In a surprising report published in the journal Human Reproduction scientists from Harvard revealed their results of smoking marijuana on sperm health. Apparently, it may be good for it! The authors, led by Dr. Feiby L Nassan, cautioned that this result is surprising because they are "not consistent with a deleterious effect of marijuana on testicular function". They also caution that men should not go running to their nearest dispensary based on their study. However, the study does highlight the lack of quality research out there on how marijuana affects the body.
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The researchers used samples from a population of men at a local fertility clinic to study the association between self-reported marijuana smoking and markers of testicular function. Markers for semen quality used in this study included sperm concentration, sperm DNA fragmentation, and serum reproductive hormones. In line with the previous literature on the subject, the authors themselves predicted a negative effect of marijuana smoking on testicular hormones. Boy were they surprised.
Their results showed a significantly higher sperm concentration in men with a prior history of smoking marijuana than those who did not (average sperm concentration of 63 million sperm per milliliter of semen, compared with 45 million sperm per milliliter of semen among those who had never used marijuana). Nevertheless, there were no associations of a history of marijuana with other measures, such as markers of sperm DNA integrity or other reproductive hormone concentrations.
Because these results were unexpected, the researchers re-categorizing marijuana smoking based on the last time of reported use and after restricting analyses to men without a diagnosis of male factor infertility. Further analyses looked only at the first semen sample per man and further adjusted for stress levels or history of STDs. Finally, the researchers adjusted for time of sample collection to testosterone analysis. Despite this deep analysis, the main findings remained the same.
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The authors pointed out the various flaws in previous studies, some of which are over 30 years old. These studies used men with a much wider history of multi-drug abuse, which may have confounded their results. The most recent comparative study, performed in 2015 in a population of Danish men, found that marijuana decreased sperm concentration. Yet, the authors of the present study raised the possibility that the amount of marijuana smoked could be a factor in determining the effects of marijuana. Thus, they proposed that marijuana could increase concentration in moderate users, but greater use could lead to low concentrations. This is a common pharmacological process known as the "inverted U-shaped curve" and is present in many physiological functions, such as stress.
One final interesting piece in this puzzle is the data from animal studies which show a role for the endocannabinoid system in spermiogenesis. Apparently, genetic inactivation of the endocannabinoid receptor CB1 in mice causes DNA damage in sperm. Also, in genetic CB1 knock-out mice sperm lose the ability to function normally. The results of the current study are surprising compared to the human but not the animal literature. This means that their results should be interpreted very carefully. Ultimately, more experimental studies on animals and humans are needed to determine what to do with the results.
See the video below detailing the complex results of studies on smoking and overall sperm health.
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Source: Human Reproduction, Fertility and Sterility, www.livescience.com, Advances in the Biosciences, American Journal of Epidemiology, www.mindtools.com, Proceedings of the National Academy of Science of the United States of America, Frontiers in Endocrinology, Endocrinology, General and Comparative Endocrinology