Frequent visits to the sauna may lower men's sperm count, although the effect appears to be temporary, a new study finds.
In the study, healthy Finnish men in their 30s with normal sperm counts spent 15 minutes in a sauna two times a week for three months, after which they stopped visiting the sauna.
The sauna sessions lowered the men's sperm counts, and they remained below normal for three months after the men stopped visiting the sauna, compared with the levels at the study's start. After six months, however, sperm counts returned to normal.
The findings make sense, said Dr. Andrew Kramer, a urologist at the University of Maryland Medical Center, because higher temperatures are known to affect sperm production. "The testicles hang down from the body in men to cool them," Kramer, said. Men with undescended testicles can have impaired sperm product and fertility, according to the researchers.
During the sauna sessions, scrotal temperatures increased by 3 degrees Celsius (5.4 F)
However, the new study did not assess the men's fertility, so it's impossible to know whether their fertility was lower during the period they took saunas. A man's sperm count does not always correspond to his fertility, Kramer said.
Because of this, saunas can't be used as a method of birth control.
The study also found that sauna exposure affected the way DNA was packed into the sperm cells, and impaired the mitochondria, the cell's powerhouse. This might explain why sperm production is less efficient during sauna exposure, the researchers said.
"Avoidance of testicular heating and in particular of sauna exposure (in those countries where sauna is largely used) could be suggested in the counseling of males seeking fertility [treatment]," said study researcher Carlo Foresta, a professor of endocrinology at the University of Padova in Italy.
However, Kramer said the study doesn't provide enough evidence to say that healthy men shouldn't visit the sauna. The study was small, with just 10 people, so more research is needed to confirm the results.
Additional studies are also needed to look at the effects of sauna exposure on men whose fertility is already impaired, or on boys who haven't yet gone through puberty, Foresta said.
Previous studies have also suggested that frequent use of hot tubs, as well as sitting for long stretches with a laptop on the lap, can temporarily lower sperm count, according to the Mayo Clinic.
The study, conducted by researchers at the University of Padova in Italy, was published online Feb. 14 in the journal Human Reproduction.