates seasonally, potentially peaking in the summer.
Seasonal trends in sperm quality in Denmark and Florida | Reproductive Biology and Endocrinology | Springer Nature Link
Sperm quality may change with the seasons, study finds | Live Science
https://www.livescience.com/health/reproductive-health/sperm-quality-is-at-its-peak-in-the-summer-study-finds
A study published in the academic journal *Reproductive Biology and Endocrinology* involved medical and biologists from Cryos International , a sperm and egg bank in Denmark, the University of Manchester in the UK, and Queen's University in Canada, who analyzed semen samples. To investigate changes in sperm quality over time, semen samples were analyzed from 15,581 men aged 18 to 45 who consented to sperm donation between 2018 and 2024. Samples were collected in four cities in Denmark and Orlando, Florida.
Furthermore, computer-assisted sperm analysis was used to measure the semen volume, sperm concentration, and the amount of 'progressively motile sperm'—sperm capable of swimming in a straight line—in each sample, which are considered particularly important indicators in fertilization.
The researchers reported that their analysis revealed a clear seasonal pattern in the concentration of highly motile sperm, peaking in June-July and peaking in December-January.
While it is known that semen quality changes with temperature, this study found no evidence that the temperature at the time of ejaculation directly affects sperm quality. Furthermore, since sperm develop in the body over approximately 74 days, the study also investigated whether the temperature in the weeks prior to ejaculation affects sperm quality. Similar to the temperature at the time of ejaculation, there was little evidence of a measurable correlation between the temperature two months prior to ejaculation and sperm quality. Therefore, it is believed that season and temperature have an indirect influence on sperm quality.
Alan Pacey, a co-author of the paper and professor of men's studies at the University of Manchester, explained, 'Even after accounting for temperature changes, seasonality still existed, suggesting that other lifestyle changes may be important. These could include diet, exercise, and sun exposure. However, since we did not measure these factors, we can only speculate.'
Pacey also stated, based on the analysis, 'These measurements suggest that men may have a higher chance of being accepted as sperm donors if they apply in the summer. Furthermore, couples hoping to have a baby in Denmark or Florida may also have better luck applying in the summer. However, it's important to note that this is only a hypothesis.'
On the other hand, Dr. Sherman Silver, a urologist and director of a fertility center in St. Louis, reviewed the study and pointed out that 'seasonal variations in sperm motility are unlikely to affect actual conception.' According to Dr. Silver, seasonal changes in sperm quality may be a remnant of evolution, as many animals in temperate climates have adapted to breed in the spring. However, in the case of humans, this seasonal influence may be weaker because we have adapted to survive well into winter.
In an email to the science media outlet Live Science, Silver stated, 'The difference reported in this study is 'very small,' to the point where it can be said that there is no biological difference at all.'
Furthermore, while past studies have shown trends consistent with the findings of this study, a 2021 study by a Chinese research team that analyzed more than 20,000 semen samples showed the opposite result: 'Sperm motility peaks at the end of winter and declines during the summer.' The authors of this study state that these differences in research results suggest that regional lifestyle and environmental factors, such as differences in temperature, humidity, and social behavior, may be influencing the temporal fluctuations in sperm quality.
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