Tuesday, December 13, 2005

Date: June 29, 2005

FOR IMMEDIATE RELEASE

Low Levels of Ionizing Radiation May Cause Harm

WASHINGTON -- A preponderance of scientific evidence shows that even low doses of ionizing radiation, such as gamma rays and X-rays, are likely to pose some risk of adverse health effects, says a new report from the National Academies' National Research Council.

The report's focus is low-dose, low-LET -- "linear energy transfer" -- ionizing radiation that is energetic enough to break biomolecular bonds. In living organisms, such radiation can cause DNA damage that eventually leads to cancers. However, more research is needed to determine whether low doses of radiation may also cause other health problems, such as heart disease and stroke, which are now seen with high doses of low-LET radiation.

The study committee defined low doses as those ranging from nearly zero to about 100 millisievert (mSv) -- units that measure radiation energy deposited in living tissue. The radiation dose from a chest X-ray is about 0.1 mSv. In the United States, people are exposed on average to about 3 mSv of natural "background" radiation annually. (Clip)

Specifically, the committee's thorough review of available biological and biophysical data supports a "linear, no-threshold" (LNT) risk model, which says that the smallest dose of low-level ionizing radiation has the potential to cause an increase in health risks to humans. In the past, some researchers have argued that the LNT model exaggerates adverse health effects, while others have said that it underestimates the harm. The preponderance of evidence supports the LNT model, this new report says.

"The scientific research base shows that there is no threshold of exposure below which low levels of ionizing radiation can be demonstrated to be harmless or beneficial," said committee chair Richard R. Monson, associate dean for professional education and professor of epidemiology, Harvard School of Public Health, Boston. "The health risks – particularly the development of solid cancers in organs – rise proportionally with exposure. At low doses of radiation, the risk of inducing solid cancers is very small. As the overall lifetime exposure increases, so does the risk." The report is the seventh in a series on the biological effects of ionizing radiation.(Clip)

The report was sponsored by the U.S. departments of Defense, Energy, and Homeland Security, the U.S. Nuclear Regulatory Commission, and the U.S. Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter. A committee roster follows.

Copies of Health Risks from Exposure to Low Levels of Ionizing Radiation (BEIR VII - Phase 2) will be available this summer from the National Academies Press; tel. 202-334-3313 or 1-800-624-6242 or on the Internet at
http://www.nap.edu. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).

[ This news release and report are available at http://national-academies.org ]

NATIONAL RESEARCH COUNCIL
Division on Earth and Life Studies
Board on Radiation Effects Research

(Posted for educational and research purposes only,
in accordance with Title 17 U.S.C. section 107).

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