Non-ionizing Radiation (Electromagnetic Fields)

Overview and Mechanisms

Electromagnetic waves are a type of non-ionizing radiation, i.e., a type of low-frequency radiation without enough energy to break off electrons from their orbits around atoms and ionize (charge) the atoms. Microwaves, radio waves, radar and radiation produced by electrical transmission are examples of radiation sources that generate electromagnetic fields (EMF). Electric lighting generates electromagnetic fields. Fluorescent lighting and many types of low-voltage lighting produce fields that are particularly high compared to incandescent lighting. In addition, computers and many other types of wired and wireless electronic equipment (e.g., cell phones) all create electromagnetic fields of varying strengths.

IARC has classified EMF as possible human carcinogens based on the scientific literature related to EMF and childhood leukemias. In 1998, a National Institute of Environmental Health Sciences (NIEHS) EMF Working Group recommended that low-frequency EMF, such as those from power lines and electrical appliances, be classified as possible human carcinogens, again primarily based on evidence related to childhood leukemias. However, consensus has been more difficult to reach about the relationship between EMF and breast cancer.

Exposure levels of EMF have increased exponentially in the past two decades due to the widespread use and deployment of wired and wireless technologies, including city-wide Wi-Fi networks in the United States and Europe. Everyone in industrialized countries is exposed to EMF from multiple sources every day, and many of these exposures are involuntary.

Despite rising exposure levels, there has been little U.S. federally funded research on the possible health effects of EMF in nearly a decade. Fortunately, research has continued internationally, and the results are troubling to scientists and the public about possible health effects. In August 2007, an international team of respected scientists released a summary analysis of the science on EMF and potential health concerns, including breast cancer and other cancers as well as neurodegenerative diseases and disorders. Called The BioInitiative Report, it is based on a review of more than 2,000 studies. It calls for stronger safety standards on EMF exposure to prevent future cancers and other diseases and disorders. This report was endorsed by the European Environmental Agency.

Evidence Linking Non-Ionizing Radiation and Breast Cancer Risk

Although not all epidemiological or occupational studies have found significant relationships between exposures to EMF and risk for breast cancer, many have found these effects. Methodological issues may account for some of the discrepancies, given the relatively small (but still statistically significant, and important in real lives) effects that are found and the ubiquitous nature of background EMF in our daily lives.

A recent population-based case-control study in the United States looked at breast cancer risk in women who were exposed occupationally to low, medium or high levels of EMF in their respective work environments. Although the increases in incidence were low as EMF exposures increased, they were sufficiently robust to lead the authors to conclude that their results, “taken together with previous epidemiological studies, suggest that exposure to EMF in the workplace may be associated with a slight elevation in breast cancer risk.”

Recently, a second very large population-based, case-control study from Poland found an increased risk for breast cancer in women working in white-collar jobs such as marketing, advertising, management, engineering (electrical, computer, industrial, etc.), social science and economics. Increased risk was also found in blue collar jobs including machine operators in a variety of settings. No single chemical or other exposure can be linked to the occupations with excess risk, leading the authors to conclude that possible associations of these occupations with EMF deserve further attention.

Norwegian researchers have reported an increased risk of breast cancer among female radio and telegraph operators exposed to radiofrequency (one type of EMF) and extremely low frequency EMF. Pre-menopausal women showed an increased risk of estrogen-receptor-positive tumors and post-menopausal women had an increased risk of estrogen-receptor-negative tumors.

Research on EMF exposure has shown increased mortality from breast cancer in women employed in the telephone industry. Further, premenopausal women appear to be at higher risk than post-menopausal women.

In 2004, a Norwegian study of residential and occupational EMF exposure found a 60 percent increase in breast cancer risk among Norwegian women of all ages living near high-voltage power lines. Occupational exposure also increased risk, but not as noticeably as residential exposure. Women younger than age 50 who were exposed to EMF both at home and at work had a modest increase in risk of breast cancer.

A 2003 study suggested that EMF exposure from electric bedding (electric blankets, mattress pads and heated waterbeds) may increase the risk of breast cancer in African American women. Researchers from Walter Reed Army Medical Center and Meharry Medical College compared 304 African American women with breast cancer to 305 African American women who did not have the disease. They found that the longer a woman used an electric bedding device, the greater her risk of breast cancer. Most earlier studies on electric bedding use among Caucasian women did not show an association with increased breast cancer risk.

Although breast cancer is rare in men, numerous studies point to a connection between EMF exposure and male breast cancer. A recent literature review on male breast cancer also identifies exposure to EMF as a risk factor.

EMF can also cause increases in mammary tumors in laboratory animals and in vitro systems in which human breast cell tumors are grown in culture. These live animal effects are found in some strains of animals but not others, indicating that subtle differences in genetic background might make some animals more susceptible to the carcinogenic effects of EMF.

The mechanisms by which EMF can affect health are not completely understood. The most widely studied model is built on the finding that EMF exposure and increased light-at-night (LAN) lower the body’s level of melatonin, a hormone secreted by the pineal gland during darkness. Through complex interactions with estrogens and cell signaling pathways, melatonin appears to have anti-cancer properties. In a variety of laboratory animal and in vitro systems, melatonin has inhibited the growth of mammary tumor cells.

Research has shown that exposure to light at night also decreases melatonin levels. This finding led to the hypothesis that night-shift work (working at night in a lighted environment) may increase the risk of breast cancer by lowering melatonin levels. Although this hypothesis remains controversial, at least three studies suggest a link between nightshift work and increased risk of breast cancer. A recent prospective study indicated that higher melatonin levels were associated with a lower risk of breast cancer.

The potential interaction of the hormonal effects of night-shift work together with other environmental exposures such as solar ionizing radiation and (until recently) secondhand smoke may help explain the elevated risk of breast cancer among flight attendants. Studies in Iceland, Sweden and California found varying degrees of increased incidence of breast cancer among flight attendants.

Learn more about policy and research recommendations to reduce exposure to radiation »

For references, see State of the Evidence 2008.