MONDAY, Oct. 15, 2001 (HealthDayNews) -- Electric blankets have been a focus for years when talk turns to harmful electromagnetic fields in the house, but now research shows that it's the rest of the bedroom scientists should have been looking at.
The study says modern electric blankets are safe, but exposure to electromagnetic fields elsewhere in bedrooms or from nearby high-voltage power lines may reduce the nighttime production of the hormone melatonin for certain women. And, some scientists theorize that reduced melatonin levels may be linked to an increased risk of breast cancer.
An estimated 192,200 American women will be diagnosed with breast cancer this year, and about 40,600 will die of the disease, making it the second-leading cause of cancer deaths in women after lung cancer.
Two studies reported in American Journal of Epidemiology this month examine the effects of electric and magnetic fields on levels of melatonin in women.
Scott Davis, lead author of one study, is the chairman of epidemiology at the University of Washington School of Public Health and Community Medicine in Seattle, Wash. Davis' team was one of the first to investigate links between electromagnetic fields and cancer, particularly leukemia.
"In the late 1980s and early 1990s, we began to take note of a building body of evidence that suggested that magnetic fields and other factors might be capable of affecting the normal functioning of the pineal gland," says Davis. The gland, located in the base of the brain, produces melatonin, a hormone whose production is prompted by light exposure.
The evidence suggested that interfering with the production of melatonin could affect the release of certain reproductive hormones, which might be related to the risk of breast cancer, he says. "All of this sounded very plausible based on laboratory studies, but nobody had ever really looked in humans to see whether or not magnetic fields of the type you're normally exposed to in the home could actually effect hormone production."
The latest study focused on the potential link in a human population, says Davis. The researchers examined 203 women in Washington state between 1994 and 1996. Each woman filled out a questionnaire and provided urine samples for a 72-hour period at two different times of the year.
The surveys included the women's medical histories and electric-blanket use. During the 72-hour experiments, equipment monitored magnetic field levels and how much light came into the women's bedrooms. The nighttime urine samples measured concentrations of 6-sulfatoxymelatonin, an indication of nighttime body melatonin levels.
Not surprisingly, the team found that the numbers of hours of darkness, which varied from season to season, had the most marked effect on melatonin levels.
Davis and his colleagues also found a relationship between reduced melatonin levels and alcohol consumption and the use of certain prescription medications, such as beta blockers, calcium channel blockers and psychotropic drugs. Along with increasing age and weight, use of those substances have been linked to reduced melatonin production in other studies.
But after adjusting for those factors, researchers found that bedroom magnetic field levels, at a frequency of 60 Hertz, also were linked to lower nighttime melatonin levels. The team found no relation between electric blanket use and melatonin levels.
"Electric blankets were pretty effectively re-engineered a number of years ago," says Davis. "Modern-day electric blankets -- anything you buy in the store now -- [has a different] configuration of the heating elements in the blanket so that it doesn't produce any magnetic fields."
"In the last several years, that exposure source has basically disappeared, unless you have a really old blanket," he says.
In the second study, researchers from Quebec and France compared melatonin levels in 221 women living close to high-voltage power lines and 195 women living far away from the lines. The women lived in Quebec City, where electricity is carried by 735,000-volt power lines, which produce magnetic fields well below Canada's standard safety limits.
Overall, living closer to the power lines had no impact on melatonin levels, except for older women and heavier women. "But we're not sure of this effect because we had so few people in those groups," says study leader Dr. Patrick Levallois, scientific advisor for the National Institute of Public Health of Quebec. He says he would like to study the effect on this group in greater detail.
"If there is an effect on melatonin, that would be a demonstration that what is considered a safe level [of exposure from power lines] is not without any effects," he says.
"Some studies done in laboratories have demonstrated that melatonin is a very powerful antioxidant. There is some data which could explain a possible protective effect of melatonin on cancer and other health-related problems," he says.
However, until more data is available, both Levallois and Davis say people don't need to do anything different.
Davis says, "This demonstrated for the first time in a population setting
that exposure to magnetic fields at the levels and of the types that generally are found in the home, can actually have an observable effect on the production of a hormone that we think is important in regulating a whole series of hormones in the body, including reproductive hormones of interest to breast cancer."
"That's not to say that we've established that magnetic fields cause breast cancer -- far from it," says Davis.
Davis says future studies should look at whether women with a genetic predisposition for breast cancer should be more concerned about magnetic field exposures. "Some of our findings suggest to us that there may be particular subgroups of women that might be more susceptible. Clearly, one potential subgroup to think about is one that is different genetically in a way that would already place one at higher risk of breast cancer."
What To Do
The National Institute of Environmental Health Sciences publishes a fact sheet on electric and magnetic fields, and the National Cancer Institute provides background information on magnetic field exposure.
You can also check this Web page on power lines and human health from the Medical College of Wisconsin.
For information about breast cancer, visit the American Cancer Society.
