Iodine-induced hyperthyroidism

A 33-year-old woman began experiencing increased rate of hair loss, anxiety, insomnia, palpitations, heat intolerance and tremor in October. In December, she saw her primary care physician who found a fully suppressed thyroid-stimulating hormone level. Radioactive iodine uptake at six hours was 2.1% and at 24 hours was 2.8%. Anti-thyroid peroxidase antibodies were greater than 900.

When I saw her, I expected to discuss thyroiditis, how we manage and what to expect. However, I learned that several months prior to developing hyperthyroidism, an alternative nutritional therapist recommended that she increase her iodine intake. She was advised to add kelp to every meal and begin the nutritional supplement Iodoral (Optimox).

Iodine deficiency is an important public health issue in many places. As I have posted before, iodine deficiency results in endemic goiter and is the largest preventable cause of congenital mental retardation in the world. In iodine-sufficient countries, such as the United States, we much more frequently see the effects of iodine excess. Iodine excess is most commonly due to iodine-containing therapies, such as amiodarone or iodinated contrast. Occasionally, however, we see it due to excess dietary supplementation.

Iodine is required for the synthesis of thyroid hormone. In excess amounts, however, it can result in some interesting effects on the thyroid. Acute excess results in the Wolf-Chaikoff effect or transient suppression of thyroid hormone synthesis. Chronic excess can result in iodine-induced thyrotoxicosis, enhancement of thyroid autoimmunity, goiter formation and/or hypothyroidism. Normal adults are thought to be able to tolerate up to 1,000 mcg per day without ill effects. However, in those with pre-existing thyroid disease or iodine deficiency, the level where side effects can occur is much lower.

The current recommended daily intake of iodine is 150 mcg per day in nonpregnant adults. (Some have advised that this be increased slightly, but that is another discussion). The nutritional supplement that our patient was taking contains 12.5 mg (12,500 mcg) of iodine per tab, which is 83 times more than recommended daily intake. She also received an unknown additional amount of iodine from the kelp she was taking with her meals.

When I did an internet search, I found that some alternative health websites proclaim the benefits of taking high-dose iodine while downplaying or ignoring completely the potential for toxicity. One site stated that “ingesting up to 20 times the reference daily intake has no known side effects.” That is untrue as has been documented by decades of study. Some of these websites advise taking as many as four tabs per day of Iodoral, which would be 333 times the recommended daily intake!

With nutrients as with hormones, deficiency can cause harm but so too can excess. Our patient stopped all supplements and slowly she is feeling better. Her TSH remains low but the free thyroxine and free triiodothyronine have improved. The effects of iodine toxicity may persist for months. I am hopeful that with time the hyperthyroidism will resolve.

She has a very high titer of anti-TPO antibodies, however, and is at risk to develop hypothyroidism, if not now then in the future. She will need to be followed closely so that if that occurs, it will not be missed.