Three new studies presented at the annual conference of the American Society of Reproductive Medicine (ASRM) last week suggest that body weight, caffeine and cannabis can all affect a man's sperm. Caffeine 'perks up' sperm, by making it swim faster, while cannabis, despite its initial effect being similar to that of caffeine, causes sperm to 'lose stamina and burn out'. A third study shows that overweight men may have poorer quality sperm, causing reduced fertility.
Researchers from the University of Sao Paolo, Brazil, tested the sperm of 750 men, ranging from 'mild' coffee drinkers (one to three cups a day) to 'heavy' coffee drinkers (more than six cups per day). They found that all the sperm samples were of similar quality in terms of movement, concentration and hormone levels. But the sperm of men who drank coffee, compared with those who drank none, showed greater motility. The researchers believe that their study may indicate that caffeine-based compounds should be used in treatments for some male infertility.
In the second study, researchers from the State University of New York compared the sperm of 22 cannabis smokers and 59 fertile men who did not smoke cannabis. The study showed that smoking cannabis reduced both the semen volume and the total number of sperm produced by a man, and caused sperm cells to speed up temporarily, but lose energy very quickly. The scientists suggested that this initial burst of 'hyperactivity' would mean that sperm affected by cannabis would be less likely to be able to fertilise an egg. Dr Lani Burkman, leader of the research team, said 'the timing was all wrong'. In cannabis smokers, sperm became active 'too fast, too early'. Burkman said that the team had not precisely identified what caused this reaction in sperm, but she suggested that the active chemical in cannabis, THC (tetrahydrocannabinol), might cause improper sperm function either by direct stimulation or by 'bypassing natural inhibition mechanisms'.
A third study, presented by researchers at the Reproductive Biology Associates in Atlanta, Georgia looked at the effect of body weight on the genetic material of sperm cells. They compared the body mass index (BMI: weight in kilograms divided by the square of height in metres) with the quality of sperm DNA samples from 30 men. A person with a BMI over 25 is regarded as overweight, and over 30 as obese. 'As the BMI goes up, the DNA fragmentation rate goes up, and we could see a dramatic reduction of sperm quality' said team leader William Roudebush. The DNA fragmentation index (DFI) is also thought to increase in men over 50, and as a result of smoking, exposure to air pollution, prolonged abstinence or exposure of the testicles to excessive warmth. 'Typically, a male presenting with a DFI over 30 per cent will have reduced fertility and an increase of miscarriages' say the scientists.