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January 2014

Thyroid Hormones Identified in Dietary Supplements

Many commercially available dietary supplements marketed as natural thyroid boosters may contain clinically relevant amounts of thyroid hormones, according to a new study.

Thyroid hormones, triiodothyronine (T3) and thyroxine (T4), are hormones that are mainly responsible for the regulation of metabolism. Release of thyroid hormones is controlled by the hypothalamus and pituitary gland, both found deep inside the brain. One of the most important features of the endocrine system is its regulation (control) by negative feedback. This means that the glands that stimulate the release of a hormone (for example, the pituitary) from another gland (for example, the thyroid) are eventually shut off, in a sense, so that too much hormone is not produced. Hyperthyroidism occurs when the thyroid gland produces too much thyroxine and hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone.

In a recent study, researchers purchased 10 commercially available thyroid dietary supplements. The supplements were then dissolved and analyzed using high-performance liquid chromatography to identify the presence of both T4 and T3.

The researchers found that nine out of the 10 dietary supplements contained measurable amounts, 1.3-25.4 micrograms per tablet, of T3, and five out of 10 contained measurable amounts, 5.77-22.9 micrograms per tablet, of T4. The authors noted that when taken at the dose recommended on the bottle, five of the 10 supplements provided over 10 micrograms of T3 daily.

The authors concluded that many commercially available thyroid dietary supplements may contain clinically relevant amounts of thyroid hormones. Additionally, some products may even provide amounts greater than those used to treat hypothyroidism. The authors stressed the importance of patient education on the potential dangers associated with using these products.


  1. Kang GY, Parks JR, Fileta B, et al. Thyroxine and triiodothyronine content in commercially available thyroid health supplements. Thyroid. 2013 Oct;23(10):1233-7. doi: 10.1089/thy.2013.0101.
  2. Natural Standard: The Authority on Integrative Medicine. 

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