Health Risks of Ionizing Radiation: - Clark University

Utah (thought to have had greater fallout exposure).
In response to this study a group of National Cancer
Institute scientists conducted their own analysis
based on the Lyon study design and using data from
the National Center for Health Statistics (NCHS)
(Land et al. 1984). These authors eliminated the first
control group, the 1944-50 birth cohort, because
the NCHS only provides data since 1950. This left
them with two groups to compare, the exposed birth
cohort and a 1959-78 birth cohort. Since leukemia
rates declined from 1950 to 1978 in the United States
generally, Land et al. claimed that the evidence did
not support the leukemia association; without an
early birth cohort, however, this study was not very
informative.
Carl Johnson (1984) conducted an analysis
of cancer among Utah Mormons, a group with
extensive health records and low background cancer
rates. Separating six towns as high fallout areas,
Johnson found excess cancer, particularly leukemia
and breast, bone and thyroid cancer. He also assessed
cancer incidence among Mormons who remembered
experiencing acute radiation effects such as skin
burns, hair loss or nausea. These subjects appeared to
have excess leukemia, lymphoma, and stomach and
breast cancer relative to all Utah Mormons. Again
the same three scientists from the NCI answered
with a reanalysis using NCHS data (Machado et al.
1987). Their study differed from Johnson’s in that it
used mortality rather than incidence as the endpoint
of concern, used county-level data for the three
southwestern Utah counties of Washington, Iron
and Kane, and used a slightly different definition of
the high-exposure time period group 8 . They failed to
find the excess cancers that Johnson found, with the
notable exception of leukemia.
Another ambitious paper associated leukemia
with fallout nationwide (Archer 1987). This simple
correlation experiment used state-level leukemia
data and compared them with three indexes of
exposure: Strontium-90 in cow milk, Stronium-
90 in human bone, and Strontium-90 in diet. Five
states ranked in the top five of all three indexes, and
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five states ranked in the bottom five; these became
the most exposed and least exposed states, with
all others classified as intermediate 9 . Leukemia
mortality rates in all states were higher in the 1960s
than in the 1950s or 1970s, but this by itself would
be only slightly suggestive of a link with fallout.
An additional piece of evidence for a possible
association is that the high exposure group showed
a higher mortality rate than the intermediate group,
and both were higher than the low-exposure group.
Finally, only the radiogenic leukemias (myeloid and
acute) showed a temporal association with fallout.
A couple of critical characteristics make this paper
statistically weak, however, including the huge
groupings of cases (states) and the lack of control
for possible confounding factors. In addition, the
exposure groups are not consistent with the recent
NCI/CDC feasibility report bone marrow dose
estimates (NCI 2001).
The most rigorous study to address the leukemia
issue was presented in 1990 by Walter Stevens,
Joseph Lyon and others. They estimated doses for
1,177 leukemia deaths and 5,330 matched controls
from the deceased membership file of the Mormon
Church. Both cases and controls were born before
November 1958 and died in the period 1952-1981.
This group also estimated bone marrow dose
based on the Town and County Databases of the
Department of Energy’s Offsite Radiation Exposure
Review Project. This study found increasing risk
with dose for all ages and all types of leukemia, but
this overall excess was not significant. Focusing
specifically on leukemia deaths in children, a
significant RR of 5.82 (1.55-21.8) was found when
comparing high doses (6-30 mGy) to low doses
(0-3 mGy), and a significant trend with dose was
observed. Similar results were found when limiting
the response to acute lymphocytic leukemia, and a
significant trend was also observed when limiting
observations to deaths between 1952 and 1957 (this
study is discussed further in appendix A).
Thyroid disease. Two studies have looked
8 Johnson defined the high exposure group as people born in 1962 or earlier and diagnosed with cancer in 1958 or
later. Machado et al. defined the high exposure group as people born in 1957 or earlier and dying after 1954 (of
leukemia or bone cancer) or after 1963 (of other cancers).
9 The high-exposure states were Georgia, Louisiana, Mississippi, North Carolina and Minnesota. The low-exposure
states were California, Florida, Hawaii, New Mexico and Texas.