Study: Men who want to have children may want to dial back their marijuana habit

"A large percentage of miscarriages are unexplained."


Scientists know that smoking marijuana affects the genetic profile of sperm and that the male body is hardwired to respond to cannabinoid chemicals. What this exactly means for men’s reproductive health is less understood: Some studies show smoking leads to higher sperm counts, while others show cannabis use leads to a lower sperm count.

Now, new research indicates that regardless of sperm count, marijuana use could affect reproductive health in a very challenging way. On Monday, a team of Boston University researchers announced at the American Society for Reproductive Medicine Congress & Expo an association between paternal marijuana use and the likelihood of miscarriage.

Ultimately, they discovered that men who smoked marijuana once a week or more, had partners that were twice as likely to experience a miscarriage. While this study cannot prove a direct cause-and-effect link, lead researcher Alyssa Harlow says this does put forth the possibility that marijuana causes sperm DNA damage.

"It’s important we understand whether male factors may contribute to the risk of miscarriage

“A large percentage of miscarriages are unexplained, and it’s important we understand whether male factors may contribute to the risk of miscarriage,” Harlow tells Inverse. “There have been some studies to show that marijuana use may impact sperm quality and result in DNA damage which might contribute to miscarriages.”

Harlow and her team evaluated the data of 1,413 couples enrolled in the the Pregnancy Study Online (PRESTO), a web-based research study that examines how lifestyle factors may, or may not, have an impact on fertility and pregnancy. Couples completed surveys on lifestyle factors, like smoking status and alcohol intake, were asked to complete follow-up questionnaires at about 12 weeks gestation and at about 32 weeks gestation.

THC affects the genetic profile of sperm.

Sarah Calvert / University of Sheffield

After the team controlled for all other factors except for male marijuana-smoking, certain patterns emerged. They found that eight percent of men said they used marijuana at least once a week over the past few months. Meanwhile, 18.8 percent of the couples overall experienced a miscarriage.

In turn, the data shows that couples with male partners who use marijuana at least once per week during preconception had a “greater risk of spontaneous abortion compared with no male marijuana use.” The Adjusted Hazard Ratios for male marijuana use were 1.07 for men who consumed marijuana less than once a week and 2.04 for those who did so more than once a week.

“We were a little surprised by how strong the association was,” explains Harlow, “And that the results really persisted after controlling for a number of lifestyle and behavioral factors, including female marijuana use.”

John Mitchell, Ph.D., is an assistant professor at Duke University Medical Center whose previously examined how smoking marijuana affects the genetic profile of sperm cells. He was not a part of this new study, but views it as an intriguing next step in a field where more research is needed.

“Our study demonstrated that DNA methylation differed between cannabis users and non-users, indicating that cannabis use may increase pre-conception paternal reproductive risks,” Mitchell explains.

“Studies like this new one on paternal cannabis use and miscarriage are needed as a next step — there’s a gap in knowledge in terms of what we know about paternal reproductive risk and cannabis use, including impact [if any] on offspring and the quality of a pregnancy.”

Adjusted Hazard Ratios were 2.04 for men who consumed marijuana more than once a week. 

Dank Depot/Flickr Creative Commons

For now, Harlow notes that more studies are needed to confirm her team’s findings before conclusions are made — especially those that incorporate a more detailed look at “marijuana use measurement,” including dosages.

But this study does shine a light on a subject not as frequently discussed when it comes to fertility: The role of men.

“I think that’s part of the reason why this study is getting so much attention, because we’re used to putting all the focus, all the blame, all the stress on the women and the world of male fertility is really exploding,” Jennifer Ashton, M.D., commented on “Good Morning America.”

“Forty percent of couples’ infertility is due to male factors so it bears repeating we need to focus on the men just as much as the women.”

Objective: Frequent marijuana use has been associated with poor semen quality. Though evidence is mixed, most studies show deleterious effects. There are no studies of male marijuana use and adverse pregnancy outcomes. We evaluated the association between male marijuana use and spontaneous abortion (SAB).
Design: Prospective cohort study.
Materials and methods: This analysis uses data from 1,413 couples enrolled in Pregnancy Study Online (PRESTO), a North American preconception cohort study of pregnancy planners. At baseline (preconception), men and women separately reported demographics, medical history, and lifestyle/behavioral factors, including marijuana use frequency. Women completed bimonthly follow-up surveys for up to 12-months or until conception. Data on SAB were ascertained from follow-up questionnaires completed in early pregnancy (<12 weeks gestation) and late pregnancy (~32 weeks gestation). Additional data were reported on the first positive pregnancy test date, due date, and gestational weeks at loss. Frequency of male marijuana use in the previous 2 months was ascertained at baseline and categorized as follows: no use, <1 time/week, or ≥1 time/week. Cox proportional hazards regression models were used to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association between male baseline marijuana use frequency and SAB. The timescale was gestational weeks from date of first pregnancy detection. We controlled for age at baseline (male and female), household income, education, race/ethnicity, smoking status, environmental tobacco exposure, alcohol intake, caffeine intake, sugar-sweetened beverage intake, body mass index, exercise, multivitamin use, sleep duration, hours of work per week, history of sexually transmitted infections, depression/anxiety, and frequency of female baseline marijuana use. Additional models controlled for reproductive history, including having impregnated a partner previously, parity (female), history of pregnancy loss (female), and family history of SAB (female).
Results: Among the 1,413 couples followed, 1,164 (82.4%) men reported no marijuana use, 132 (9.3%) reported using marijuana <1 time/week, and 117 (8.3%) reported using marijuana ≥1 time/week in the 2 months before baseline. During follow-up, 266 (18.8%) SABs were reported. Compared with no male marijuana use, adjusted HRs for male marijuana use <1 time/week and ≥1 time/week were 1.07 (95% CI: 0.65-1.77) and 2.04 (95% CI: 1.28-3.24), respectively. The association (≥1 time/week vs. none) persisted after adjusting for reproductive history (HR=2.05, 95% CI: 1.29-3.26), and was slightly stronger after restricting to couples where the female partner did not use marijuana (HR=2.19, 95% CI: 1.26-3.80).
Conclusions: Couples with male partners who used marijuana ≥1 time per week during preconception had a greater risk of SAB compared with no male marijuana use. Little association was found for men who used marijuana <1 time per week. Possible mechanisms include an adverse effect of frequent marijuana use on sperm quality.
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