iThei mdcdaelcinfd o c elllllrllll do thlsdtcfdbhfenExcess Iodine Problematic
Excess iodine causes the thyroid to temporarily decrease function to pro-
tect against hyperthyroidism (Wolff-Chaikoff effect), which is a protec-
tive mechanism. Hypothyroidism attributed to the Wolff-Chaikoff effect
does not have an autoimmunity component.
Various studies found both autoimmune thyroiditis and non-autoim-
mune hypothyroidism can result from iodine excess.
Researchers in Iran were able to document the rates of thyroid peroxi-
dase antibodies (TPOAb) and thyroglobulin antibodies (TgAb) before
and after a national salt iodization program started in 1994. In 1983–
84, positive TPOAb and positive TgAb were found in 3.2 percent and
4 percent of the 465 adults selected for random sampling in Tehran.
This sampling was repeated with 1,426 adults in Tehran in 1999–2000,
this time showing 12.5 percent positive for TPOAb and 16.8 per-
cent positive for TgAb. The addition of iodine quadrupled the rate of
Hashimoto’s within a six-year span!
Studies in Greece, China, Sri Lanka, and Italy reported similar increases
in Hashimoto’s after the addition of iodine to salt.
Figure 5: Rates of Thyroid Peroxidase Antibodies (TPOAb) and
Thyroglobulin Antibodies (TgAb) in Tehran, Iran, before and after
a national salt iodization program