June 30, 2005

Study shows radiation causes cancer but rarely

WASHINGTON (Reuters) - Exposure to everyday sources of
radiation, mostly medical X-rays, raises the risk of cancer but
not by much and there is no clear line between a harmless dose
and a disease-causing dose, an expert panel reported on

People should think twice about having unnecessary
high-dose X-rays such as the full-body CAT scans being offered
by some clinics, the panel advised, but otherwise should be
reassured by the findings.

The report from the National Research Council updates 1990
findings based mostly on survivors of the 1945 atomic bomb
attacks against Japan, about 45 percent of whom are still

A low dose of about 100 millisieverts of radiation -- the
equivalent of 1,000 chest X-rays -- can be expected to cause
cancer in one out of every 100 people, the report finds.

"About 42 additional people in the same group would be
expected to develop solid cancer or leukemia from other causes.
Roughly half of these cancers would result in death," adds the
report, available at http://national-academies.org.

Cancer is the second-biggest killer in much of the world
after heart disease.

The American Cancer Society estimates that nearly 1.4
million Americans will learn this year that they have cancer
and 563,700 will die of it, but it says two thirds of cases are
caused by tobacco use, poor eating, lack of exercise and

The report ties in with another issued on Wednesday, from
the International Agency for Research on Cancer in France,
which studied more than 400,000 nuclear industry workers and
found they had a 10 percent increased risk of death from

The National Research Council is part of the National
Academy of Sciences, an independent organization set up by
Congress to guide government on matters of health and science.

This is its seventh report on radiation.


"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 Monson, a professor of
epidemiology at the Harvard School of Public Health in Boston.

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

But the report said few people are exposed to very much
radiation. It recommends further study of infants and children
exposed to radiation through X-rays or radiation treatment for

It also recommends more study of people who get frequent
doses, such as those who get repeated CAT scans.

"I think what we can do is assure people that medical
radiation as currently done for good reasons is part of medical
care," Monson told a news conference.

"But ... prudence should be the guideline and exposure to
any unnecessary radiation should be avoided and what is
unnecessary is up to an individual."

Most sources of radiation are natural -- gamma rays from
space, and radon from the ground, air and water. "These sources
account for about 82 percent of human exposure," the report

The 18 percent of human-made radiation comes mostly from
medical radiation but also tobacco, televisions and smoke