Thyroid Function and Iodine Intake

The thyroid gland plays its pivotal role in meeting the body’s needs by producing thyroid hormones, T3 and 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 at which point it is converted to its free elemental form, iodide which 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 stored in the thyroid gland ready for release into the blood stream.

As the very summarized 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 regions 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, daily intake maybe as high as 1000 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.

Food Serving Iodine (mcg)
Salt (iodized) 1 gram 77
Cod 3 ounces* 99
Shrimp 3 ounces 35
Fish sticks 2 fish sticks 35
Tuna, canned in oil 3 ounces (1/2 can) 17
Milk (cow’s) 1 cup (8 fluid ounces) 56
Egg, boiled 1 large 12
Navy beans, cooked 1/2 cup 32
Potato with peel, baked 1 medium 60
Turkey breast, baked 3 ounces 34
Seaweed 1/4 ounce, dried Variable*

* May be greater than 4,500 mcg (4.5 mg)

The risks of excess iodine intake on thyroid function:

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

  1. Iodine induced hypothyroidism which can occur via the following mechanisms:
    • Dampening organification; the process of iodination of tyrosines on thyroglobulin which is key in thyroid hormone synthesis.
    • Decrease 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; Iodine excess can act as an immune activator.

Sources of Excess Iodine:

  1. Over-the-counter and prescription medications that may be ingested or applied to the skin or vaginal mucosa.
  2. Radiographic contrast agents.
  3. Dietary supplements.
  4. Excessive intake of food sources.

Recommended Iodine Intake:

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

Age Group RDA
Infants up to 12 Months 110-130
Children up to 8 Years Old 90
Children up to 13 Years Old 130
Adults 150
Pregnant Women 220
Lactating Mothers 290

The Tolerable Upper Intake Level (UL) for adults, assessed by analyzing the effect of supplementation on thyroid-stimulating hormone, is 1100 micrograms/day (1.1 mg/day) for individuals with no known thyroid problem

To discover your path to wellness and schedule a health assessment, contact us today.