CohortHumann = 102013

Seminal and molecular evidence that sauna exposure affects human spermatogenesis.

Journal: Human reproduction (Oxford, England)Published: 2013DOI: 10.1093/humrep/det020

Plain-language summary

This study set out to see how regular sauna use affects sperm health in men whose sperm counts were normal to begin with. Ten men used a Finnish sauna twice a week for 3 months, each session 15 minutes at 80 to 90 degrees Celsius, which is 176 to 194 degrees Fahrenheit. The researchers measured sperm count, movement, DNA packaging and heat-related gene activity before, during and after. Sauna use lowered sperm count, movement and DNA packaging, and every measure was back to normal within 6 months of stopping.

Key findings

Two sauna sessions a week for 3 months at 80 to 90 degrees Celsius, which is 176 to 194 degrees Fahrenheit, lowered sperm count and movement clearly.
Sperm DNA packaging and the sperm's energy-producing machinery also got worse during the sauna period.
Genes the body switches on in response to heat and to low oxygen became more active.
Sex hormones did not change at all, so the effect was on the sperm rather than on the hormones driving them.
Every sperm measure returned to normal within 6 months of the last session.

How to analyze the study yourself

Study type: A longitudinal study tracks the same people over time, which helps spot changes linked to an exposure like sauna use, but without a comparison group, it cannot rule out other factors that might have affected the results.
Population: 10 men whose sperm counts were normal before they started. No men with poor sperm health were included.
Funding: No external funding was sought and the authors declare no conflict of interest.
Takeaway: This study found that using a sauna twice a week for three months at 176 to 194 degrees Fahrenheit lowered sperm count, movement and DNA packaging in men whose counts started normal, left their hormones untouched, and that every measure was back to baseline within six months of stopping. If you are trying to conceive, it may be worth pausing regular sauna while you are trying, and if you have already been going, the effect reverses.