The influence of temperature and seasons on sperm quality: heat reduces male fertility

The influence of seasons on male fertility:
How does summer harm sperm?

If you're planning a pregnancy, you may be tracking ovulation, taking supplements, or making dietary changes. But there's one factor you probably haven't considered: the time of year can affect sperm quality .

Two studies (one from the US and the other from India) have shown that male fertility fluctuates depending on the season. And the results are clear: high temperatures reduce sperm quality .

Winter: a natural "boost" for men

In a large-scale study by Massachusetts General Hospital, more than 550 sperm samples were analyzed over an 11-year period. The results:

• Sperm concentration was highest in winter (157.9 million/mL) and lowest in autumn (119.1 million/mL).
• Morphology (percentage of sperm with normal shape) was best in winter (9.2%) and worst in summer (7.0%) and spring (7.5%).
• Defects in the sperm head were more common in summer and autumn than in winter.

Researchers believe that cooler weather allows for optimal testicular temperature , which is crucial for sperm production. Spermatogenesis requires a temperature that is 2–3°C lower than body temperature. Even a small increase can be harmful, and the effects often take several months to show.

Average values of seed parameters by season (Chen et al., 2003)

Note: The highlighted numbers are the best values (in winter), while the underlined numbers are those that were statistically worse than the winter values (P < 0.05).

Even in tropical climates, there are seasons

In the Indian state of Kerala, where there are no large temperature fluctuations, more than 2,300 sperm samples were analyzed. Despite the tropical climate, seasonal differences were observed:

• Defects in the head and tail of sperm were most common in the summer , and least common in the rainy season.
• Sperm concentration was not statistically different between seasons, but it did drop noticeably in the summer .

In the summer, men were also found to have more white blood cells in their semen , which may indicate inflammation or stress in the reproductive tract.

What is causing these changes?

Researchers mention several possible explanations for why the deterioration occurs in the summer:

• Higher outside temperatures raise the temperature of the testicles, which is detrimental to sperm production.
• Photoperiod (day length) affects hormones such as melatonin and gonadotropins.
• Changes in activity, clothing, pollution, or infections can also affect sperm quality.

Spermatogenesis apparently follows a biological "calendar" coordinated with the environment.

What this means for couples wanting a child

If you're dealing with male infertility or low sperm count (oligospermia), choosing the right time of year for testing or treatment can affect the results:

• It is recommended to perform testing and procedures in winter or colder months .
• If the spermogram is poor in the summer, repeat it in the winter .
• Avoid additional heating of the testicles in the summer: do not wear tight underwear, do not use a laptop on your lap, avoid saunas and hot baths.

Finally

Yes, sperm quality is seasonal. In both cold and tropical climates, research shows that colder months have a beneficial effect on spermatogenesis, while heat impairs sperm concentration, motility, and shape.

So the next time you're thinking about the ideal time to conceive, don't just look at ovulation – consider the time of year too.

Sources:
Chen Z. et al. (2003). Seasonal Variation and Age-Related Changes in Human Semen Parameters , Journal of Andrology.
Malathi A. et al. (2023). Impact of Seasonal Variations on Semen Parameters , Journal of Human Reproductive Sciences.