iThei mdcdaelcinfd o c elllllrllll do thlsdtcfdbhfenIn cases of severe iodine deficiency, conditions such as hypothyroidism,
goiter, and brain damage develop. Conversely, several studies show ex-
cessive iodine intake can lead to Hashimoto’s hypothyroidism, and io-
dine overconsumption is now recognized as an environmental trigger for
Hashimoto’s.
Hashimoto’s was not recognized in the United States before the nation-
wide salt iodization program began in 1924. In many other countries,
studies have shown rates of autoimmune thyroiditis increased drastically
after salt iodization programs.
Changes have been observed in the incidence of thyroid disorders with
very slight variations in iodine intake. In most cases of mild to moderate
iodine deficiency, the thyroid compensates and limits its use of iodine
for thyroid hormone production, keeping thyroid hormone production
normal. To achieve this, however, the thyroid gland enlarges, producing
a goiter.
A pattern of TSH levels dropping with advanced age is observed due
to the chronic enlargement and increased thyroid hormone production.
Thus, elderly persons in mild to moderate iodine-deficient conditions are
more likely to develop hyperthyroidism.
In contrast, populations with high iodine intake have been observed to
experience increasing TSH and rates of hypothyroidism as they age. It is
hypothesized that this may be due to the thyroid gland compensating to
adapt to high iodine levels. Caucasian populations seem to be especially
susceptible.
As iodine levels increase, more cell death is seen in the thyroid. Hydrogen
peroxide, a reactive oxygen species, is produced in the conversion of io-
dine to its usable state in the thyroid. The overabundance of hydrogen
peroxide causes damage to thyroid cells. White blood cells (lymphocytes)
come to “clean up” these dead thyroid cells.
Since thyroid peroxidase (TPO) is the enzyme involved in triggering
hydrogen peroxide release, perhaps the TPO enzyme becomes recog-
nized as an “invader” as it keeps causing damage to the surrounding
tissues through the release of hydrogen peroxide. The more iodine con-
sumed, the more there is to be converted, thus signaling more hydrogen
peroxide, which causes more lymphocytes to accumulate in the thyroid.
Perhaps there is a threshold of thyroid tissue damage as a result of hydro-
gen peroxide released that causes the body to recognize this physiological
process as a foreign invader.