Immersion in hot water decreases sperm counts and motility, but the effect is reversible

Researchers have demonstrated for the first time that immersion in hot water adversely affects male fertility.

Results from a three-year study analyzing data from infertile men who had been repeatedly exposed to high water temperatures indicate that there is indeed a direct link to impaired sperm production and motility. The researchers say clinicians should now add hot baths and hot tubs to the list of “things to avoid” when men attempt to conceive.

The negative effect of hot water exposure was reversed in 45% of the infertile men who discontinued the practice for three months, the study said.

For decades, some people have argued, with little evidence, that wet heat exposure impairs fertility, but the contention was considered “an old wives’ tale,” said lead investigator Paul Turek, MD, professor of urology and director of the University of California in San Francisco Male Reproductive Health Center. “We now have evidence that these recreational activities are a real risk factor for male fertility.”

Dry heat exposure such as fevers or applied external heat is a well-documented cause of impaired sperm production in both animals and humans, he noted.

The study’s 11 infertile men (mean age 36.5 years, range 31-44 years) were identified on the basis of repeated exposure to wet heat and were asked to cease that exposure for three or more months. Five of the patients (45%) responded favorably to the change and had a mean fivefold increase in total motile sperm counts after three to six months. This increase was largely driven by a significant increase in sperm motility among responders, from a mean of 12% at the start of the study to 34% post-intervention.

Among the six patients who did not have an increase in sperm count or motility, tobacco use emerged as a possible confounding factor. Five of the six men who were non-responders were chronic tobacco users with a significant smoking history, in contrast to only three occasional smokers in the responder group.

Among the non-responders, there was a mean of 5.6 pack-years of smoking compared with just 0.11 pack-years among responders. The prevalence of varicoceles was similar in both responders and non-responders. No other potential gonadotoxic factors were identified.

The findings should be of particular interest to urologists and their infertile male patients because it confirms that the toxic effect of hyperthermia on semen quality may be reversible in some men, Dr. Turek said. He and his colleagues reported the findings in the International Brazil Journal of Urology (2007;33:50-57).

In select patients, recommending cessation of hot water immersion could change infertility treatment from in vitro fertilization to intrauterine in-semination (IUI) or from IUI to natural pregnancy. “One implication of this work is that a simple lifestyle maneuver could ‘shift the care’ from high-tech intervention to low-tech or no-tech,” Dr. Turek said. “Couples really prefer having kids at home and not with technology.”

For this study, wet heat exposure was defined as the immersion of the body in a hot tub, heated Jacuzzi, or bath at a temperature warmer than that of the body for 30 minutes or more per week for at least three months prior to the study. Men were excluded from the study if they had received infertility treatments in the previous 12 months or if female infertility was a coexisting factor.

Dr. Turek said the only previously published study to examine this association was performed in 1965. In that study, 20 men were exposed to direct scrotal wet heat for 30 minutes on six alternating days. The findings showed a temporary decline in sperm production during the exposures, but there were no details on semen quality before and after the study. An unpublished Swiss study in the 1940s had also linked wet heat to temporary male infertility.

“It is generally known that men should avoid these exposures, but now we finally have data to say that total-body wet heat exposure can impair fertility potential. Even though this is a small study, there is enough evidence in it to comfortably make a recommendation,” Dr. Turek told Renal & Urology News. “This study took several years to do because very few patients met all the strict criteria for inclusion. For example, the population may be small to begin with, and concurrent female or male fertility treatments were not allowed and fe-male evaluation had to be unremarkable. We also needed time for adequate follow-up.”