Magnetic Field Exposure and Cancer: Questions and Answers
Key Points
- Electric and magnetic fields (EMF) are areas of energy that surround any electrical device.
EMFs are produced by power lines, electrical wiring, and appliances (see Question
1).
- Electric fields are easily shielded or weakened by walls and other objects, whereas magnetic
fields are not. Since magnetic fields are more likely to penetrate the body, they are the component
of EMFs that are usually studied in relation to
cancer (see Question 1).
- Overall, there is limited evidence that magnetic fields cause childhood
leukemia, and there is inadequate evidence that these magnetic fields cause other cancers in
children (see Question 2).
- Studies of magnetic field exposure from power lines and electric blankets in adults show little
evidence of an association with leukemia,
brain tumors, or
breast cancer (see Question 3).
- Past studies of occupational magnetic field exposure in adults showed very small increases in
leukemia and brain tumors. However, more recent, well-conducted studies have shown inconsistent
associations with leukemia, brain tumors, and breast cancer (see Question 4).
|
-
What are electric and magnetic fields?
Electricity is the movement of electrons, or current, through a wire. The type of electricity that
runs through power lines and in houses is alternating current (AC). AC power produces two types of
fields (areas of energy)-an electric field and a magnetic field. An electric field is produced by
voltage, which is the pressure used to push the electrons through the wire, much like water being
pushed through a pipe. As the voltage increases, the electric field increases in strength. A magnetic
field results from the flow of current through wires or electrical devices and increases in strength as
the current increases. These two fields together are referred to as electric and magnetic fields, or
EMFs.
Both electric and magnetic fields are present around appliances and power lines. However, electric
fields are easily shielded or weakened by walls and other objects, whereas magnetic fields can pass
through buildings, humans, and most other materials. Since magnetic fields are most likely to penetrate
the body, they are the component of EMFs that are usually studied in relation to cancer.
The focus of this fact sheet is on extremely low-frequency magnetic fields. Examples of devices that
emit these fields include power lines and electrical appliances, such as electric shavers, hair dryers,
computers, televisions, electric blankets, and heated waterbeds. Most electrical appliances have to be
turned on to produce a magnetic field. The strength of a magnetic field decreases rapidly with
increased distance from the source.
-
Is there a link between magnetic field exposure at home and cancer in
children?
Numerous epidemiological (population) studies and comprehensive reviews have evaluated magnetic
field exposure and risk of cancer in children (1, 2). Since the two most common cancers in children are
leukemia and brain tumors, most of the research has focused on these two types. A study in 1979 pointed
to a possible association between living near electric power lines and childhood leukemia (3). Among
more recent studies, findings have been mixed. Some have found an association; others have not. These
studies are discussed in the following paragraphs. Currently, researchers conclude that there is
limited evidence that magnetic fields from power lines cause childhood leukemia, and that there is
inadequate evidence that these magnetic fields cause other cancers in children (2). Researchers have
not found a consistent relationship between magnetic fields from power lines or appliances and
childhood brain tumors.
In one large study by the National Cancer Institute (NCI) and the Children’s Oncology Group, researchers measured magnetic fields directly in
homes (4). This study found that children living in homes with high magnetic field levels did not have
an increased risk of childhood
acute lymphoblastic leukemia. The one exception may have been children living in homes that had
fields greater than 0.4 microtesla (µT), a very high level that occurs in few residences. Another
study conducted by NCI researchers reported that children living close to overhead power lines based on
distance measurements were not at greater risk of leukemia (5).
To estimate more accurately the risks of leukemia in children from magnetic fields resulting from
power lines, researchers pooled (combined) data from many studies. In one pooled study that combined
nine well-conducted studies from several countries, including a study from the NCI, a twofold excess
risk of childhood leukemia was associated with exposure to magnetic fields above 0.4 µT (6). In
another pooled study that combined 15 studies, a similar increased risk was seen above 0.3 µT (7).
It is difficult to determine if this level of risk represents a real increase or if it results from
study
bias. Such study bias can be related to the selection of study subjects or possibly to other
factors that relate to levels of magnetic field exposure. If magnetic fields caused childhood leukemia,
certain patterns would have been found such as increasing risk with increasing levels of magnetic field
exposure.
Another way that people can be exposed to magnetic fields is from household electrical appliances.
Several studies have investigated this relationship (2). Although magnetic fields near many electrical
appliances are higher than near power lines, appliances contribute less to a person’s total exposure to
magnetic fields. This is because most appliances are used only for short periods of time, and most are
not used close to the body, whereas power lines are always emitting magnetic fields.
In a detailed evaluation, investigators from NCI and the
Children’s Oncology Group examined whether the use of household electrical appliances by the mother
while pregnant and later by the child increased the risk of childhood leukemia. Although some
appliances were associated with childhood leukemia, researchers did not find any consistent pattern of
increasing risk with increasing years of use or how often the appliance was used (8). A few other
studies have reported mostly inconsistencies or no relation between appliances and risk of childhood
cancer.
Occupational exposure of mothers to high levels of magnetic fields during pregnancy has been
associated with childhood leukemia in a Canadian study (9). Similar studies need to be done in other
populations to see if this is indeed the case.
-
Is there a link between magnetic field exposure in the home and cancer
in adults?
Although several studies have looked into the relationship of leukemia, brain tumors, and breast
cancer in adults exposed to magnetic fields in the home, there are only a few large studies with
long-term, magnetic field measurements. No consistent association between magnetic fields and leukemia
or brain tumors has been established.
The majority of epidemiological studies have shown no relationship between breast cancer in women
and magnetic fields from electrical appliances. Recent studies of breast cancer and magnetic fields in
the home have included direct and indirect magnetic field measurements. These studies mostly found no
association between breast cancer in females and magnetic fields from power lines or electric blankets
(10, 11, 12, 13). A Norwegian study found a risk for exposure to magnetic fields in the home (14), and
a study in African-American women found that use of electric bedding devices may increase breast cancer
risk (15).
-
Is there a link between magnetic field exposure at work and cancer in
adults?
Several studies conducted in the 1980s and early 1990s reported that people who worked in some
electrical occupations (such as power station operators and phone line workers) had higher than
expected rates of some types of cancer, particularly leukemia, brain tumors, and male breast cancer
(2). Some occupational studies showed very small increases in risk for leukemia and brain cancer, but
these results were based on job titles and not actual measurements. More recently conducted studies
that have included both job titles and individual exposure measurements have no consistent finding of
an increasing risk of leukemia, brain tumors, or female breast cancer with increasing exposure to
magnetic fields at work (14, 16, 17, 18).
-
What have scientists learned from animal experiments about the relationship between magnetic
field exposure and cancer?
Animal studies have not found that magnetic field exposure is associated with increased risk of
cancer (2). The absence of animal data supporting carcinogenicity makes it biologically less likely
that magnetic field exposures in humans, at home or at work, are linked to increased cancer risk.
-
Where can people find additional information on EMFs?
The National Institute of Environmental Health Sciences (NIEHS) Web site has information about EMFs
and cancer, as well as information and publications related to the EMF Research and Public Information
Dissemination (RAPID) Program. NIEHS can be contacted at:
Note: Information about cancer risk and EMFs emitted from hand-held cellular phones (i.e., microwave
frequencies) can be found in the NCI fact sheet Cellular Telephone Use and Cancer, which is
available at http://www.cancer.gov/cancertopics/factsheet/Risk/cellphones
on the Internet.
Selected References
-
Ahlbom A, Cardis E, Green A, Linet M, Savitz D, Swerdlow A. Review of the epidemiologic literature
on EMF and health. Environmental Health Perspectives 2001; 109(6): 911–933.
-
World Health Organization, International Agency for Research on Cancer. Volume 80: Non-ionizing
radiation, Part 1, Static and extremely low-frequency (ELF) electric and magnetic fields. IARC Working
Group on the Evaluation of Carcinogenic Risks to Humans. 2002: Lyon, France.
-
Wertheimer N, Leeper E. Electrical wiring configurations and childhood cancer. American Journal
of Epidemiology 1979; 109(3): 273–284.
-
Linet MS, Hatch EE, Kleinerman RA, et al. Residential exposure to magnetic fields and acute
lymphoblastic leukemia in children. The New England Journal of Medicine 1997; 337(1): 1–7.
-
Kleinerman RA, Kaune WT, Hatch EE, et al. Are children living near high voltage power lines at
increased risk of acute lymphocytic leukemia? American Journal of Epidemiology 2000; 15:
512–515.
-
Ahlbom A, Day N, Feychting M, et al. A pooled analysis of magnetic fields and childhood leukaemia.
British Journal of Cancer 2000; 83(5): 692–698.
-
Greenland S, Sheppard AR, Kaune WT, Poole C, Kelsh MA. A pooled analysis of magnetic fields, wire
codes, and childhood leukemia. Childhood Leukemia-EMF Study Group. Epidemiology 2000; 11(6):
624–634.
-
Hatch EE, Linet MS, Kleinerman RA, et al. Association between childhood acute lymphoblastic leukemia
and use of electrical appliances during pregnancy and childhood. Epidemiology 1998; 9(3):
234–245.
-
Infante-Rivard C, Deadman JE. Maternal occupational exposure to extremely low frequency magnetic
fields during pregnancy and childhood leukemia. Epidemiology 2003; 14: 437–441.
-
Schoenfeld ER, O’Leary ES, Henderson K, et al. Electromagnetic fields and breast cancer on Long
Island: A case-control study. American Journal of Epidemiology 2003; 158: 47–58.
-
London SJ, Pagoda JM, Hwang KL et al. Residential magnetic field exposure and breast cancer risk: A
nested case-control study from a multi-ethnic cohort in Los Angeles, California. American Journal
of Epidemiology 2003; 158: 969–980.
-
Davis S, Mirick DK, Stevens RG. Residential magnetic fields and the risk of breast cancer.
American Journal of Epidemiology 2002; 155: 446–454.
-
Kabat GC, O’Leary ES, Schoenfeld ER, et al. Electric blanket use and breast cancer on Long Island.
Epidemiology 2003; 14(5): 514–520.
-
Kliukiene J, Tynes T, Andersen A. Residential and occupational exposures to 50-Hz magnetic fields
and breast cancer in women: A population-based study. American Journal of Epidemiology 2004;
159(9): 852–861.
-
Zhu K, Hunter S, Payne-Wilks K, et al. Use of electric bedding devices and risk of breast cancer in
African-American women. American Journal of Epidemiology 2003; 158: 798–806.
-
Tynes T, Haldorsen T. Residential and occupational exposure to 50 Hz magnetic fields and
hematological cancers in Norway. Cancer Causes & Control 2003; 14: 715–720.
-
Labreche F, Goldberg MS, Valois M-F, et al. Occupational exposures to extremely low frequency
magnetic fields and postmenopausal breast cancer. American Journal of Industrial Medicine
2003; 44: 643–652.
-
Willett E, McKinney PA, Fear NT, et al. Occupational exposure to electromagnetic fields and acute
leukaemia: Analysis of a case-control study. Occupational and Environmental Medicine 2003; 60:
577–583.
# # #
Related Resources
Publications (available at http://www.cancer.gov/publications)
National Cancer Institute (NCI) Resources
- Cancer Information Service (toll-free)
- Telephone: 1–800–4–CANCER (1–800–422–6237)
- TTY: 1–800–332–8615
- Online
- NCI’s Web site: http://cancer.gov
LiveHelp, NCI’s live online assistance:
https://cissecure.nci.nih.gov/livehelp/welcome.asp
Back to Top |