Hot baths, hot tubs or whirlpool baths may make a man feel good, but they may harm his fertility, according to a new University of California San Francisco study reported in the January-February 2007 issue of “International Braz J. Urol,” the official journal of the Brazilian Society of Urology.

The study of a small group of infertile men led by Paul J. Turek, MD, a professor in the UCSF Department of Urology and director of the UCSF Male Reproductive Health Center and colleagues showed cessation of exposure to wet heat can drastically increase total motile sperm account, the effect lasting beyond three months in 45% of infertile men, indicating that the affected sperm production was reversible.

“It has been believed for decades that wet heat exposure is bad for fertility, as an old wives’ tale, but this effect has rarely been documented,” said Turek. “We now have actual evidence to show patients that these recreational activities are a real risk factor for male infertility.”

Early studies showed that testicular hyperthermia has a deleterious effect on male fertility and is recognized as a cause of impaired male sperm production.   The harmful effect of heat has been well observed both in animals and humans.   Studies showed heat generated either exogenously or endogenously decreases sperm concentration, impairs motility and reduces the number of morphologically normal sperm.

Most studies done so far only considered the effect of dry heat, but not wet heat on spermatogenesis. The only study of wet heat was conducted in 1965, according to the researchers of the current study. In that early study, a decline in sperm production was observed in 20 oligospermic men after they were exposed to wet heat with a bottle at 43 to 45 ^o C held between the thighs for 30 minutes on 6 alternating days. An improvement in sperm quality was observed after the men stopped web heat exposure.   But the data on sperm quality before and after heat exposure was not provided by the authors.

In the current study, Paul J. Turek and colleagues wanted to know the effect of the common web heat media such as with hot tubs, Jacuzzis, or hot baths on the sperm quality of infertile men.

The 3-year study involved 11 men at average age 36.5 years with eight men diagnosed with infertility who had tried to impregnate their female sexual partners during the two and half years before being enrolled in the study.   Sperm quality including ejaculate volume, sperm concentration, motility and total sperm count of each man was evaluated at the beginning and during the course of the study.

To be eligible as a participant, men should have been subject to wet heat exposure with their bodies immersed in a hot tub, heated Jacuzzi or bath at a temperature warmer than body temperature for at least 30 minutes per week for at least three months before entering the study.

The men were also surveyed for their exposure to wet heat in terms of the type, frequency, duration/episode and overall length.   On average, these men were exposed to wet heat for 149 minutes per week, ranging from 60 to 315 minutes, with a mean total duration of web heat exposure of 2.9 years.   Five men were exposed to hot baths, four to both hot baths and hot tubs, and two to Jacuzzi.

Three to six months after the men stopped exposure to wet heat, five men or 45% increased their total motile sperm counts (TMC) by at least 200% although in the entire cohort, increase in TMC was not statistically significant.   Among those five men, the mean increase in TMC was 490%.

The remaining six men did not experience an increase in sperm count or motility. The researchers said it's likely these men were affected by their smoking habits.   Among these men, five were chronic tobacco users compared to only three occasional smokers in the responder group.

The researchers concluded that frequent exposure to wet heat in the form of hot tubs, Jacuzzis, or hot baths could impair sperm production and sperm motility and cessation of such exposure can reverse the lower sperm quality, mostly in sperm motility and improve some men's fertility.

An estimated 7 % of American couple is unable to conceive a child naturally within a year.   Men are solely or in part responsible for about 70% of the cases, according to the 2002 National Survey of Family Growth and the American Society for Reproductive Medicine.

The majority of infertility cases can be effectively treated with drugs and or surgical procedures.   But “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,” Turek said.

Turek advises men who would like to father a child to “treat your body like a temple: Eat well, sleep well and take good care of yourself.”