The Importance of Specificity – Alleged Adulteration of Dietary Supplements with Thyroid Hormones Based on Inadequate Analytical Testing

Reviewed: Kang GY, Parks JR, Fileta B, et al. Thyroxine and triiodothyronine content in commercially available thyroid health supplements. Thyroid. 2013;23(10):1233-1237. http://cms.herbalgram.org/herbclip/501/021465-501.html.

Many health supplements containing herbal extracts or animal-based thyroid tissue are marketed to improve thyroid function. Popular ingredients found in the herbal-based supplements were guggul (Commiphora mukul, Burseraceae) gum, kelp (a variety of genera of brown algae; Laminaria spp., Laminariaceae), ashwagandha (Withania somnifera, Solanaceae) root, bladderwrack (Fucus vesiculosus, Fucaceae), forskohlii (Plectranthus barbatus syn. Coleus forskohlii, Lamiaceae) herb, and schisandra (Schisandra chinensis, Schisandraceae) fruit. One of the concerns with animal-based products in particular is the presence of unknown amounts of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). The thyroid hormones are involved in the development and differentiation of all cells in the human body, and regulate protein, fat, and carbohydrate metabolism. Dietary supplements containing clinically relevant amounts of T3 and/or T4 have been implicated in rare cases of thyrotoxicosis. The aim of this study was to determine the amounts of T3 and T4 in dietary supplements marketed for thyroid support and – if present – determine the daily dosage of thyroid hormones delivered when used according to the manufacturer’s dosage recommendations.

The authors analyzed ten commercial products (five herbal products and five products labeled to contain thyroid tissue) by HPLC-UV, detecting at 225 nm, based on methods published for pharmaceutical preparations. Standards of T3 and T4 were used to calibrate and to assess the accuracy and precision. The authors detected T3 in 90% and T4 in 50% of the supplements, which led them to believe that the hormones were selectively added to the products without disclosing them on the label. Based on the quantitative results, the daily intake was between 0 and 32 µg/day and 0 and 92 µg/day for T3 and T4, respectively, well within the therapeutic range of standard thyroid hormone dosing in patients with hypothyroid.

Comment: This well-meant attempt to raise awareness of potentially problematic dietary supplement ingredients has led to doubtful results due to the application of an inadequate analytical method. In particular, the use of a UV detector at 225 nm is not suitable to quantify T3 and T4 in dietary supplements, which can contain hundreds of compounds that absorb at this wavelength and could be mistakenly quantified as thyroid hormones. The specificity of the method has not been evaluated, and therefore, the results of the study have to be called into question. In addition, the size for the alleged T3 and T4 peaks was in some instances very similar to the background noise and likely below the limit of quantification. Therefore, the purported adulteration of herbal-based supplements (i.e., those not containing animal tissue-based ingredients) with thyroid hormones – insofar as this study is concerned – is probably unfounded.