Drinking just five units of alcohol every week could reduce the quality of a man’s sperm, new research suggests.
The more alcohol consumed, the weaker the quality of the sperm, the study found.
Men of a reproductive age should be advised to steer clear of habitual drinking, the authors said.
The study, published in the journal BMJ Open, examined 1,200 Danish male military recruits between the ages of 18 and 28, all of whom underwent a medical examination between 2008 and 2012.
As part of the assessment they were asked about their drinking habits and invited to provide sperm and blood samples.
The average number of units drunk in the preceding week was 11.
They found that drinking alcohol in the previous week was linked to changes in reproductive hormone levels, with the effects increasingly noticeable the more alcohol consumed.
Testosterone levels rose while sex hormone binding globulin (SHBG) fell, they found.
Almost half said the quantity of alcohol drunk in the preceding week was typical of their normal weekly consumption.
Among this group of men, researchers found that the higher the tally of weekly units, the lower was the sperm quality in terms of sperm count and the proportion of sperm that were of normal size and shape.
The effects were evident in those who drank five or more units a week and most apparent in those who drank 25 units or more.
Those who typically drank 40 units a week had 33% lower sperm count and also had less “normal looking” sperm than men who drank between one and five units a week.
“Our study suggests that even modest habitual alcohol consumption of more than 5 units per week had adverse effects on semen quality although most pronounced associations were seen in men who consumed more than 25 units per week,” the authors wrote.
” Alcohol consumption was also linked to changes in testosterone and SHBG levels. Young men should be advised to avoid habitual alcohol intake.”
The NHS recommends that m en should not regularly drink more than three to four units of alcohol a day.
Commenting on the study, Professor Chris Barratt, professor of reproductive medicine at the University of Dundee, said: ” I think the main message of this paper is clear – high levels of alcohol intake do appear to be associated with changes in sperm and semen that may affect fertility.
“But it is interesting to note that men who didn’t drink any alcohol at all also had reduced semen quality – this was not commented on in the paper but needs further research.”
Dr Allan Pacey, senior lecturer in andrology at the University of Sheffield, added: “Men and their partners who are trying to start a family are understandably concerned to know if aspects of their lifestyle are detrimental to sperm production and male fertility.
“However, with regard to alcohol consumption and semen quality the data has been conflicting, with some reports suggesting evidence of harm and others showing no effect. As far as I am aware, we also don’t currently know by what biological mechanism alcohol consumption could reduce semen quality, so more research is needed.”