Beware men, especially if you plan to father a child soon. A new research has now linked alcohol consumption to poor quality of sperm.

According to the new study, drinking just five units of alcohol every week could reduce the quality of sperm in healthy young men.

The study is based on the findings on 1,221 Danish men between the ages of 18 and 28, all of whom underwent a medical examination to assess their fitness for military service between 2008 and 2012.

As part of their assessment, the military recruits were asked about their drinking habits. They were also asked to provide a semen sample to check on the quality of their sperm, and a blood sample to check on their levels of reproductive hormones.

The average number of units drunk in the preceding week was 11. Almost two thirds (64 per cent) had binge drunk, while around six out of 10 (59 per cent) said they had been drunk more than twice, during the preceding month.

Researchers found that 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 units.

Testosterone levels rose, while sex hormone binding globulin (SHBG) fell; similar associations were also evident for the number of times an individual had been drunk or had binge drunk in the preceding month, researchers said.

Almost half (45 per cent, 553) of the men said that the quantity of alcohol they drank in the preceding week was typical of their weekly consumption.

They also found that the higher the tally of weekly units, the lower was the sperm quality, in terms of total sperm count and the proportion of sperm that were of normal size and shape.

The effects were evident from five plus units a week upwards, but most apparent among those who drank 25 or more units every week.

Heavier drinkers (50 units a week) had 33 per cent lower sperm count and also had 51 per cent less normal-looking sperm than those who drank fewer than five units per week, found the study.

The research has been published in the journal BMJ Open.