#1 Likely Reason – Presence of goitrogens that compete with iodine for body’s receptors

A decreased dietary intake of iodine coupled with an increased intake of competing substances (called goitrogens) has created an epidemic iodine deficiency in America, which can cause both overactive and underactive thyroid function.    Iodine intake in the U.S. has fallen > 50% over the last 30 years while the presence of iodine antagonists, such as chlorine, fluoride and bromide from environmental pollution, and the considerable increase of soy products in our diet has increased considerably.   Hollowell J.G. et al, Iodine Nutrition in the United States. Trends and Public Health Implications: Iodine Excretion Data from National Health and Nutrition Examination Surveys I and III (1971-1974 ; 1988-1994) J of Clin. Endocr. & Metab.,1998

Fluoride, chlorine and bromine all “beat out” iodine.    Atomic weight determines which overpowers the other – fluoride is the overall winner, and iodine the loser.

Thyroid disorder-countering iodine used to be added to bread, but now thyroid disorder-causing bromate is added instead

From 1960-1980, iodine-containing dough conditioners added 150 mcg of iodine to each slice! But over the past 20 years, food processors have substituted this conditioner with bromate, a goitrogenic substance that easily binds to the thyroid gland’s iodine receptors and so inhibits iodine activity and contributes to thyroid disorders (Too much bromine can also cause impaired thinking and memory, drowsiness, dizziness and irritability). The substitution of bromine for iodine has resulted in nearly universal deficiency of iodine in the U.S..

Goitrogens vs. Iodine

Iodide in table salt is not very bioavailable.  Iodate in bread is very bioavailable, whereas only 10% of iodide in iodized salt is absorbed: Pittman, et al, measured serum inorganic iodide levels in two groups of subjects:

• GROUP 1: after iodization of salt, with an estimated daily intake of 750 mcg iodide,

and

• GROUP 2: after iodization of bread, with a similar average intake of iodates. The expected mean blood level at equilibrium would be 17.2 mcg/L (750 mcg/43.5 L). The mean values observed by Pittman, et al, were 1.7 mcg/L for subjects after iodization of salt, and 18.7 mcg/L for subjects after iodization of bread.

There is 30,000 times more chloride than iodide in iodized salt (on a molar basis).   Chloride competes with iodide for absorption in the intestinal tract. The low bioavailability of iodide in iodized table salt (sodium chloride) has not generally been reported. Pittman JA, et al. “Changing normal values for thyroidal radioiodine uptake.” NEJM, 1969; 280:1431-1434. PubMed

Iodized table salt isn’t providing sufficient iodine.  To get enough iodine to provide a maintenance dose for whole-body sufficiency (i.e. ~3mg), you would need to consume over an ounce of salt every day.

• Iodized salt contains a mere 0.076 mg of iodine / gram of salt.
• Sea salt, soy sauce, and Bragg’s liquid amino acids are all salty condiments that contain NO iodine.  Contrary to instinctive opinion, sea salt has very little iodide compared to iodized table salt. The concentration of iodide/iodate in the oceans is a very dilute 0.05 PPM (compare this to bromide, which is 1400 times more concentrated).

Only ~50% of Americans use iodized salt.  Many people are persuaded to reduce salt intake, usually because of high blood pressure concerns.

Low iodine content in soil

Some areas of the US, known as the Goiter Belt, simply have a very low iodine content.   This includes mountainous regions, the Mississippi River Valley, the Ohio River Valley, and the Great Lakes regions (e.g. 40% of the people living in Michigan suffered from goiter in the 1930’s). Also, over-farming has depleted iodine content in soils previously-rich in iodine. All soil containing granite is poor in iodine. E.g. Vermont. Coastal regions have a richer iodine content than inland (Iodide ions in seawater are oxidized to elemental iodine, which is volatilized by UV into the atmosphere and returned to the soil by rain, completing the cycle)