Cannabis users may be seeing their fertility go up in smoke, claims a Manchester University study.
The research, completed in conjunction with the University of Sheffield, showed that the drug affected the size and shape of sperm, while booze binges and smoking had little effect.
The world’s largest study also showed that sperm size and shape were worse in the summer – but better for men who refrained from sexual activity (referred to as sperm morphology) for more than six days.
Dr Andrew Povey, from the University of Manchester’s Institute of Population Health, said: “This research builds on our study of two years ago which looked at the risk factors associated with the number of swimming sperm (motile concentration) in men’s ejaculates.
“This previous study also found that there were relatively few risk factors that men could change in order to improve their fertility.
“We, therefore, have to conclude again that there is little evidence that delaying fertility treatment to make adjustments to a man’s lifestyle is unlikely to improve their chances of a conception.”
The study, published in the medical journal Human Reproduction, recruited 2,249 men from 14 fertility clinics around the UK and asked them to fill out detailed questionnaires about their medical history and their lifestyle.
Reliable data about sperm morphology was only available for 1,970 and so the researchers compared the information collected for 318 men who produced sperm with less than four per cent of sperm with correct size and shape.
This was also true of a control group of 1,652 men where this was above four per cent and therefore considered ‘normal’ by current medical definitions.
Men who produced ejaculates with greater than four per cent normal sperm were nearly twice as likely to have produced a sample in the summer months (June to August).
They were also more likely to produce a sample if they were older than 30 and used cannabis in the three-month period prior to ejaculation.
However, other factors can also impact sperm morphology.
Professor Nicola Cherry, originally from The University of Manchester but now at the University of Alberta in Canada, said: “In addition to the cannabis exposure shown in this paper, we also know that men exposed to paint strippers and lead are also at risk of having sperm with poor morphology.”
Previous research has suggested that only sperm with good sperm morphology are able to pass into the woman’s body following sex and make their way to the egg and fertilise it.
Studies in the laboratory also suggest that sperm with poor morphology also swim less well because their abnormal shape makes them less efficient.
Although the study failed to find any association between sperm morphology and other common lifestyle factors, such as cigarette smoking or alcohol consumption, it remains possible that they could correlate with other aspects of sperm.
Factors like the quality of the DNA contained in the sperm head were not measured in the researched.
Lead author Dr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield, said: “Our knowledge of factors that influence sperm size and shape is very limited.
“Yet, faced with a diagnosis of poor sperm morphology many men are concerned to try and identify any factors in their lifestyle that could be causing this.
“It is therefore reassuring to find that there are very few identifiable risks, although our data suggests that cannabis users might be advised to stop using the drug if they are planning to try and start a family.”
The study, funded by the UK Health and Safety Executive, the UK Department of Environment, Transport and the Regions, the UK Department of Health and the European Chemical Industry Council, follows on from the team’s previous research.
Previous studies showed that men who worked with organic solvents, particularly glycol ethers, were more likely to ejaculate lower numbers of swimming sperm.
Image courtesy of Bjorn Hansen with thanks
