Pacey and his team went to 14 fertility clinics in the UK and samples of 2,249 men at least 18 years of age were collected. 1,970 of these samples had reliable results sperm morphology. A man must have at least 40 million sperm in each 2 ml of ejaculate, and if at least 4% of them are the right size and shape, sperm morphology is normal. The researchers found that 318 men in the study were below normal. The remaining 1,652 men with normal morphology were considered the control group.
Participants in the study were asked to self-report certain lifestyle factors such as smoking cigarettes, drinking alcohol, and recreational drug use. The researchers also noted the season samples were donated, as the heat can affect sperm morphology (hence the testicles outside the body).
Men under 30 years whose normal sperm morphology was less than 4% were more likely to have smoked marijuana during the three months before giving the sample and the control group. The age of 30 is somewhat arbitrary; while research has shown sperm quality actually decreases with age, there is no definitive threshold for reduced fertility as there are women. These men were also more likely to have taken the sample during the summer, which may have affected the morphology as well. 72 days are needed for sperm to mature, so any exposure to heat or drugs during this time may well affect sperm quality. Further study will be completed, controlling for factors such as heat and trauma, to verify or exonerate marijuana as a causative agent.
“Our understanding of the factors that influence the size and shape of sperm is very limited, but faced with a diagnosis of poor sperm morphology, many men are concerned to try to identify the factors of their lifestyle could be causing this, “Pacey said in a press release. “It is therefore reassuring to find that there are very few identifiable risks, although our data suggest that cannabis could be advised to stop using the medicine if you are planning to try to raise a family.”
The researchers found no link with other factors like smoking cigarettes or drinking, but those planning to have a baby, you should probably cut back on those as well.
This study is based off of previous research Pacey co-author in 2012 when the team explored the lifestyle factors that influenced the motility of sperm. That study also found some things that men can change in order to increase their motility. However, the study only looked at factors like smoking or drinking habits, and never analyzed the quality of DNA carried by the sperm, which may have yielded different results.
Cannabis is not the only factor found to influence the morphology of sperm. In a paper published in the Journal of Occupational and Environmental Medicine describes men who work with chemicals such as paint removers or lead would also be more likely to have a lower percentage of normal sperm. Previously, it was shown that men usually had exposure to organic solvents were more likely to have slower swimming sperm.