From hiking at high altitude to sleep apnea: research examines the impact on male fertility

Medical conditions that deprive the testicles of oxygen, such as sleep apnea, may contribute to the decline in male fertility seen over the past fifty years, a new study suggests.

Published in Nature Reviews Urologythe literary judgement examines how factors such as sleep apnea, varicocele, and exposure to high altitude affect sperm quality and overall reproductive health in men.

The review was led by reproductive biologist Dr. Tessa Lord, Senior Lecturer at Newcastle University and member of HMRI’s Infertility and Reproduction Research Programme.

“Medical conditions such as varicocele and sleep apnea reduce the level of oxygen-rich blood in the testis – a phenomenon known as testicular hypoxia,” said Dr. Lord.

“We know from existing research that testicular hypoxia can negatively impact sperm count and quality by disrupting hormone production and gene expression.”

Findings indicate a long-term threat to fertility

The review examined findings from multiple studies to holistically capture the causes and effects of testicular hypoxia in different scenarios.

Dr. Lord said that when a lack of oxygen to the testicles is caused by chronic medical conditions – such as sleep apnea or varicocele – there is a persistent threat to reproductive health.

“Varicocele, or enlarged veins in the scrotum, is a common abnormality diagnosed as the cause of infertility in up to 45% of men who have difficulty conceiving,” said Dr. Lord.

“Obstructive sleep apnea is the most common sleep-related breathing disorder. It affects 13% to 30% of the male population, and that number is increasing, with obesity being a major risk factor.”

Several studies have shown a link between sleep apnea and infertility in men, but Dr. Lord said we urgently need further research to understand the direct effects on sperm production and quality.

Dr. Lord explained that while high-altitude activities such as hiking can cause testicular oxygen deprivation, or hypoxia, the effects on fertility are usually only temporary.

“The good news for hikers is that reduced fertility at high altitude is generally reversible once oxygen is restored to the body.

“However, this may take a few months to resolve, following their return to ‘sea level’,” said Dr. Lord.

Dr. Lord calls for greater public and clinical awareness of the reproductive risks associated with persistent testicular hypoxia.

“Treating conditions such as varicocele and sleep apnea early could help reduce associated fertility risks. There is promising evidence that subfertility caused by hypoxia can potentially be reversed if the underlying problem is addressed,” said Dr. Lord.

In men, infertility is defined as the inability to become pregnant after 12 months or more of regular unprotected intercourse, while subfertility represents a less serious impact that may nevertheless reduce the chance of conception.

There is an urgent need to uncover intergenerational effects

The increase in the prevalence of conditions such as sleep apnea, combined with possible intergenerational effects, makes testicular hypoxia a critical issue in understanding male fertility trends.

“We know that male fertility has declined significantly over the past 50 years,” said Dr. Lord. “Emerging evidence suggests that testicular hypoxia in fathers could result in embryos with developmental problems, and that those children could grow up to experience fertility problems themselves.”

Despite advances in understanding the relationship between hypoxia and fertility, Dr. Lord that there are still significant knowledge gaps in science.

“We don’t have all the answers yet, especially when it comes to the impact on sperm quality when testicular oxygen deprivation occurs. Also, more research is needed to understand the full extent of the generational impact.”

Dr. Lord emphasized that further research is needed to fully understand the broader implications of these findings and develop effective interventions.

“We need to improve fertility outcomes today and also help protect the reproductive health of future generations,” said Dr. Lord.