Sleep Apnea Linked to Weaker Sperm Movement, and CPAP Use Brought Gains

Men with untreated obstructive sleep apnea had lower semen volume and fewer sperm that swim well than healthy men, according to a small study reported by ScienceAlert. Among a subset of participants who used a CPAP machine, sperm movement improved within a month.

The study is small, and the CPAP treatment was not randomized, so it cannot show that treating sleep apnea restores fertility. The findings were published in the journal Sleep Medicine.

What did the researchers compare?

A team led by researchers at the University of Hong Kong–Shenzhen Hospital in China compared 72 reproductive-aged men with untreated sleep apnea to 22 healthy controls. Participants were aged 18 to 50, and the men with sleep apnea were diagnosed with an overnight test at a sleep center.

The men with sleep apnea had significantly lower semen volume. Their semen also had fewer sperm capable of swimming forward and higher levels of several inflammatory markers. The sleep apnea group had roughly 10% fewer sperm that could swim forward and 10% fewer that could swim at all.

Did sleep apnea affect erectile function?

Not in this study. The researchers found that sleep apnea was not associated with erectile dysfunction, but it was associated with poorer semen quality, independent of erectile function. Earlier observational studies had linked sleep apnea to a higher risk of erectile dysfunction, while evidence on sperm has been scarce, ScienceAlert reported.

What happened when men used CPAP?

Twenty-five participants used a CPAP machine regularly, meaning four hours or more per night on five or more nights a week. One month later, the share of progressively motile sperm, meaning sperm that swim forward, rose from nearly 40% to 45%. The four elevated inflammatory markers did not show significant reductions at that point.

Keeping people in the trial proved hard. At three months, 15 men were still using the machine and reporting for follow-up. By six months, only 8 remained. ScienceAlert noted that CPAP machines can be clunky and uncomfortable, and that many patients struggle to keep using them. Among those who stayed with treatment, sperm motility remained above its starting level, but the authors cautioned against reading too much into that given the tiny sample.

Why does it matter?

Obstructive sleep apnea, in which the airway narrows during sleep and causes loud snoring interrupted by pauses in breathing, affects about a quarter of all men over the age of 30, according to the report. It is also tied to high blood pressure and other cardiovascular problems. The new work adds a possible reproductive angle to a condition many people think of mainly as a sleep or heart issue.

The study does not show whether the differences affect a man's ability to conceive. The authors describe the measures they tracked as “key determinants of male reproductive potential,” but ScienceAlert noted the effect on conception may or may not be significant.

The authors suggest that checking for sleep-disordered breathing could be considered an exploratory step for men whose semen abnormalities have no clear cause. That echoes a 2025 correspondence in Nature Reviews Urology, in which urologists in Brazil argued that sleep medicine should be part of routine evaluation for male infertility.

How solid is the evidence?

It is early. The study was prospective but small, treatment was not randomized, and most CPAP users dropped out before the six-month mark, which makes long-term results hard to judge. The group of 25 CPAP users was also much smaller than the 72 men with sleep apnea overall.

The authors say their work addresses a knowledge gap that has been largely unexplored. They propose a model in which disrupted breathing during sleep and inflammation in the semen environment are jointly associated with impaired sperm function. Animal studies and some observational human studies had previously suggested that low oxygen or body-wide inflammation from sleep apnea could interfere with sperm production, according to ScienceAlert.

What comes next?

The team is calling for larger studies to clarify the precise molecular mechanisms and to confirm whether CPAP treatment brings long-term fertility benefits.

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Around Prague, based on reporting by ScienceAlert