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Cannabis Reduces Sperm Quality in Adult Mice And Their Sons, Study Finds

By Alexander Beadle

Published: Dec 08, 2021   
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Regular exposure to cannabis lowers the sperm count and sperm motility of mice, according to a new study from researchers at Washington State University.

Published in the journal Toxicological Sciences, the study found that these metrics were not only reduced in the mice directly exposed to cannabis – but also in the next generation of direct male offspring. With recent estimates indicating that sperm counts in humans have dropped by around 50 to 60 percent in the last few decades, the researchers behind the new mouse study say that their findings should give cannabis consumers some pause.

“This is a warning flag. You may take cannabis for some kind of momentary stress, but it could affect your offspring,” study author Dr Kanako Hayashi, associate professor in the Washington State University School of Molecular Biosciences, commented in a press statement.

Sperm counts and sperm motility decrease with regular cannabis exposure

Unlike human studies on cannabis and reproductive function, which typically rely on self-report surveys, animal studies allow researchers to more precisely control experimental circumstances and variables.

In this study, the researchers exposed 15 adult male mice to vaporized cannabis flower three times a day for ten days. Another 15 adult male mice were left unexposed to act as a control group, and the sperm count and sperm motility (the ability of sperm to swim the right way) were compared between the two groups at the end of the experiment.

This exposure frequency may seem high, but the researchers say it was chosen to try and replicate frequent cannabis use in humans. This was also the first mouse reproductive study to use vaporized whole cannabis – previous animal studies have most commonly used THC injections as an administration method – in order to closer emulate real human drug use.

Immediately after the ten-day cannabis exposure period, the researchers observed that sperm motility had decreased in the mice exposed to cannabis. After one month, the sperm counts were lower than the control group.

There were also signs of disruption to normal germ cell development, with further analyses showing an abnormal distribution of sperm development stages in these mice. Interestingly, there appeared to be no problems with testosterone levels in these mice. However, the researchers did see dysregulation of two enzymes present in the mice’s testis (Cyp11a1 and Cyp19a1) that are known to play a role in sperm production.

Negative effects on reproductive health may extend to the next generation

This group of cannabis-exposed mice were bred with unexposed female mice to produce a new generation of offspring. When the sons of the cannabis-exposed group were examined, it was found that they also had reduced sperm counts and sperm motility. Additionally, the sons also displayed evidence of DNA damage and some disruption of gene expression related to sperm cell development.

“We were not expecting that the sperm would be completely gone or that motility would be completely offset, but the reduction in sperm count and motility of the offspring, the sons, is probably a direct effect of the cannabis exposure to father,” explained Hayashi.

The sons were also bred with female mice to produce a third generation of mice, the grandsons of the original group that were exposed to cannabis. However, the DNA damage and altered gene expression were not seen in this generation. The researchers say this may suggest that cannabis impacted the second-generation of mice at a developmental stage.

Related to this, Hayashi and her colleagues are now investigating whether cannabis exposure to mice in utero might extend these generational effects to further generations.

Cannabis and fertility

Investigating the effects of cannabis on reproductive health is important as existing research indicates that the human body’s internal endocannabinoid system may play a direct role in the development of the testis and maintaining testicular health.

One research study published in Scientific Reports in 2019 found that activation of the endocannabinoid system – by using cannabis, for example – could affect the natural regulation of the testis.

​​“I was surprised to find that endocannabinoids were so widely expressed in all cell types in the testis, both in the germ cells and the hormone-producing cells,” lead study author Professor Niels E. Skakkebaek, told Technology Networks shortly after the publication of the study.

For this study, the researchers looked at testis tissue taken from 15 patients with testicular germ cell cancer. After detecting one of the major endocannabinoids in the tissue, the research term found a distinct pattern of endocannabinoid system components that were present across different stages of testis development.

“Andrologists like me have for generations been focusing on other hormone aspects, but overlooked the possibility that endocannabinoids may participate in the normal sperm and hormone production,” Skakkebaek explained.

“We did see a hint a couple of years ago, when we found that young Danish men who had used marijuana had significantly poorer sperm counts than their peers.”

Interestingly, another human study of cannabis use and male fertility found that men who reported smoking cannabis at some point in their life had higher sperm concentrations than those who had never used cannabis.

The men who reported heavier cannabis use in this study also tended to have higher testosterone levels, possibly due to the fact that men with higher testosterone levels are more likely to demonstrate risk-seeking behaviors such as cannabis use. As testosterone is normally positively related to sperm count, the researchers suggest that this could explain this observation. However, more research is still needed to fully characterize the relationship between cannabis use and healthy reproductive function in males.


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