DRINKING just five units of alcohol every week could reduce the quality of a man's sperm, new research suggests.

And 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. 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.

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.

"Our study suggests that even modest habitual alcohol consumption of more than five 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. "Young men should be advised to avoid habitual alcohol intake." The NHS recommends that men 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."