Men who have smoked marijuana at some point in their life had significantly higher concentrations of sperm when compared with men who have never smoked marijuana, according to new research led by Harvard TH Chan School of Public Health. The study, conducted in the Fertility Clinic at Massachusetts General Hospital, 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 TH Chan School of Public Health. “Our results need to be interpreted with caution and they highlight the need to further study the health effects of marijuana use.”
It is estimated that 16.5% of adults in the US use marijuana, and support for legal recreational use of marijuana has increased dramatically in recent years. Understanding the health effects associated with marijuana use is important given the growing perception that it poses few health hazards.
The researchers hypothesised that marijuana smoking would be associated with worse semen quality. Previous studies on marijuana have suggested that it is associated with negative effects on male reproductive health, but most of those studies had focused on animal models or on men with histories of drug abuse.
For this study, researchers collected 1,143 semen samples from 662 men between 2000 and 2017. On average, the men were 36 years old, and most were white and college educated. Additionally, 317 of the participants provided blood samples that were analysed for reproductive hormones. To gather information on marijuana use among study participants, researchers used a self-reported questionnaire that asked the men a number of questions about their usage, including if they had ever smoked more than two joints or the equivalent amount of marijuana in their life and if they were current marijuana smokers.
Among the participants, 365, or 55%, reported having smoked marijuana at some point. Of those, 44% said they were past marijuana smokers and 11% classified themselves as current smokers. Analysis of the semen samples showed that men who had smoked marijuana had average sperm concentrations of 62.7m sperm per ml of ejaculate while men who had never smoked marijuana had average concentrations of 45.4m sperm per ml of ejaculate. Only 5% of marijuana smokers had sperm concentrations below 15m/ml (the World Health Organisation threshold for “normal” levels) compared with 12% of men who had never smoked marijuana.
The study also found that among marijuana smokers, greater use was associated with higher serum testosterone levels.
The researchers cautioned that there are several potential limitations to the findings, including that participants may have underreported marijuana use given its status as an illegal drug for most of the study period.
The researchers emphasised that they do not know to what extent these findings may apply to men in the general population as the study population consisted of sub-fertile men in couples seeking treatment at a fertility centre. Additionally, they noted 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 behaviours, including smoking marijuana.”
Study Question: Is marijuana smoking associated with semen quality, sperm DNA integrity or serum concentrations of reproductive hormones among subfertile men?
Summary Answer: Men who had ever smoked marijuana had higher sperm concentration and count and lower serum FSH concentrations than men who had never smoked marijuana; no differences were observed between current and past marijuana smokers.
What Is Known Already: Studies of marijuana abuse in humans and animal models of exposure to marijuana suggest that marijuana smoking adversely impacts spermatogenesis. Data is less clear for moderate consumption levels and multiple studies have found higher serum testosterone concentrations among marijuana consumers.
Study Design, Size, Duration: This longitudinal study included 662 subfertile men enrolled at the Massachusetts General Hospital Fertility Center between 2000 and 2017. The men provided a total of 1143 semen samples; 317 men also provided blood samples in which we measured reproductive hormones.
Participants/Materials/Setting/Methods: Use of marijuana and other drugs was self-reported at baseline. Standard protocols were followed for measuring semen quality, sex hormones and DNA integrity. We used linear mixed effect models with a random intercept to evaluate the associations of self-reported marijuana smoking at enrolment with semen parameters from subsequently collected samples, and linear regression models for sperm DNA integrity and serum reproductive hormones, while adjusting for confounders including smoking and cocaine use.
Main results and the role of chance: Men who had ever smoked marijuana (N = 365) had signiﬁcantly higher sperm concentration (62.7 (95% conﬁdence interval: 56.0, 70.3) million/mL) than men who had never smoked marijuana (N = 297) (45.4 (38.6, 53.3) million/mL) after adjusting for potential confounders (P=0.0003). There were no signiﬁcant differences in sperm concentration between current (N=74) (59.5(47.3,74.8)m/mL) and past marijuana smokers (N=291)(63.5(56.1,72.0)m/mL; P=0.60) A similar pattern was observed for total sperm count. Furthermore, the adjusted prevalence of sperm concentration and total sperm motility below WHO reference values among marijuana smokers was less than half that of never marijuana smokers. Marijuana smokers had signiﬁcantly lower follicle stimulating hormone (FSH) concentrations than never marijuana smokers (−16% (−27%, −4%)) and there were no signiﬁcant differences between current and past marijuana smokers (P = 0.53). Marijuana smoking was not associated with other semen parameters, with markers of sperm DNA integrity or with reproductive hormones other than FSH. Chance ﬁndings cannot be excluded due to the multiple comparisons.
Feiby L Nassan, Mariel Arvizu, Lidia Mínguez-Alarcón, Paige L Williams, Jill Attaman, John Petrozza, Russ Hauser, Jorge Chavarro, Jennifer B Ford, Myra G Keller