Occasional cannabis may boost men's fertility, new study suggests

SHOCK The scientists found the study went against their hypothesis

The volunteers were asked whether they had ever smoked more than two joints or the equivalent amount of marijuana in their lives and if they were current smokers.

The result came as a big surprise to scientists measuring the sperm counts of more than 600 men from couples attending a fertility clinic.

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". Cocaine use was associated with a higher estimated proportion of men (12 %) having sperm concentration below World Health Organization reference values.

In total, 55 percent of the men admitted to trying cannabis at some point in their lives, while 44 percent said they were regular users in the past.

"We spent a good two months redoing everything, making sure that there wasn't any error in the data", Cahvarro was quoted by Bloomberg.

"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", says Feiby Nassan, a researcher in environmental health and nutrition at Harvard.

More than one study (including one last December) has suggested that cannabis could lower men's sperm counts or otherwise negatively affect their reproductive health. However, Chavarro's study found that only five percent of marijuana consumers had less than 15 million sperm per milliliter of ejaculate, which would put them under normal semen levels. Although the study of moderate marijuana use on sperm count among men is still unclear or "less clear". 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".

In addition, among marijuana smokers, greater use was associated with higher serum testosterone levels. By comparison, 12 percent of men who never tried marijuana had below-normal sperm levels, the findings showed.

Nassan also said that the results may have been skewed by cannabis prohibition. "For example, the observation that men in this study who had ever (but not currently) smoked marijuana had a higher sperm concentration compared to those who had never done so is intriguing".

The Harvard researchers collected 1,143 health surveys and semen samples from more than 650 men between the years of 2000 and 2017. Additionally, 317 of the participants provided blood samples that were analyzed for reproductive hormones. There were no statistically significant differences in sperm concentration between current and past cannabis smokers. Other research revealed marijuana use reduced sperm motility and ejaculate volume.

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. First, these findings are consistent with a U-shaped relation whereby low levels of cannabis use could benefit sperm production due to the well-known role played by the endocannabinoid system, but potential beneficial effects reverse at higher levels of use.

None of these limitations or considerations invalidate study's findings, it's just a sign, as Chavarro said, that we need to study cannabis more (the fact that cannabis is still considered more risky than opioids by the USA government remains a roadblock to that research, incidentally).

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