High-Altitude Hiking Linked To Decline In Fertility Among Men: Study

High-altitude hiking, sleep apnoea and other conditions which deprive a man's testes of oxygen, could be contributing to a decline in fertility over the past 50 years, a new study has suggested.

The review article, published in the journal Nature Reviews Urology, explored how exposure to low oxygen levels can impact sperm quality and overall reproductive health of men, revealing that 'testis hypoxia' could be critical to declining male fertility.

Infertility in men refers to an inability to achieve pregnancy after at least 12 months of regular unprotected sexual intercourse, while sub-fertility represents a less severe situation, whereby one's chances of conceiving are lowered.

A lack of oxygen in the testes, or testis hypoxia, caused by chronic medical conditions -- such as sleep apnoea or varicocele -- can be a sustained threat to reproductive health, lead author, Tessa Lord, a reproductive biologist and senior lecturer at The University of Newcastle, Australia, explained.

"Varicocele, or enlarged veins in the scrotum, is a common abnormality which is diagnosed as the cause of infertility in up to 45 per cent of men who are struggling to conceive," Lord said.

Obstructive sleep apnoea is a common disorder, in which muscles in the throat narrow the airway during sleep, thereby affecting one's breathing and blood oxygen levels. Cases have been shown to increase, with obesity being a key risk factor.

"Multiple conditions can cause hypoxia in the testis, including exposure to high altitude, sleep apnoea, testicular torsion and varicocele," the author wrote.

"We know from existing research that testis hypoxia can negatively impact sperm count and quality by disrupting hormone production and gene expression," Lord said.

Further, while high-altitude activities such as hiking can cause a lack of oxygen in the testes, the effects on fertility are short-term, but can still take a few months to resolve after returning to 'sea-level', Lord said.

The author added that while short-term and long-term exposures to hypoxia have been shown to have detrimental effects on sperm, downstream effects on embryo development and offspring health are less well understood.

Therefore, testis hypoxia is critical for understanding the significant decline in male fertility over the past 50 years.

"Emerging evidence suggests that testis hypoxia in fathers could result in embryos with developmental issues, and those children could grow up to experience fertility issues themselves," Lord said.

However, significant knowledge gaps in science remain, for which more research is needed, the author said.

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