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- Thyroid Hormones
- Dietary Supplement Safety
- Hyperthyroid
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Date:
07-31-2014 | HC# 021465-501
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Re: Study Reveals Possible Adulteration of Thyroid Dietary Supplements; however, Study Contains Flaws that Undermine Its Results
Kang
GY, Parks JR, Fileta B, et al. Thyroxine and triiodothyronine content in
commercially available thyroid health supplements. Thyroid. October
2013;23(10):1233-1237.
Incidences of
hyperthyroidism or thyrotoxicosis (toxic level of thyroid hormones) have been
found in people consuming dietary supplements marketed to address thyroid
problems, increase energy, or promote weight loss. The concentrations of thyroid
hormones contained in supplements is a legitimate safety concern, as consumers
and their physicians cannot determine the thyroid hormone content based on label
information. Thyroid hormone medication is classified as a narrow
therapeutic range drug by the Food and Drug Administration (i.e., there is a
very narrow margin between therapeutic and toxic doses), and therefore close
monitoring of thyroid hormone blood levels is required. This screening study
assessed the concentration of the thyroid hormones thyroxine (T4)
and triiodothyronine (T3) present in ten dietary supplements.
An Internet search using
the terms "thyroid health," "thyroid supplements," and
"thyroid support" was conducted. The ten products identified as
having the most commonly visited websites (the authors did not describe how
this was determined) were selected for evaluation. Five of the products were
herbal-based supplements (H) that did not have animal thyroid content reported on
the label. The other five products were labeled as containing bovine thyroid
tissue, concentrate, or powder (B).
The T4 and
T3 content in the supplements was analyzed at the pharmacy of Walter
Reed Army Medical Center in Bethesda, Maryland. The synthetic thyroid
replacement hormones levothyroxine and
liothyronine were used as positive controls and analytical standards. Three samples of each
supplement were assayed, and the personnel conducting the testing were blinded
to the identity of the samples. High-performance liquid chromatography coupled
with a photodiode array detector (HPLC-PDA) set at 225 nm was used to quantify the
hormone content; internal standards were used as a control for accuracy and
precision, and five concentrations of standards were used to create external calibration
curves, but the method was not properly validated. The identification of the thyroid
hormones was entirely based on the absorption at 225 nm, a wavelength where
many natural products absorb UV light, and therefore could be mistaken for the
thyroid hormones. Since some of the analyte peaks were so small that they were
almost indistinguishable from the background noise, the results of this paper
have to be considered speculative.
Based
on these speculative results, of the ten supplements tested for thyroid hormone
content, nine had T3 concentrations ranging from 1.3 to 25.4
µg/tablet, and one had no detectable T3. Taken at the manufacturer's
recommended dose, four of the supplements (three H, one B) would provide ˃15 µg/day
of T3. (The lowest prescription dosage is five µg/day; the maintenance
dose for hypothyroidism is 25-75 µg/day.) T3 is not a plant
constituent; it should not have been present in the three "herbal"
products. But since the identity of the analyte was not determined, it is
doubtful that the compound was truly T3.
Five
of the supplements had no detectable T4 content; the other five had a
T4 concentration ranging from ˂0.5 to 22.9 µg/tablet (three H, two B).
If taken at the recommended dosage, the maximum daily consumption of T4
would be as much as ˃90 µg/day for one H supplement. (The lowest prescription dosage
is 25 µg/day; the average dose for hypothyroidism is 100-125 µg/day for a 70-kg
adult.) T4 is not a plant constituent; it should not have been
present in the three "herbal" products, which again raises the
question if the analyte was indeed T4.
Five
supplements (three H, two B) had detectable concentrations of both T3
and T4. Taken at the manufacturer's recommended dose, theoretically,
the H product with the greatest T3 and T4 content would
provide 16.53 and 91.6 µg/day, respectively.
Of
the five supplements labeled as containing bovine thyroid tissue, extract, or
concentrate, one had no detectable T3 or T4, two contained
T3 only, and two had detectable concentrations of both T3
and T4. Taken in order, these findings indicate that one product was
falsely labeled (did not contain bovine thyroid), two products were adulterated
with synthetic T3 (authentic animal material would contain both T3
and T4), and two products actually contained T3 and T4
(synthetic hormones or thyroid tissue/extract/concentrate).
In
the five supplements that were described as containing botanical ingredients
but no animal thyroid content, 150-1000 mg of L-tyrosine (recommended daily
allowance [RDA] 231 mg/day) and 100-240 µg of
iodine (RDA 150 µg/day) were detected. Taken
as recommended, these supplements would provide two to four times the RDA.
All five of the
"herbal" supplements that had no animal thyroid ingredients listed on
their label contained T3, and two also contained T4. The
authors state, "The presence of T3
alone in some of the samples would appear to implicate selective addition of
this hormone to the product, as those containing a desiccated animal source
would be expected to have both T4 and T3 present." Again, since
the detection method was non-specific for the thyroid hormones, the identity of
the peaks eluting at the same time as the T3 and T4
standards remains unknown. Most likely, these compounds were components of the
botanical extracts present in the products rather than T3 and T4.
The evidence from
this study focuses attention on two important public health issues. If present,
clinically significant amounts of T3 and T4 in these
readily available dietary supplements would constitute a potential medical
hazard that may cause hyperthyroidism in unwitting consumers. The authors call
for more widespread education on the potential risks of these supplements and
more rigorous regulation.
The
second fact is that the chemical analysis indicated that most of the products assessed
in this study were adulterated or had false label claims. Only two of the five products
purporting to contain "bovine thyroid" actually contained both T3
and T4, and all five of the purported "herbal" products
contained T3.
The
third fact is that all the results were based on inadequate science. It is
unfortunate that the authors used a method that carries a high risk of
providing erroneous results and therefore are making conclusions that will
misinform health care professionals and the dietary supplement industry. The
authors' attempts to raise awareness of a possibly serious problem in this case
have failed due to the use of an inappropriate analytical method.
This
study was limited in that the sample size was small and potentially biased, and
most importantly, the identity of the products analyzed (manufacturer, lot,
batch number) was not reported so it cannot be reproduced.
—Amy C. Keller,
PhD
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