Last reviewed by Faculty of Harvard Medical School on January 24, 2013
By Harvey B. Simon, M.D.
Harvard Medical School
Every man who has put on an athletic supporter must have wondered why his "family jewels" are suspended in such a vulnerable position. Why hasn't nature tucked the testicles into the protective confines of the pelvis like their female counterparts, the ovaries?
The simple reason is temperature. Low temperature is essential for sperm production. But modern conveniences may warm things up or have other unintended effects on testicular function. Here's some interesting research that gives global warming a new meaning.
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Sperm and Temperature
Early in embryonic life, the testicles are positioned deep in the rear of the abdomen. But at about 17 weeks of pregnancy, the testicles begin to gradually descend through the abdomen. They arrive at the groin 5 to 10 weeks later and then cross into the scrotum by the 30th week of pregnancy.
Whether a man is hot or cool, his scrotal temperature averages about 6° F below his internal body temperature. When conditions are right, a young man's testicles can crank out up to 1,000 sperm a second. But at warmer scrotal temperatures, sperm production slows, sometimes impairing fertility.
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Both men and women have many good reasons to be up and around. But gents of reproductive age have extra motivation. Simply sitting in a car for two hours increases scrotal temperature by about 4° F. The effect is temporary, but men who average more than three hours a day driving take longer to father children than their peers who spend less time sitting in a car.
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A heated car seat feels mighty good on a wintry day, but can it add fuel to the fire of scrotal warming? To find out, doctors in Germany studied 30 healthy volunteers ages 20 to 53 who were dressed in boxer shorts, trousers and shirts during the experiment. Each man spent 90 minutes sitting on either a heated or unheated car seat while his scrotal temperature was recorded at one-minute intervals. Even sitting still on an unheated car seat boosted scrotal temperature, but the heated car seat added about 1° F without significantly increasing internal body temperature.
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Laptop computers are hot items so hot, in fact, that their internal operating temperatures top 158° F. Most men use their computers on a desk or table. But what if these marvelous devices are taken literally and used on a man's lap?
American scientists looked to answer the question by asking 29 healthy volunteers ages 21 to 35 to spend 60 minutes sitting with or without a working laptop perched on their thighs. The bottom surface of the laptop heated up to about 104° F by the end of the hour. Sure enough, scrotal temperatures rose by about 1° F more than with sitting alone.
These studies show that the heat generated by electrical devices that we take for granted can significantly increase scrotal temperatures. They also remind us that simply sitting still for an hour or longer can raise scrotal temperature, though to a lesser degree. These short-term experiments did not evaluate sperm counts, semen quality or fertility, but other investigations suggest that scrotal warming can have an adverse effect on fertility.
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"Calling" All Men
Another recent study suggests that "cool" devices like cell phones may also affect fertility.
Cell phones have revolutionized communication. Like many innovations, however, these devices have been greeted with concern as well as celebration. Because cell phones emit radiofrequency electromagnetic waves, they can interfere with some implanted cardiac pacemakers but only if the user holds the phone directly over the pacemaker. Similarly, cell phones have the potential to disrupt sensitive electronic monitoring devices in hospital intensive care units. Only a minority of monitors are vulnerable, and even then, only very close proximity between phone and monitor poses a risk.
Electromagnetic waves can also have biological effects. That's why some people worry that cell phones may cause cancer. Fortunately, many studies have failed to link cell phones to cancers of the brain, eye, salivary gland and the acoustic nerve in the ear. However, a 2008 study reported an association between cell phone use and benign tumors of the parotid gland, which is located beneath the lower jaw.
It's easy to see why scientists have wondered if cell phones might have ill effects on tissues in the head and neck. But researchers in Cleveland have asked quite a different question. Based on animal studies that indicate electromagnetic waves may damage testicular function, they wondered if cell phones might affect human sperm.
The researchers studied 361 men with an average age of 32 who were attending an infertility clinic. Men with medical problems known to effect sperm function were excluded from the study. Each man recorded his average daily cell phone use and submitted a semen sample, which was evaluated by technicians who did not have any knowledge of the subjects' cell phone use.
Forty men reported no cell phone use; 107 used cell phones for less than two hours a day; 100 men used cell phones two to four hours a day and 114 reported more than four hours of daily use. When the scientists analyzed the results, they found a steady decline in sperm count with increasing cell phone use. In addition, sperm structure, motility and viability all declined with increasing cell phone use.
It's only one study, and it did not account for possible electromagnetic wave exposure at work or for Bluetooth devices, computers or cell phone standby time. In addition, all the men were undergoing infertility evaluation. Still, it raises the interesting and worrisome possibility that new communication techniques may interfere with the outcome of old-style communications between men and women. Further studies are underway. And while you're holding the phone for additional results, please remember that cell phones do have one proven health risk: car crashes.
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The Bottom Line
Men who are having fertility problems might be wise to limit cell phone use and to avoid conditions that might boost their testicular temperatures.
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Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.