Harvard study links marijuana smoking with higher sperm concentrations

Posted at 3:41 PM, Feb 10, 2019
and last updated 2019-02-10 17:41:57-05

BOSTON, MA – A new study out of Harvard has linked marijuana smoking with higher sperm concentrations.

According to the study, men who had smoked marijuana at some point in their life had significantly higher concentrations of sperm when compared with men who had never smoked marijuana.

The study, which was led by Harvard T.H. Chan School of Public Health, also found that there was no significant difference in sperm concentrations between current and former marijuana smokers.

“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,” said Jorge Chavarro, associate professor of nutrition and epidemiology at Harvard Chan School. “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”

Prior to beginning the study, which was published on Feb. 5, 2019, researchers hypothesized that marijuana smoking would be associated with worse semen quality. Previous studies had suggested that marijuana use was associated with negative effects on male reproductive health, but most of those studies were focused on animal models or on men with histories of drug abuse, according to Harvard.

According to the school, researchers collected 1,143 semen samples from 662 men between 2000 and 2017. On average, the men were 36-years-old, mostly white, and college educated. Researchers used a self-reported questionnaire that asked men about their marijuana usage.

The study said 55 percent of participants reported having smoked marijuana at some point in their lives. 44 percent reported past use of marijuana, and 11 percent said they were current smokers.

Analysis of the semen samples showed men who had smoked marijuana had average sperm concentrations of 62.7 million sperm per milliliter, while men who had never smoked had average concentrations of 45.4 million sperm per milliliter. Harvard said the study also showed only 5 percent of smokers had sperm concentrations below 15 million per milliliter, which is the World Health Organization’s threshold for “normal” levels. This is compared to 12 percent of men who had never smoked marijuana.

The school also reported that the study found that among marijuana smokers, greater use was associated with higher serum testosterone levels.

Harvard reported that researchers cautioned that there were several potential limitations to the findings, including that participants may have underreported marijuana use due to its status as an illegal drug for most of the study period. They also stated that there are few similar studies to compare their results against.

“Our findings were contrary to what we initially hypothesized. However, they are consistent with two different interpretations, the first being that low levels of marijuana use could benefit sperm production because of its effect on the endocannabinoid system, which is known to play a role in fertility, but those benefits are lost with higher levels of marijuana consumption,” said Feiby Nassan, lead author of the study and a postdoctoral research fellow at Harvard Chan School. “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 behaviors, including smoking marijuana.”