Research has demonstrated for the first time that recreational immersion in hot water impairs male fertility. Even though the study was small, the investigators say the findings should be shared with all hopeful fathers.

The study’s 11 infertile patients (mean age 36) agreed to stop their habitual use of hot tubs or heated Jacuzzis. When tested three months later, five of the men showed a mean fivefold jump in total motile sperm counts. Five of the six nonresponders were heavy smokers. “Even though this is a small study, it provides enough evidence to comfortably recommend that men seeking to procreate should avoid hot-water immersion,” says urologist Paul Turek, MD, the lead investigator and a fertility specialist at the University of California, San Francisco. “The study took three years because very few patients met the strict criteria. The population is small to begin with, and concurrent female or male fertility treatments were not allowed, and female evaluation had to be unremarkable. We also needed time for adequate follow-up.” The findings were reported in the International Brazil Journal of Urology (2007;33:50-57).

Dr. Turek said that in a 1965 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, but there were no details on semen quality before and after the study. 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 added.

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