One widely circulated 2014 study involving almost 2,000 British men - the world's largest study to explore how common lifestyle factors influence sperm morphology (the size and shape of sperm) - found that males under 30 with less than four-per-cent normal sperm were almost twice as likely to have used cannabis in the previous three months.
Additionally, researchers of the current study said the doses of marijuana used by participants may have varied from the doses of participants in past studies, therefore skewing the results. They also found that the sperm counts did not differ very much when comparing current and former cannabis smokers.
Animal studies have shown that cannabinoid receptors play a part in the male reproductive system, Chavarro said.
In addition, among marijuana smokers, greater use was associated with higher serum testosterone levels.
According to the study, men who smoked marijuana had average sperm concentrations of 62.7 million sperm per milliliter of ejaculate while men who had never smoked marijuana had average concentrations of 45.4 million sperm per milliliter of ejaculate.
The latest study's senior author, Dr. Jorge Chavarro, said the unexpected findings "highlight that we know too little about the reproductive health effects of cannabis and, in fact, of the health effects in general, to make strong statements about the impact of cannabis on health, with the possible exception of mental health. Secondly, the study is a great opportunity to spark interest on investigating the health effects of marijuana particularly with the backdrop of increasing legalization of recreational use in the USA coupled with a greater perception that marijuana poses no health risks".
"There could be a non-causal explanation, such as the effect of the male hormone testosterone on both sperm count and risk-taking behaviour such as smoking cannabis", said U.S. lead researcher Dr Jorge Chavarro, from the Harvard TH Chan School of Public Health in Boston. Meanwhile, 12 percent of non-cannabis consumers tested below that threshold for a normal sperm count.
But the authors also say there are a few legitimate reasons why marijuana use really might be tied to higher sperm quality.
Is Marijuana Good For The Reproductive Health?
It is estimated that 16.5% of adults in the USA use marijuana, and support for legal recreational use of marijuana has increased dramatically in recent years.
However, the new experiment, published Feb.6 in the issue of Journal Human Reproduction, does not urge men to start smoking the plant to up their sperm count. It may be that low or moderate levels of marijuana use have a beneficial effect on sperm production, but heavier use reverses this effect.
However the authors wrote that their findings may not relate to the general population, and said their study was limited by the fact they relied on the men reporting their use of cannabis accurately.
A Man Smoking Marijuana. She also cautions that the results may not apply to all men, as the study consisted of men who were seeking fertility treatment with their partners at a fertility center.
A new study out of Harvard might complicate the narrative around pot's potential health risks, at least when it comes to men's fertility.
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