Men who smoke cannabis have higher sperm counts, scientists puzzled

Leslie Hanson
February 7, 2019

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.

The results were surprising - and show how much more there is to learn about the link between marijuana use and fertility, the scientists said.

The Harvard researchers collected 1,143 health surveys and semen samples from more than 650 men between the years of 2000 and 2017.

A new study from Harvard University researchers found men who smoke marijuana have significantly higher sperm counts than non-tokers.

Just over 50 per cent of the men reported using cannabis; half of these men reported using it in the past, while 11 per cent said they were current users.

Analysis of the semen samples showed that men who had smoked marijuana had average sperm concentrations of 62.7 million sperm per milliliter (million/mL).

There were no significant differences in sperm counts between current and former marijuana smokers. However, Chavarro said his team's paper "does not mean that using more marijuana is going to increase sperm counts, or testosterone or your masculinity".

"These unexpected findings highlight how little we know about the reproductive health effects of marijuana, and in fact of the health effects of marijuana in general", study author Jorge Chavarro, an associate professor of nutrition and epidemiology at Harvard, said in a statement.

However, Chavarro noted that some of those past studies surveyed men who use multiple drugs at once, making it hard to pinpoint the effects of marijuana alone.

Instead, those participants who admitted ever taking the drug turned out to have higher sperm counts than non-users.

On average, the men were 36 years old, mostly white and college educated.

Dr Chavarro said: "It is well-documented that within normal ranges, high testosterone levels are associated with greater engagement in risk-seeking behaviors, including drug use".

Scientists analysed the sperm quality of regular cannabis smokers as well as non-smokers, with some unexpected results.

Past studies have claimed that using the drug could lower a man's sperm count. Participants were asked to fill in questionnaires detailing their history of cannabis use.

On the other hand the association could have nothing to do with the effects of cannabis.

Dr Feiby's point of view was seconded by leading British expert, Allan Pacey who said that the high testosterone in men's bodies could the reason why these men smoke weed. The men in that study who used marijuana at least once per week, in addition to other recreational drugs, had even lower sperm counts, the researchers found.

"An equally plausible interpretation is that our findings could reflect the fact that men with higher testosterone levels are more likely to engage in risk-seeking behaviours, including smoking marijuana". "In my opinion, this should be avoided at all costs in any couples trying to start a family".

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