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HTDS Guide > Findings and
Interpretations > Findings
HTDS Guide
| Findings and Interpretations |
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Findings
The HTDS data show that the risks of thyroid disease were about the
same regardless of the radiation doses people received. In other words,
no associations between Hanford's iodine-131 and thyroid disease were
observed.
The findings do not prove that Hanford radiation had no effect on the
health of the area population. However, the findings show that if there
is an increased risk of thyroid disease from exposure to Hanford's
iodine-131, it is probably too small to observe using the best
epidemiologic methods available.
Researchers studied all types of thyroid disease, as well as a
disease of the parathyroid glands called hyperparathyroidism, and
abnormalities of the thyroid gland that can be seen only on ultrasound
examinations.
In each case, the results were the same. The percentages of people
with each kind of thyroid disease or with ultrasound abnormalities were
about the same regardless of their estimated radiation dose from
Hanford's iodine-131. There were no statistically significant
dose-responses for any of the diseases or ultrasound abnormalities
studied.
Thyroid disease was found in the study population. This was expected
because thyroid disease is common in other populations, especially among
older people and women.
Researchers found that the rates of thyroid disease in the HTDS
population were generally consistent with the rates of disease detected
in other populations.
Thyroid Disease
Researchers studied all kinds of thyroid disease, including thyroid
cancer (see Figure 1), benign thyroid nodules (see
Figure 2) and hypothyroidism or underactive thyroid (see
Figure 3).
For each type of thyroid disease, the study found that people with
higher doses had about the same amount of disease as people with lower
doses.
Hyperparathyroidism
The study found no evidence that the risk of hyperparathyroidism
increased with increasing radiation dose. This disease occurs when the
parathyroid glands produce too much parathyroid hormone, resulting in
high calcium levels in the body.
However, the study did detect a statistically significant
relationship between radiation dose and decreasing calcium
levels. Average levels of calcium in the blood were slightly lower –
though still within the normal range – in people with higher estimated
thyroid radiation doses.
Researchers have no explanation for the finding. Nevertheless, the
decrease in calcium levels was so small that even participants with the
highest doses had calcium values within the normal range.
Non-Disease Outcomes
The proportion of participants with thyroid abnormalities that could
be seen on their ultrasound examinations did not increase significantly
with increasing radiation dose (see Figure 4).
Mortality in the Study Population
Of the 5,199 people originally identified for inclusion in the study,
researchers found that 527 were deceased. Researchers were able to
locate death certificates for 504 of the 527 deceased individuals. None
of the death certificates indicated that any thyroid disease, including
thyroid cancer, was responsible for any of the deaths.
Overall mortality rates in the study population were about the same
as those in the state of Washington for the same time period. However,
mortality rates for non-hereditary causes due to conditions that
occurred before or shortly after birth were somewhat higher than those
in the state of Washington for the same period. The reasons for this
higher death rate are not known, though it is not likely related to
Hanford's iodine-131 because increased death rates from these kinds of
conditions occurred even before the releases of iodine-131 from Hanford
began.
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