Men who smoke marijuana may have a higher sperm count than those who have never used the drug, according to a surprising new study.
The results are "not consistent" with previous research, which suggests that marijuana has a detrimental effect on male testicular function, the researchers said.
However, the study, published in the February 6 issue of the journal Human Reproduction, does not mean that men should start smoking marijuana to increase their sperm count.
The findings are far from conclusive, and further research is needed to understand whether smoking marijuana could indeed, at certain levels, have a positive effect on sperm production.
But the study highlights how researchers know little about the effects of marijuana on reproductive health, studies senior author Dr. Jorge Chavarro, an associate professor of nutrition and epidemiology at Harvard T.H. Chan School of Public Health in Boston said in a statement. "We know much less than we think we know." [25 Odd Facts About Marijuana]
Marijuana and sperm
Previous studies have suggested that smoking marijuana can reduce a man's sperm count, especially among heavy users. For example, in 2015, researchers in Denmark found that men who smoked marijuana more than once a week had sperm counts that were nearly 30% lower than those who did not smoke marijuana, or those who used the drug less often.
However, the effects of more moderate marijuana use on sperm counts among men are less clear.
In the new study, the researchers analyzed information from 662 men who, along with their partners, were evaluated for infertility from 2000 to 2017 at the Massachusetts General Hospital's Fertility Center. The men answered questions about how many times they smoked marijuana or used other drugs, and also provided sperm and blood samples.
Overall, just over half of men (55 percent) reported smoking marijuana during their lives, and 11 percent said they smoked marijuana at the time.
The researchers found that men who reported having smoked marijuana had an average sperm concentration of 63 million sperm per milliliter of semen compared to 45 million sperm per milliliter of semen among those who never used marijuana. The findings were retained even after researchers took into account factors that could affect sperm concentration, such as age, smoking, and alcohol use.
In addition, only 5% of marijuana smokers had below-normal sperm concentrations – that is, less than 15 million sperm per milliliter of semen. Among men who never smoked marijuana, 12% had below-normal sperm concentrations.
Among men who smoked marijuana, those who used it most often had higher testosterone levels than those who used it less often.
Interestingly, every year that has passed since a man used marijuana for the last time was associated with a slight increase in sperm count.
"Our findings were contrary to what we assumed at the beginning of the study," said lead author of the study, Feiby Nassan, a postdoctoral fellow at Harvard T.H. Chan School of Public Health said in a statement.
But the study can be interpreted in several ways. It may be that low or moderate levels of marijuana use have a beneficial effect on sperm production, but heavier use reverses this effect. Or, it may also be that men with higher levels of testosterone are more likely to engage in "risky" behaviors, such as drug use; and researchers have found the link between marijuana and sperm count "because men with higher testosterone, within normal levels, have a higher sperm count and are more likely to smoke marijuana," Nassan said.
Jury still out
It is known that moderate to heavy use of tobacco or alcohol is linked to lower sperm count but if marijuana has the same effect it is under debate, said Dr. Sarah Vij, a urologist at the Cleveland Clinic who was not involved with the drug. study.
Vij said he applauded the study's authors for looking at this issue, as it is a topic that needs further research.
But the new study does not provide a conclusive answer. "Overall, the jury is still out on how marijuana affects a man's fertility potential," Vij told Live Science.
Vij noted that both marijuana users and non-users of the study had, on average, normal sperm counts. Therefore, the study can not draw conclusions about whether marijuana use is linked to improved fertility.
In addition, it takes about three months for men to undergo a full cycle of sperm production to produce mature sperm. That means that using marijuana years ago "really should not have any impact on [a man’s] state of fertility, "Vij said.
And yet the study also found that men who said they had used marijuana for at least a year had higher sperm counts than men who used it more recently. Vij said he wondered if "there is something going along with the use of marijuana" that is linked to better production of sperm.
The researchers also noted that the study was conducted among men who visited a fertility clinic and therefore the results may not necessarily apply to the general population. In addition, the men in the study self-reported their use of marijuana, and it is possible that some participants were not true about their use of marijuana due to the social stigma or illegal status of the drug in Massachusetts at the time the data were collected.
Originally published in Living Science.