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Low Radiation Doses May Raise Cancer Risk

No Dose Is Too Tiny to Rule out a 'Small' Risk Increase, Say
Researchers

By Miranda Hitti
WebMD Medical News Reviewed By Brunilda Nazario, MD
on Thursday, June 30, 2005

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June 30, 2005 -- No dose of low-level radiation is too small to rule
out a "small" increase in cancer risk for humans, say researchers.

They reviewed data on the topic for the National Research Council. The
council is part of the National Academy of Sciences (NAS). The report
updates information from the 1990 findings, which is based mostly on
survivors of the 1945 atomic bomb attacks against Japan.

"The scientific research base shows that there is no threshold of
exposure below which levels of ionizing radiation can be demonstrated
to be harmless or beneficial," says Richard Monson, MD, ScD, in an NAS
news release.

Monson chaired the committee that wrote the report. He is also
associate dean for health education and an epidemiology professor at
Harvard School of Public Health.

'Very Small' Risk at Low Doses

"The health risks -- particularly the development of solid cancers in
organs -- rise proportionally with exposure," says Monson.

"At low doses of radiation, the risk of inducing solid cancers is very
small. As the overall lifetime exposure increases, so does the risk,"
says Monson.

The researchers define low-dose radiation as those ranging from close
to zero to about 100 millisieverts. The radiation dose from one chest
X-ray is about 0.1 millisieverts. A whole-body CT scan delivers about
10 millisieverts, say the researchers.

Researchers' Estimate

The report's predictions are based on information from survivors of the
atomic bombings in Hiroshima and Nagasaki, Japan. It estimates that
about one in 100 people in the U.S. would be expected to develop solid
cancer or leukemia from a dose of 100 millisieverts, say the
researchers.

For perspective, they say 42 in 100 people would be expected to develop
cancer from other causes.

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Low Radiation Doses May Raise Cancer Risk

No Dose Is Too Tiny to Rule out a 'Small' Risk Increase, Say
Researchers
(continued)
1 | 2



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Some Sources Are Natural

Low-level radiation is used in the medical field for X-rays and in
nuclear medicine to produce some of the scanned images of the body,
such as bone, lung, and thyroid scans. It is also found in the ground
and the universe.

About 82% of human exposure to radiation comes from natural sources --
soil, water, and some meats. Basic activities -- such as eating,
drinking, and breathing -- are most people's primary sources, say the
researchers.

People get exposed to about 3 millisieverts of natural "background"
radiation a year, they say.

The other 18% comes from man-made sources, they note. A smaller
percentage comes from consumer products such as tobacco, tap water,
building materials, occupational exposure, fallout, and the use of
nuclear fuel, say the researchers.

More Work Needed

More studies are needed to explore low doses of radiation and other
health problems, including heart disease, say the researchers.

"Radiation exposure has been demonstrated to increase the risk of
diseases other than cancer, particularly [heart] disease, in persons
exposed to high therapeutic doses and also in atomic-bomb survivors
exposed to more modest doses," they say.

"However, there is no direct evidence of increased risk of noncancer
diseases at low doses, and data are inadequate to quantify this risk if
it exists," they write.

Protection From X-ray and Gamma Radiation

Exposure to X-rays is almost entirely from dental and medical X-rays,
including mammograms. Simple MRI scanning does not expose a person to
X-rays; it uses radio waves and a strong magnetic field to produce body
images.

One way to protect yourself from excessive radiation from X-rays is to
make sure the technician performing the procedure has the proper
qualifications, says the Environmental Protection Agency. Simply ask
questions.

You might inquire about the necessity of having an X-ray or receive
assurance the X-ray machine has been inspected recently and that it is
properly calibrated.

You should be aware of steps taken to prevent exposures to other parts
of your body -- for example, through the use of a lead apron.


--------------------------------------------------------------------------------

SOURCES: The National Academies Report in Brief, "BEIR VII: Health
Risks from Exposure to Low Levels of Ionizing Radiation," June 2005.
News release, National Academy of Sciences. Environmental Protection
Agency.

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