The Potential Dangers of Supplements and Herbal Products Marketed for Improved Thyroid Function

Victor Bernet; Ana-Maria Chindris

Disclosures

Expert Rev Endocrinol Metab. 2012;7(3):247-249. 

In This Article

Herbal Substances With an Effect on Thyroid Economy

Herbs are plants or plant products, including roots, stems, leaves, flowers, seeds or fruits, valued for their scent, flavor or medicinal properties. They can be marketed and sold in raw form or as extracts. Herbal medicine has been practiced for thousands of years with scarce scientific evidence regarding the safety and efficacy of most herbal products. Basic research over the past few decades demonstrates that several plants have an effect on thyroid economy or thyroid hormone metabolism, although the limited numbers of studies on human subjects have led to contradictory results. Guggulu (the gum resin of Commiphora mukul) is reported to raise the triiodothyronine (T3)/thyroxine (T4) ratio in female mice[1,2] and reverse the effects of propylthiouracil in hypothyroid mice by stimulating thyroid function.[1]

Radovic et al. demonstrated that xanthohumol (Humulus lupulus) stimulates iodide uptake while in a culture of normal non-transformed rat thyrocytes, possibly by influencing the activity of the sodium iodide symporter, a key protein in thyroid hormone production.[3] This effect actually makes xanthohumol a potential candidate for improving radioactive ablation of the thyroid gland by means of stimulating better radioiodine concentration. Similar effects were observed with forskolin (Coleus forskohlii) in RET/PTC1-expressing thyroid follicular cells.[4]

Withania somnifera is credited with anti-aging properties, sedative and anti-inflammatory effects, as well as increased serum T4 but not (T3) levels. It is thought to be a thyroid stimulant, while Bauhinia purpurea bark extract increased both T4 and T3 levels in female mice.[5] A similar effect was observed with Bacopa monnieri (Indian pennywort) extract, which increased both T4 and T3 levels in male mice.[6]

Moringa oleifera leaf extract has been observed to decrease the conversion of T4 to T3 in female but not in male adult Swiss rats, therefore increasing the T4/T3 ratio,[7] indicating a potential use for therapy of hyperthyroidism. Similar effects were observed with Aegle marmelos extract, which was observed to decrease T3 with an increase in T4 serum concentration in male mice.[6]

Even widely used Aloe vera extract has been reported to cause a mild decrease in both T4 and T3 concentrations in male mice.[6] Sea kelp (Ascophyllum nodosum) and bladderwrack (Fucus vesiculosus) are known dietary sources of natural iodine, which, in excess, can be associated with thyroid overactivity.

In addition to herbal products, ground thyroid extract of animal origin was widely used for the treatment of hypothyroidism before the era of synthetic thyroid hormones, and can be found today in some over-the-counter (OTC) preparations found in health food stores, on the internet or by mail order. Animal thyroid gland extract contains a combination of T4 and T3 that can widely vary in amount from batch to batchm and at times with a T3 content that is greater than what the human thyroid directly secretes on a daily basis.[8]

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