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

That is according to a study by Danish scientists published in the journal BMJ.

1,221 Danish men, aged 18 to 28, were recruited for the study when they attended a compulsory medical examination to determine their fitness for military service from 2008 to 2012.

It found that sperm concentration, total sperm count and the percentage of sperm with normal morphology were negatively affected with - what researchers call - increasing habitual alcohol intake.

"This association was observed in men reporting at least five units in a typical week but was most pronounced for men with a typical intake of more than 25 units per week", it says.

While men with a typical weekly intake above 40 units had a 33% reduction in sperm concentration compared to men with an intake of one to five units per week.

"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 study concludes.

It adds that young men should be advised to avoid habitual alcohol intake.

Professor Tina Kold Jensen is the lead author on the study. She told Newstalk Lunchtime that 'binging' did not play a big part.