What mountain climbing does to your sperm

Thinking about taking a romantic excursion up in the mountains? If you’re trying to get pregnant, this may not be the best strategy. A study published in the Journal of Assisted Reproduction and Genetics has linked being at high altitudes with low sperm DNA quality. 

Why did they choose focus on high altitudes? Previous research had shown that men who regularly go on high altitude mountaineering excursions had lower sperm count than men who didn’t. Their swimmers didn’t swim too fast, either.

Other studies have linked hypoxia to infertility in rats, monkeys, and men. Because the air up there has less oxygen in it, hanging out at high altitudes leads to hypoxia.

The missing link? Why does hypoxia cause problems with male fertility?Researchers Yuqi Gao and colleagues collected semen samples from men in three groups: those who live at low altitudes (1,400m), those who had been at high altitude (5,300m) for only 1 month, and those who had been at the high altitude for a year.

They then looked at two markers for sperm integrity. First, they wanted to know how many mitochondria were in each sperm cell. Mitochondria are the cell’s energy factory; they turn sugar into energy through a chemical reaction that relies on oxygen. So, the less oxygen you have, the more mitochondria you might need to get the job done. This is especially true if you’re a sperm. Sperm need all the energy they can get to swim through the harsh female interior.

They measured the relative amount of mitochondrial DNA in the sperm from these men. Men who had been at high altitudes for a short time (1 month) had 5 times more mitochondria in their sperm than men who lived at a low altitude. But, after living up high for about a year, that number (while still higher than the low altitude guys) was much lower.

What about the quality of the DNA, though? They found no defects in the mitochondrial DNA of any of the men in the study. However, nuclear DNA (you know, the regular DNA), was compromised in men that lived at high altitudes. Men who had been at high altitudes for a month had the lowest quality DNA, meaning it had suffered more damage. Men who had been up there for a year had higher quality DNA, but it was still slightly worse than the guys who lived closer to sea level.

Unfortunately, this study didn’t look at sperm motility or fertilizing potential, which would have tied all the studies together very nicely. But it’s something to think about next time you’re mountain climbing.

Luo Y, Liao W, Chen Y, Cui J, Liu F, Jiang C, Gao W, & Gao Y (2011). Altitude can alter the mtDNA copy number and nDNA integrity in sperm. Journal of assisted reproduction and genetics PMID: 21909897

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