Men who smoke marijuana risk the size and the shape of their sperm, a study by researchers at the Universities of Sheffield and Manchester suggests.
The study, conducted on 2,249 men, also found that quality of sperm goes down in the summers and men who do not have sex for more than six days have better sperm shape and size (sperm morphology).
For the study, the researchers studied the medical history and lifestyle of 1,970 participants from 14 fertility clinics across the U.K.
Researchers then compared the 318 men who produced less than 4 percent sperm with the correct size and shape to a control group of 1,652 men who produced normal sperm morphology.
The study findings revealed that men who ejaculated less than 4 percent of normal sperm were nearly twice likely to have given a sample during the summers, or to have used marijuana in the three months prior to submitting the sample.
"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," lead author Dr Allan Pacey, senior lecturer in Andrology at the University of Sheffield, said in a press release.
Apart from side effects of marijuana on sperm quality, the researchers also found that men exposed to paint strippers and lead have risk of producing sperms with poor morphology, Professor Nicola Cherry, a part of the study, said.
Dr Andrew Povey of the University of Manchester's Institute of Population Health said the current study was based on research done two years ago. It focused on risk factors linked to the number of swimming sperm (motile concentration) during ejaculation.
He explained that the previous research found that there were relatively fewer 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 will improve their chances of a conception," Povey said.
A recent study showed that psychological stress has harmful effects on the sperm quality.
The findings of the current study were published in the 'Journal of Occupational and Environmental Medicine'.
