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 journal Human Reproduction, recruited 2,249 men from 14 fertility clinics in the UK and asked them to fill out detailed questionnaires about their medical history and their lifestyle.
Men who produced ejaculates with less 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 younger than 30 years old, to have used cannabis in the three month period prior to ejaculation.
“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,” says Allan Pacey, a senior lecturer in andrology at the University of Sheffield and the study’s lead author.
“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.”
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 fertilize 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 that were not measured, such as the quality of the DNA contained in the sperm head.
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 supported the research.
*Image of “man lighting a cigarette” via Shutterstock