THURSDAY, Dec. 9, 2004 (HealthDayNews) -- Laptop computers pose a long-term threat to the fertility of young men who use them because they can reduce sperm formation by raising temperatures in the genital area, a small new study says.
Keep the laptop on a desk, not on the lap, is the advice of Dr. Yefim Sheynkin, an associate professor of urology at the State University of New York at Stony Brook and lead author of what is described as the first study of the effect of heat from the computers on the genital region.
But the warning drew a quick rebuttal from another fertility expert, Dr. Steven J. Sondheimer of the University of Pennsylvania, who said "it is not clear that it [the warming effect] is clinically important."
High scrotal temperature is "definitely a well-known risk factor for infertility," Sheynkin said. "We have known for years that it can affect male fertility and sperm production."
Men who are trying to become fathers are routinely advised to avoid saunas and hot baths, he said, and the new warning is "quite important because millions of young men and boys are using laptop computers on a regular basis now."
The study of 29 men in their 20s and 30s by the Stony Brook group found that keeping a laptop on the lap for an hour can raise scrotal temperatures by more than 2.5 degrees Celsius, enough to affect fertility significantly, said a report in the Dec. 9 issue of the European journal Human Reproduction.
But Sondheimer, a professor of obstetrics and gynecology, said there's little for men to worry about. "We've known for a long time that anything that warms the testicles lowers the sperm count, but whether this translates into infertility is not clear," he said. "Most likely it does not lead to infertility. We don't translate this information into clinical practice."
Previous studies have raised alarms about other factors that could affect male fertility by raising scrotal temperatures. French researchers reported in 2000 that driving a car for two hours raised the temperature by more than 2 degrees Celsius. A report from doctors in Kiel, Germany, that same year warned about the possible danger of plastic-lined disposable diapers, which were found to raise temperatures more than cotton diapers.
A 1999 study in the United States found that even seasonal temperature changes had a major effect on male fertility. Sperm production dropped by 41 percent in the summer as compared to winter, the study found, while sperm speed decreased and the number of defective sperm increased as the weather got hotter.
That effect was noted in the Cole Porter song Too Darn Hot, whose lyrics say in part, "According to the Kinsey Report, the average man you know, must prefer to play his favorite sport when the temperature is low."
The new study was "not designed to look at fertility issues," Sheynkin said, but merely to measure temperature effects. It found that the surface temperature of the Pentium 4 computers used in the study rose from 31 degrees Celsius (87 degrees Fahrenheit) to nearly 40 degrees Celsius (104 degrees Fahrenheit) after an hour of use.
Scrotal temperatures of the men rose by an average of 2.1 degrees Celsius when they sat with their thighs together to keep the computers centered. Temperatures went up more than 2.5 degrees Celsius when the computers sat on one leg or the other.
Many studies have shown that an increase of just 1 degree Celsius can affect sperm formation, Sheynkin said. Just 15 minutes of laptop use produced that temperature rise in the study.
If a user can't put the computer on a desk, laptop use should be limited to just a few minutes at a time, Sheynkin said. But even then, frequent laptop use can be damaging, he said.
"The effect of short-term exposure can be reversible," he said. "But if men don't give themselves time to recover, if they use laptop computers on a daily basis for years, it can take from three months to a year to recover. And the effect can be irreversible, which is very difficult to treat."
Sheynkin said he now plans a study to measure the physical effects of laptop use. "We will identify a group of men who are using laptop computers on a regular basis and see to what extent it affects fertility," he said.
An overview of male infertility can be found at the American Pregnancy Association.