Thyroid function and iodine intake

The importance of iodine with respect to healthy thyroid function cannot be overstated.

by Dr. Sima Aidun — 

The thyroid gland plays a pivotal role in meeting the body’s needs by producing thyroid hormones — triiodothyronine (T3) and thyroxine (T4) — with iodine playing the key role in this process. The path from iodine to T3 and T4, a somewhat complicated chemical process, begins at the point of iodine’s introduction to the thyroid, where it is converted to its free elemental form, iodide. It then undergoes oxidation and is incorporated into intermediate hormones known as monoiodotyrosine (MIT) and diiodotyrosine (DIT), which in turn combine to produce the T3 and T4 hormones that are stored in the thyroid gland ready for release into the bloodstream.

As the summary description above demonstrates, the importance of iodine with respect to healthy thyroid function cannot be overstated.

Food sources of iodine

Iodine intake varies somewhat across different regional populations of the globe. In regions where the typical diet consists of large amounts of iodine-rich kelp and other seaweeds, such as Japan and Korea, individual daily intake may be as high as 1,000 micrograms or more. Although iodine consumption is generally lower in North America and Europe, the populations in these regions do not experience a high rate of thyroid disease due to salt fortification with iodine to ensure sufficient intake.

The risks of excess iodine intake on thyroid function

Iodized salt has more or less eliminated the problems associated with inadequate iodine intake. Indeed, when it comes to thyroid disease in the U.S., excessive iodine intake is the most contributing factor and can lead to:

1. Iodine-induced hypothyroidism which can occur via the following mechanisms: a) dampening organification; the process of iodination of tyrosines on thyroglobulin which is key in thyroid-hormone synthesis and b) decrease in the conversion of T4 (biologically inactive) to T3 (biologically active) thyroid hormone.
2. Iodine-induced hyperthyroidism: increase in synthesis of thyroid hormones.
3. Aggravation of thyroid autoimmune disorders, such as Hashimoto’s Thyroiditis, in which excess iodine can act as an immune activator.

Sources of excess iodine include over-the-counter and prescription medications that may be ingested or applied to the skin or vaginal mucosa, radiographic contrast agents, dietary supplements and excessive intake from food sources.

Recommended iodine intake

The body’s only natural source of iodine is diet. A balanced iodine intake is crucial to a proper functioning thyroid. The United States Institute of Medicine recommends the following daily iodine intake (in micrograms/day):

• Infants up to 12 months: 110-130 mcg
• Children up to 8 years old: 90 mcg
• Children up to 8 to 13 years old: 130 mcg
• Adults: 150 mcg
• Pregnant women: 220 mcg
• Lactating mothers: 290 mcg

The Tolerable Upper Intake Level (UL) for adults, assessed by analyzing the effect of supplementation on the thyroid-stimulating hormone, is 1,100 micrograms/day (1.1 mg/day) for individuals with no known thyroid problem.

Dr. Sima Aidun is a naturopathic medical doctor whose practice focus is on integrative endocrine care. 480-451-1602 or www.focusedmedicineaz.com.

Reprinted from AzNetNews, Volume 30, Number 4, August/September 2011.