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Marijuana smoking impairs sperm quality, fertility

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A new study evaluated the impact on sperm quality by lifestyle choices including self-reported exposures to alcohol, tobacco, recreational drugs, as well as occupational and other factors. They found a significant association between poor sperm quality and marijuana use. The findings were published online on June 4 in the journal Human Reproduction by researchers in the United Kingdom and Canada.

The study authors note that a number of studies have reported that that men's lifestyle choices can affect sperm morphology (sperm size and shape); however, the evidence is weak because the studies often were underpowered and poorly controlled. Therefore, they conducted a large study to evaluate the effect of lifestyle choices on sperm morphology. They compared lifestyle choices between 318 men with poor sperm morphology and 1,652 men with normal sperm morphology. Poor sperm morphology was based on a semen analysis that found less than 4% normal forms among 200 sperm assessed). Exposures included self-reported exposures to alcohol, tobacco, recreational drugs, as well as occupational and other factors.

The men eligible for the study were aged 18 years or older who were recruited from 14 fertility clinics across the United Kingdom during a 37-month period beginning on January 1, 1999. They were part of a couple who had been attempting conception without success following at least 12 months of unprotected intercourse; they also had no knowledge of any semen analysis before being enrolled in the study.

The investigators found that risk factors for poor sperm morphology included: (1) sample production in summer (1.99-fold increased risk); and (2) use of cannabis in the three months prior to sample collection in men aged 30 years or younger (1.94-fold increased risk). Men who produced a sample after six days abstinence were less likely to be found to have poor sperm morphology (0.64-fold decreased risk). No significant relationship was found with body mass index (BMI), type of underwear, smoking tobacco, alcohol consumption, or having a history of mumps.

The authors concluded that marijuana use was the only habit they studied to be strongly associated with abnormal sperm morphology. They noted that their study suggested, that aside from cannabis use, an individual's lifestyle has very little impact on sperm morphology and that delaying assisted conception to make changes to lifestyle is unlikely to increase the likelihood of conception.

The authors noted some limitations of the study. The data were collected blind to outcome; therefore, exposure information should not have been subject to reporting bias. Less than half the men attending the various infertility clinics met the study eligibility criteria; among those who did, two out of five did not participate. The authors noted that it is not known whether any of those who refused to take part did so because they had a lifestyle which they did not want subjected to investigation. They explained that the power of the study was adequate to draw conclusions regarding common lifestyle choices; however, this is not the case for exposures that were rare or poorly reported.

The authors are affiliated with the University of Sheffield (Sheffield, UK), University of Manchester (Manchester, UK), and University of Alberta (Edmonton, Canada).