Sleep problems can drastically lower the fertility among young men, a study has warned.

Scientists at the University of Southern Denmark examined nearly 1,000 men in their late teens or early 20s about to do military service gave sperm samples and answered questions about how well they slept.
Questions included how often the men slept badly and how often they found it difficult to nod off.

They were also asked if they woke up regularly during the night and if they found it difficult to go back to sleep.

The study found that those who frequently retired late, woke many times in the night or struggled to nod off in the first place; had a sperm count 25 per cent lower than those who had no trouble, News.com.au reported.

The report said that the frequency of sleep disturbances increased in the industrialised world during the past few decades, a period in which a decline in semen quality has also been reported.

The researchers explained that the men who sleep less tend to have unhealthier lifestyles and weigh more, drink more alcohol and were more often smokers.

The study has been published in the American Journal of Epidemiology.