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Sperm count, concentration and speed suffer under extreme heat, scientists warn

Sperm count, concentration and speed suffer under extreme heat, scientists warn

Sperm counts are at risk of dropping as the planet heats up, according to a team of scientists.

Reproductive cells are already known to be affected by heat, but the findings from researchers in Singapore give more detailed insights into how climate change could impact fertility rates.

Men who were exposed to extreme heat in the three months prior to providing a semen sample had a 46 per cent higher chance of a low sperm count, they found.

The risk of a low sperm concentration also shot up by 40 per cent, and the ‘little swimmers’ were notably more sluggish.

Dr Samuel Gunther, a research fellow at the Yong Loo Lin School of Medicine who was involved in the study, said young men in particular should take heed.

“Conventionally, findings suggest that sperm quality decreases as one ages, but what we found in this study was that it was men in their [prime] reproductive time between 25 and 35 who were the most impacted by heat,” he said during a media briefing.

“So just because you’re a young male, don’t think you’re invincible, and don’t think you’re not also vulnerable to these impacts,” Dr Gunther added. “Moving forward, the climate is going to get hotter. And that is also something that we need to bear in mind in family planning,”

How can men protect their sperm during heatwaves?

Semen samples were taken from 818 men in Singapore who had experienced issues conceiving.

The researchers tracked the men’s exposure to extreme heat - or when a day’s average temperature crossed 29.8C - by studying weather records 90 days before they provided the samples.

Men who are planning to conceive in one to three months should avoid going outdoors on extremely hot days, the researchers advised.

To boost their chances, they should also give saunas and hot baths a miss, as well as tight underwear. Sleeping in cooler environments is advisable too.

Singapore’s tropical climate - with year-round high temperatures and milder fluctuations - differs substantially to that of northern European countries, of course.

But Dr Gunther said the findings suggest that it might not take much temperature change to damage sperm health.

That doesn’t bode well given increased heat stress worldwide, and adds to the list of potential climate impacts on human health, from our hearts to kidneys. Previous studies have also looked at the link between air pollution and infertility.

Are women's eggs impacted by hotter temperatures too?

Extreme heat is also known to affect women’s ovulation cycle and egg quality.

The new Singaporean study is part of the National University of Singapore’s ‘HeatSafe’ programme, exploring the impact of extreme heat across society.

Tracking the birth records of more than 31,000 women, the researchers found a positive link between avoiding extreme heat during the third trimester of pregnancy and a lower risk of premature births.

Pregnant women tended to take more protective measures where they could, such as turning up the air conditioning.

Other HeatSafe projects focus on the welfare of construction workers and gig workers under sweltering conditions.

Possible solutions for the former include carrying insulated cool water, enforced breaks and breathable uniforms.