Sleep problems can drastically lower the fertility of young men, warns a study.
Those struggling to make it through the night have more problems than those enjoying a sound rest. Their sperm counts were cut by a quarter and they also had smaller testicles.
The latest research is the first to look specifically at whether broken rest affects male fertility although links between sleep and health have been well-studied.
Sperm numbers dropped by more than a quarter in men not getting a full night's rest due to late nights, insomnia and broken sleep
Sperm counts have been tumbling in recent years amid fears that male fertility is being harmed by poor diet and lifestyle or even ‘gender-bending’ chemicals in the environment.
But work at the University of Southern Denmark suggests that modern sleep patterns may also be a factor.
The scientists examined nearly 1,000 men in their late teens or early 20s about to do military service. They gave sperm samples and answered questions about how well they slept.
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Questions included how often they slept badly and how often they found it difficult to nod off. The men were also asked if they regularly woke up during the night and found it difficult to go back to sleep.
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.
Tests showed that their testicles were also significantly smaller, according to the study published in the American Journal of Epidemiology.
A lack of sleep even made their testicles shrink, the study found
It said: ‘The frequency of sleep disturbances has increased in the industrialised world during the past few decades, a period in which a decline in semen quality has also been reported.
‘The results may have important public health implications.’ They added that it was not clear why sleep problems affected sperm levels and that it had not been proven that one caused the other.
The researchers stressed that men who sleep less tend to have unhealthier lifestyles. They weighed more, drank more alcohol and were more often smokers.
It was also possible sleep problems affect levels of testosterone. At least one other study has found keeping young men awake for longer reduces production of the sex hormone.
The report said: ‘This is the first study to relate sleep disturbances to semen quality. Men with a poor sleep score had poorer semen quality and smaller testicles.’
Experts believe the ideal amount of rest is seven to eight hours a night. But the average Briton sleeps for six hours and seven minutes.
A British male fertility expert said that although the study was interesting, men should not worry.
Dr Allan Pacey, from Sheffield University, said it was unlikely that the poor sleepers would have suffered a major impact on their fertility.