Study: boxer shorts improve fertility in men

Geschatte leestijd: 6 minuten Last week, research showed that boxers contribute to better fertility in men than briefs. This is due to the temperature difference of the testicles. Why should these actually be air-cooled? And what does it mean for testosterone?

Below the Belt

Ever wondered why a man’s testicles hang in a pouch outside the body? Testicles are glands, organs that produce and/or transport substances. In this case, testosterone. Testicles are also gonads, meaning they form reproductive cells. Quite important functions that make your existence as a man and reproduction possible. In a fetus, these are still protected in the abdominal cavity until about the ninth month of development. Then they ‘descend’ into the external scrotum. Men in MMA can smash each other’s heads to pulp. However, a misplaced hit to the balls can be a reason to give a fighter 5 minutes to recover. It’s quite ironic that what makes a man a man is also his weakest spot. Couldn’t that package be neatly tucked away in the abdomen? However, there is a reason for hanging that vulnerable package outside the body. Depending on your beliefs, you can see it as a design flaw or as unfinished evolution.

Internal or External

It’s not common in nature for testicles to be in a pouch outside the body. There are mammals with testicles in an internal scrotum, nice and safe. Other mammals where the testicles remain inside the body don’t have a scrotum at all. Some assume that human ancestors also had an internal pouch. The question is why this evolved into a vulnerable external scrotum in humans, among others.

Cold Balls

The most accepted theory for this is that the testicles function better at this lower temperature. That the lower temperature is conducive to the quantity and quality of sperm has been demonstrated. To function properly, the testicles need a lower temperature than the rest of the body [1]. The ‘housing’ is designed to regulate this temperature [2,3]. On average and depending on various factors, this is 2 to 4 degrees lower than the 37 degrees in the rest of the body [5]. Special connective tissue and muscles in the lower abdomen can increase and decrease the distance between the testicles and the body. Closer to the body raises the temperature, greater distance provides cooling [5]. It’s like stepping out of an ice bath versus a warm bath. Overweight has been associated with a higher temperature in the scrotum and the associated lower quality of sperm [6]. Recent research has shown that wearing airy boxers contributes to better fertility in men than tight briefs [7]. Actually, that was the whole reason for this article, but I found the “why?” much more interesting. This need for a lower temperature could also be an evolutionary consequence rather than a cause. For example, why don’t humans (anymore?) have the enzymes that allow the testicles to function at higher temperatures, like ancestors with internal testes? And why does it work fine in current mammals with internal testes?

Big Balls for the Alpha

For some reason, I feel super manly when I’m dipping with 80 kilos between my legs. Even if I’m just standing in the dip rack and haven’t done anything yet. Big balls are just a symbol of strength, courage, masculinity, RTL7, and Durex condoms “for men who give orgasms”. Another possible explanation for the fact that the balls moved outside during evolution lies in the ‘social signal’ hypothesis, assuming that the package hangs outside to compete with other males and attract females. Such a function is demonstrated in mammals where the scrotum is brightly colored. However, it does not explain why it’s inconspicuous in many mammals and hidden under fur.

Doggy Style vs. Missionary

An explanation for the name ‘missionary position’ can be found in colonial history. Missionaries were upset about the open display of sex in some cultures and the way it happened. In puritan Christian thought, sex was for reproduction only, and pleasure was sinful. But evolution has made sex pleasurable to promote reproduction. According to some, this not only applies to the choice of the act but also to the result. Most mammals with external testes do it doggy style. Perhaps that’s why the church didn’t like it. Animalistic is instinctive, not civilized. In doggy style, the clitoris can be stimulated by the testicles, which a devout churchgoer shouldn’t have. However, the female orgasm can promote the journey of sperm and thus the chance of fertilization [1]. Clitoral stimulation naturally increases the chance of an orgasm and can therefore indirectly contribute to reproduction. The church hadn’t understood that part of the commandment ‘Go forth and multiply’ yet. Is this the reason for our external testicles? Many mammals that don’t have sex ‘from behind’ (like whales) don’t have external testes, making this hypothesis plausible.

Hanging Balls a Matter of Time?

Are hanging balls a matter of time? And no, I don’t mean that everything sags as you get older. Quite the opposite, as the human race ages. The aforementioned whales now have internal testes, but they show signs of external testes in an evolutionary past. The same goes for turtles [1]. Some consider it possible that the enzymes that enable healthy sperm production at higher temperatures only arose after humans already had external testes. They turn the story around and wonder why some mammals evolved from ‘external’ to ‘internal’ carriers. That seems like a more logical development, evolutionarily speaking. Maybe as humans, we’re just not there yet. Maybe we’ll never get there since we’ve become pretty good at protecting our package.

Warm Balls and Testosterone

Many people won’t be interested in their (current) quality of sperm at all. Not everyone has a baby wish. But what about testosterone? That other important product your testicles provide. That’s hard to say. You would think that warm(er) balls are equally detrimental to your testosterone production as your sperm production and its quality. Some studies support that idea. However, other research seems less convincing. In a 1988 study, the testicles of rats were heated to 41 degrees for half an hour [8]. This had little effect on testosterone production 21 days later. However, it significantly decreased when the temperature was raised between 41.5 and 43 degrees. Similar effects were seen 11 years later. It was easier to find rats than humans who heated their testicles to 43 degrees for 15 minutes [9]. Testosterone nearly halved, and the testes became 65% lighter. A decrease in testosterone was also seen in boars when heated above 38% [10].

‘Sedentary Work and Warm Balls No Effect on Testosterone’

In a 2002 study, men with sedentary jobs were examined [11]. So we’ve now mentioned two adverse effects of sitting in one day that you might not have been aware of yet. This morning it was about the health of your brain, now it’s about the health of your sperm and testosterone. Prolonged sitting can also increase the temperature of the testicles. The 2002 study showed that for every increase of 1 degree Celsius, the sperm concentration of the men decreased by 40%. Testosterone production, however, was not affected. This also applied to the quality of the sperm. However, a year later in 2003, another study followed, this time from Norway. In that study, it was found that the total amount of testosterone in men was highest in the coldest months and lowest in summer. I really don’t know what the implications of such studies could be for men’s fitness fashion. A ventilated flap at the front? A mini air conditioner in your boxers, connected via USB to your phone? Or will we soon be able to buy ice penis sheaths as a testosterone booster?

References

1. Jones, Richard (2013). Human Reproductive Biology. Academic Press.
2. Ivell R. Lifestyle impact and the biology of the human scrotum. Reprod Biol Endocrinol 2007;20:5–15.
3. Skandhan KP Valsa J Melta R. Testicular perfusion apparatus. Urologia 2014;15:0.
4. Song GS Seo JT. Relationship between ambient temperature and heat flux in the scrotal skin. Int J Androl 2009;32:288–294.
5. Kleisner K Ivell R Flegr J. The evolutionary history of testicular externalization and the origin of the scrotum. J Biosci 2010;35:27–37.
6. Andrea Garolla, Mario Torino, Paride Miola, Nicola Caretta, Damiano Pizzol, Massimo Menegazzo, Alessandro Bertoldo, Carlo Foresta;Twenty-four-hour monitoring of scrotal temperature in obese men and men with a varicocele as a mirror of spermatogenic function, Human Reproduction, Volume 30, Issue 5, 1 May 2015, Pages 1006–1013
7. Lidia Mínguez-Alarcón, Audrey J Gaskins, Yu-Han Chiu, Carmen Messerlian, Paige L Williams, Jennifer B Ford, Irene Souter, Russ Hauser, Jorge E Chavarro; Type of underwear worn and markers of testicular function among men attending a fertility center, Human Reproduction, , dey259,
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9. Lue, Y et al. Testicular Heat Exposure Enhances the Suppression of Spermatogenesis by Testosterone in Rats: The “Two-Hit” Approach to Male Contraceptive Development. Endoc. 1999; 141(4)
10. Stone, BA et al. Effects of acute and chronic testicular hyperthermia on levels of testosterone and corticosteroids in plasma of boars. Animal Reproduction Science. 1984; 7(5): 391-403
11. Hjollund, NH et al. Impact of diurnal scrotal temperature on semen quality. Reprod Toxicol. 2002;  16(3): 215-21.
12. Svartberg J et al. Seasonal variation of testosterone and waist to hip ratio in men: the Tromsø study. J Clin Endocrinol Metab. 2003; 88(7): 3099-104.