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Magnetic fields have been linked to childhood
cancer in many countries and now it's also been shown in Japan.
Michinori Kabuto, of the National Institute of
Environmental Studies in Ibaraki, along with a number of collaborators have found that children exposed to 4mG
(0.4µT) or more in their bedrooms had close to five times more leukemia than those living in low-exposure
homes. This statistically significant finding appears in the August 1st, 2006 issue of the International
Journal of Cancer (Volume 119, Issue 3, Pages 643-650).
One big advantage of this study is that it's the
first to measure residential magnetic fields over the course of a full week, rather than just 24 hours — as
was the case, for instance, in the 1997 U.S. National Cancer Institute study. These extra measurements
show that there was a great deal of variation in homes with high-field levels.
Kabuto explains that when he compared the leukemia
risk for each of the seven days separately, the leukemia risk on the highest exposure day was nearly twice that
for the lowest exposure day. That's a big difference and could explain some of the inconsistencies in past
studies.
On the negative side, the participation rate for
the controls was less than 30%, which is extremely low. Kabuto was well aware that this could have played
havoc wih his entire study and he did what he could to investigate its implications. "Selection bias per
se cannot fully explain our positive finding," he concludes.
Whatever its strength and weaknesses, the Japanese
study is the last major epidemiological study of EMFs and childhood leukemia we can expect for a long
time. Decisions concerning the adoption of precautionary policies will have to be made with the
information we now have in hand. |
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Abstract:
Residential power-frequency magnetic fields (MFs) were labeled as a
possible human carcinogen by the International Agency for Research on Cancer panel. In response to great
public concern, the World Health Organization urged that further epidemiologic studies be conducted in
high-exposure areas such as Japan.
We conducted a population-based case-control study, which covered
areas inhabited by 54% of Japanese children.
We analyzed 312 case children (0-15 years old) newly diagnosed with
acute lymphoblastic leukemia (ALL) or acute myelocytic leukemia (AML) in 1999-2001 (2.3 years) and 603
controls matched for gender, age and residential area.
Weekly mean MF level was determined for the child's bedroom. MF
measurements in each set of a case and controls were carried out as closely in time as possible to control for
seasonal variation. We evaluated the association using conditional logistic regression models. The
odds ratios for children whose bedrooms had MF levels of 0.4  T
or higher compared with the reference category (MF levels below 0.1 T)
was 2.6 (95% CI = 0.76-8.6) for AML + ALL and 4.7 (1.15-19.0) for ALL only.
Controlling for some possible confounding factors did not alter the
results appreciably. Even an analysis in which selection bias was maximized did not fully explain the
association.
Most of the leukemia cases in the highest exposure category had MF
levels far above 0.4 T.
Our results provided additional evidence that high MF exposure was associated with a higher risk of childhood
leukemia, particularly of ALL. |
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Research Contributors:
Michinori Kabuto, National Institute for Environmental Studies,
Ibaraki, Japan
Hiroshi Nitta, National Institute for Environmental Studies, Ibaraki,
Japan
Seiichiro Yamamoto, National Cancer Center, Tokyo, Japan
Naohito Yamaguchi, Tokyo Women's Medical University, Tokyo,
Japan
Suminori Akiba, Kagoshima University, Kagoshima, Japan
Yasushi Honda, University of Tsukuba, Ibaraki, Japan
Jun Hagihara, Miyagi University, Miyagi, Japan
Katsuo Isaka, Tokushima University, Tokushima, Japan
Tomohiro Saito, National Research Institute for Child Health
and Development, Tokyo, Japan
Toshiyuki Ojima, Jichi Medical School, Tochigi, Japan
Yosikazu Nakamura, Jichi Medical School, Tochigi, Japan
Tetsuya Mizoue, University of Occupational and Environmental
Health, Fukuoka, Japan
Satoko Ito, Hiroshima University, Hiroshima, Japan
Akira Eboshida, Hiroshima University, Hiroshima, Japan
Shin Yamazaki, Kyoto University, Kyoto, Japan
Shigeru Sokejima, Kyoto University, Kyoto, Japan
Yoshika Kurokawa, National Institute for Environmental Studies,
Ibaraki, Japan
Osami Kubo, Tokyo Women's Medical University, Tokyo, Japan |
