Warming testicles only slightly can lead to male infertility

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OKAZAKI, Japan — Colder is better when it comes to male fertility, a new study reveals. Researchers in Japan have found that even slight changes in the temperature of a man’s testicles can quickly result in a failure to produce healthy sperm.

Spermatogenesis is the process in which sperm cells develop within the testes of a male. The testes contain numerous thin and tightly coiled tubes, called the seminiferous tubules. Sperm cells develop within the walls of these tubules.

The new study found that at 34° Celsius (93.2° Fahrenheit), spermatogenesis is able to successfully produce healthy sperm. However, at temperatures between 37 and 38°C (98.6 and 100.4°F), this process severely breaks down.

Specifically, the process which segregates homologous chromosomes into haploid sperms (meiosis) begins to malfunction. Damaged cells also start to undergo cell death, leading to infertility.

temperature sperm
Blue bars indicate the germ cell types observed in testis explants cultured at the indicated temperatures. *No germ cells survived at 40°C. (CREDIT: NIBB)

Heat is bad for humans and animals

Researchers note that several previous studies have examined the link between heat and spermatogenesis impairment among animals. Those experiments involved relocating the testes to an animal’s abdomen, where body temperature is between 98.6 and 100.4°F.

However, those experiments could not control the actual testicular temperature. The new study used a testis organ culture to support complete spermatogenesis inside an incubator. By culturing mouse testes at different temps, the team discovered that spermatogenesis fails in several stages as temperatures rise from 30°C (86°F) to 40°C (104°F).

“We did not expect such a delicate ensemble of multiple temperature-dependent events to underpin this well-known phenomenon. This discovery could only have been achieved using an organ culture system,” says study leader Shosei Yoshida from the National Institute for Basic Biology in a media release.

In terms of meiosis dysfunction, the ability to repair DNA double-strand breaks and homologous chromosome pairing breaks down between 37 and 38°C. These two abilities are necessary for proper chromosome segregation.

sperm cell death
At 34°C (scrotal temperature), meiosis proceeds normally with all the homologous chromosomes paired normally. At 37 and 38°C (body core temperature), spermatocytes show aberrant chromosome pairing and undergo cell death. (CREDIT: NIBB)

“It was surprising that essential processes, such as meiosis, can be easily damaged at normal body core temperatures. Through the combined functions of the scrotum and checkpoint, only sperm developed at low temperatures fertilizes eggs to generate the next generation. Key questions for future studies include the molecular mechanism of heat sensitivity and the biological significance of low temperatures in sperm production,” concludes Kodai Hirano, the primary contributor to this study.

The findings appear in the journal Communications Biology.

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About the Author

Chris Melore

Chris Melore has been a writer, researcher, editor, and producer in the New York-area since 2006. He won a local Emmy award for his work in sports television in 2011.

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  1. IIRC, in the 1930s there was already a Doctor, in India, showing that testicular heating in human males was a useful form of birth control, at around 105ºF. With as little as 1 hour a day heating, for 2 weeks, using a water bath, she was able to produce infertility that lasted as much as 6 months. However, there seemed then, and now, little enthusiasm for her work.

    When I have described it at social gatherings the major objection has been that the woman was not in charge of fertility, and would not trust the male. Perhaps it would be useful for married couples who both acknowledge they have as many children as they want? Here is a wiki-discussion of the topic.


    1. I just bake mine in an oven set on broil for 10 minutes twice a day.

      Produces the same effect.

  2. Putting it bluntly, a man who deliberately defeats his own fertility makes himself less a man.

    A man has the potency God and nature gave him, and through self-mastery knows when and when not to use it: and acts accordingly. Don’t want to have a child at this time? Be a man: don’t copulate.

    True freedom does not come from indulging every whim and desire. It comes from choosing or abstaining from actions freely, at the right times, for the good of others and yourself.

    Sterilizing yourself shows you don’t trust your ability to handle true freedom like a mature, responsible adult.

  3. Looks like grant money grifter science. Every livestock breeder knows this. Why was time, money, and effort was spent on this study?

    1. Yepdecades ago we learned that jockey shorts caused male infertility..looks like some pseudo-science here. And it ties into the new religion of “Global Warming”! Bill gates will be thrilled-another way to limit the human [population. Complete dreck.

  4. That must be why birth rates in countries with cold climates are so much higher than those in warm climates. Oh, wait…

  5. If that’s true, then why do Indians and Africans reproduce so much?

    1. Because they are cool while Whites are always boring at parties and never get the chicks.

  6. There ain’t no such thing as Testicle warming. It’s all a scam by testicle cooler makers to put the holy Jock Strap makers out of business, steal your money, and bring America to communism through the establishment of a one world government run by the U.N. and George Soros.

  7. Testicles near body core temperature a bad thing. Like momentary Jockstrap use. Like 24/7 tight circumcision.

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