As little as five alcoholic drinks a week could have an adverse effect on young men’s sperm quality, a study has found.
Researchers base their findings on a study into 1,221 Danish men between the ages of 18 and 28, all of whom underwent a medical examination to assess their fitness for compulsory military service between 2008 and 2012.
When they were tested, the men reported an average of 11 drinks in the past week.
Almost two-thirds (64%) had been binge drinking while around six out of 10 (59%) said they had been drunk more than twice in the past month.
The analysis showed that after taking account of various influential factors, there was no strong link between sperm quality and either recent alcohol consumption or binge drinking in the preceding month.
But drinking alcohol in the preceding week was linked to changes in reproductive hormone levels, with the effects increasingly more noticeable the higher the tally of alcoholic drinks.
Testosterone levels rose, while sex hormone binding globulin fell.
Almost half (45%, 553) of the men said that the quantity of alcohol they drank in the preceding week was typical of their weekly consumption.
And in this group the higher the tally of weekly drinks, the lower was the sperm quality, in terms of total sperm count and the proportion of sperm of normal size and shape.
The effects were evident from 5 or more units of alcohol a week upwards but most apparent among those who had 25 or more drinks every week.
And total sperm counts were 33% lower, and the proportion of normal-looking sperm 51% lower, among those knocking back 40 drinks a week compared with those drinking one to five.
The researchers say the findings could be the result of reverse causation where men with poor quality sperm have an unhealthier lifestyle and behaviours to start with.
But animal studies suggest that alcohol may have a direct impact on sperm quality, they say.