Young men who use cannabis may be putting their fertility at risk by inadvertently affecting the size and shape of their sperm according to research published today.
In the world’s largest study to investigate how common lifestyle factors influence the size and shape of sperm (referred to as sperm morphology), a research team from the Universities of Sheffield and Manchester also found that sperm size and shape was worse in samples ejaculated in the summer months but was better in men who had abstained from sexual activity for more than six days.
However, other common lifestyle factors reported by men, including smoking cigarettes or drinking alcohol, appeared to have little effect.
The study, published in the medical journal Human Reproduction, recruited 2,249 men from 14 fertility clinics around the UK1 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 and 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 percent normal sperm were nearly twice as likely to have produced a sample in the summer months (June to August) or if they were older than 30 years old to have used cannabis in the three month period prior to ejaculation2.
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.
Dr Andrew Povey, from the University of Manchester’s Institute of Population Health, said: “This research builds on our study of two years ago3 which looked at the risk factors associated with the number of swimming sperm (motile concentration) in men’s ejaculates.
