Sperm quality is highest in the summer and lowest in the winter, according to a new study.
Researchers from the UK, Canada and Denmark analysed semen samples from 15,581 men in Denmark and Florida, all aged between 18 and 45.
Their findings show that sperm motility – the ability of sperm to swim effectively – was consistently highest in June and July for both parts of the world.
Understanding these seasonal patterns could improve fertility treatments, by optimising the timing of treatment and fertility testing to provide better guidance to couples trying to conceive.
The study, published in the journal Reproductive Biology and Endocrinology, suggests that sperm’s motility levels remain consistent across different climates, instead changing with the seasons.
Levels were lowest in December and January, even though Florida remains warm all year round.
But scientists found no changes in the total sperm concentration – the amount of sperm in someone’s semen – or the ejaculate volume, how much semen is ejected during ejaculation, no matter the season.
This means that while sperm’s ability to move effectively does vary by season, the time of year doesn’t impact the number of sperm produced.
These findings suggest that seasonal patterns may affect male fertility more than just temperature differences alone.
On average, the optimal temperature of the testes – where sperm is stored – should be two to four degrees lower than the average body temperature of 37 degrees.
Anything higher or lower than this can negatively affect sperm motility, therefore impacting fertility.
The University of Manchester’s Professor Allan Pacey, who co-authored the study, said: « We were struck by how similar the seasonal pattern was in two completely different climates.
« Even in Florida, where temperatures stay warm, sperm motility still peaked in summer and dipped in winter, which tells us that ambient temperature alone is unlikely to explain these changes. »
He added: « Our study highlights the importance of considering seasonality when evaluating semen quality. It also shows that seasonal variation in sperm motility occurs even in warm climates. These findings deepen our understanding of male reproductive health and may help improve fertility outcomes. »
