Thyroxine and Triiodothyronine in Commercially Available Thyroid Supplements?

A study recently published in the journal Thyroid found potentially dangerous adulteration in many popular thyroid supplements that should be of concern to all integrative practitioners.¹ The study looked at 10 commercially available thyroid health supplements sold via local retail stores or the Internet. Using the keywords “thyroid health,” “thyroid supplements,” and “thyroid support,” they found 5 herb-based and 5 desiccated thyroid tissue–based supplements to study. The 5 herb-based products also contained varying amounts of tyrosine and iodine and did not list or indicate that any animal tissue was used in the manufacturing of the products. The 5 products containing thyroid tissue were from bovine sources and described as including “raw thyroid” tissue, concentrate, or powder. 

 

The authors tested 3 samples from each product for thyroid hormones T3 and T4 using high-performance liquid chromatography. Each product was given a unique product identification number to blind laboratory investigators during product testing. Levothyroxine and liothyronine obtained from a local pharmacy served as controls and standards. 

 

The results? Nine out of 10 products tested positive for containing T3, with 4 out of 9 of those products exceeding a total daily dose of 10 µg per day. Five products contained detectable amounts of both T3 and T4. At the daily recommended dose of 4 capsules, one product contained thyroid hormone levels that reached doses restricted to availability by prescription only for both  T3 (at >5 µg/d) and T4 (at 25 µg/d). All of the herb-based supplements tested positive for T3, and 2 of these 5 products also tested positive for T4 at levels of 17 µg and 91 µg per day based on daily dose recommendations. The herb-based products contained iodine ranging from 100 mg to 225 mg and L-tyrosine ranging from 150 mg to 1000 mg. The authors noted that guggul (Commiphora mukul), kelp, ashwagandha (Withania somnifera), bladderwrack (Fucus vesiculosis), Coleus forskohlii, and Schisandra chinensis were the herbs commonly found in the botanical formulas.  

In the integrative community, it is commonplace to utilize dietary and botanical supplements to help support optimal health and vitality. Thyroid dysfunction is common, with nearly 5% of the US population above the age of 12 years having hypothyroidism.² The occurrence of hypothyroidism is even greater among older people, affecting 5%-20% of women and 3%-8% of men.³ The implications of this study are significant, as many patients seek integrative care for thyroid health, and according to this study’s results, a practitioner could unknowingly be medicating a patient with active thyroid hormone when recommending a thyroid support supplement.

This study suggests intentional adulteration of thyroid support supplements with T3 and T4 hormones in 9 out of 10 products sampled. It was alarming to note that the greatest levels of T3 were found not in thyroid glandular extracts but rather in the botanical supplements sampled. Every one of the botanical products sampled tested positive for T3, with the total daily dose ranging from 2.73 µg to 32.13 µg. Four of the products fall within range of or exceed prescription dosing treatment recommendations. The occurrence of only T3 in 4 of the products leads to speculation of selective adulteration of the hormone in these products. The authors also cited cases of adulteration in dietary supplements for weight loss; while not surprising, it is no less concerning. There are also well-documented instances of adulteration among popular botanicals, including ginkgo biloba, saw palmetto, and black cohosh, as well as other product categories such as sexual health and body-building supplements.^4-6

 

This study presents several issues of clinical importance. First is the potential danger of thyrotoxicosis secondary to adulterated thyroid support supplements. Second, this study demonstrates the need for clinicians to ask their patients for a complete list of dietary supplements and recognize the potential dangers that some of these products can pose. Third, clinicians need to discern whether or not the supplements recommended in clinical practice are exactly what they purport to be. Becoming familiar with and confident of the quality practices of preferred supplement manufacturers is of utmost importance. 

The study design would have been stronger if it had included a third category of products that contained only tyrosine and iodine. As thyroid hormones are built upon iodine and tyrosine, the authors should ensure that the methods used to evaluate hormone content adequately differentiate between iodine, tyrosine, and true T3/T4 content. This was not discussed in the study but could indicate a potential study flaw.

In 1994, the Dietary Supplement Health and Education Act (DSHEA) passed historical legislation that granted the US Food and Drug Administration the authority to prohibit unsafe and mislabeled dietary supplements. As of June 2010, all manufacturers are required to be compliant with DSHEA guidelines set for safety, consistency, quality, purity, and potency. However, there is clearly a need for manufacturers to exceed requirements set forth by DSHEA as the 800 plus–page document of guidelines does not guarantee all aspects of quality. Utilizing third-party certifications to verify current Good Manufacturing Practices compliance is one opportunity that manufacturers can employ to raise the bar on quality practices.  

 

There is also latitude in the DSHEA guidelines on frequency of batch testing of raw materials and finished products for purity and potency. Asking manufacturers how often they are testing their materials is another way to help discern quality practices. Does the manufacturer rely on the validity of the certificate of analysis provided by a supplier when purchasing raw materials, or does it utilize in-house or third-party testing laboratories to verify and guarantee quality? 

 

These are just a few of the questions one might consider when trying to determine their level of investment and commitment to quality practices. If you use thyroid support dietary supplements in your practice, ask the manufacturer if the product or its component ingredients have been tested for T3 and T4 adulteration. While there are many very high-quality dietary supplement manufacturers, this article serves as a reminder and opportunity to hold steadfast to quality practices in the dietary supplement industry as we strive to offer our patients the very best care.

 

This article was a part of the August 2014 special Natural Medicine Journal issue on endocrinology. To see the rest of the special issue, click here.