We
need to be careful regarding Milk Thistle. There have been many claims
for Milk Thistle over the years. Often suggested for people with
liver-related issues.
But the only person I know who tried it felt unwell from taking it. So I have long been cautious.
This is a long and detailed page by Tania S. Smith, PhD, on the excellent Thyroid Patients Canada site which explains the issues and specific circumstances in which it should be avoided.
If you are considering taking Milk Thistle it really is worth some time reading this first.
Milk thistle alters thyroid hormone transport
January 16, 2022
https://thyroidpatients.ca/2022/01/16/milk-thistle-thyroid-transport/
This paper identifies a potentially significant issue with a constituent of Milk Thistle.
Endocrinology . 2016 Apr;157(4):1694-701.
doi: 10.1210/en.2015-1933. Epub 2016 Feb 24.
Silychristin, a Flavonolignan Derived From the Milk Thistle, Is a Potent Inhibitor of the Thyroid Hormone Transporter MCT8
Jörg
Johannes 1 , Roopa Jayarama-Naidu 1 , Franziska Meyer 1 , Eva Katrin
Wirth 1 , Ulrich Schweizer 1 , Lutz Schomburg 1 , Josef Köhrle 1 ,
Kostja Renko 1
Affiliations
• PMID: 26910310
• DOI: 10.1210/en.2015-1933
Abstract
Thyroid
hormones (THs) are charged and iodinated amino acid derivatives that
need to pass the cell membrane facilitated by thyroid hormone
transmembrane transporters (THTT) to exert their biological function.
The importance of functional THTT is affirmed by the devastating effects
of mutations in the human monocarboxylate transporter (MCT) 8, leading
to a severe form of psychomotor retardation. Modulation of THTT function
by pharmacological or environmental compounds might disturb TH action
on a tissue-specific level. Therefore, it is important to identify
compounds with relevant environmental exposure and THTT-modulating
activity. Based on a nonradioactive TH uptake assay, we performed a
screening of 13 chemicals, suspicious for TH receptor interaction, to
test their potential effects on THTT in MCT8-overexpressing MDCK1-cells.
We identified silymarin, an extract of the milk thistle, to be a potent
inhibitor of T3 uptake by MCT8. Because silymarin is a complex mixture
of flavonolignan substances, we further tested its individual components
and identified silychristin as the most effective one with an IC50 of
approximately 100 nM. The measured IC50 value is at least 1 order of
magnitude below those of other known THTT inhibitors. This finding was
confirmed by T3 uptake in primary murine astrocytes expressing
endogenous Mct8 but not in MCT10-overexpressing MDCK1-cells, indicating a
remarkable specificity of the inhibitor toward MCT8. Because silymarin
is a frequently used adjuvant therapeutic for hepatitis C infection and
chronic liver disease, our observations raise questions regarding its
safety with respect to unwanted effects on the TH axis.
Full paper accessible here:
https://academic.oup.com/endo/article/157/4/1694/2422745?login=false
There
has long been the received wisdom that T3 does not cross the placenta. I
am not aware this has been proved in any level of detail.
This paper appears to make that look wrong.
Indeed, it appears to identify specific pharmaceutical agents which directly and significantly affect T3 transport.
Silychristin
is a constituent of Milk Thistle extract and its impact suggests that
it should be avoided in pregnancy - and possibly other circumstances.
Thyroid Vol. 32, No. 9 Thyroid Economy: Regulation, Cell Biology, and Thyroid Hormone Metabolism and Action
Thyroid Hormone Transporters in a Human Placental Cell Model
Zhongli Chen,
A.S. Elise van der Sman,
Stefan Groeneweg,
Linda Johanna de Rooij,
W. Edward Visser,
Robin P. Peeters, and
Marcel E. Meima
Published Online:14 Sep 2022 https://doi.org/10.1089/thy.2021.0503
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Abstract
Background: Fetal brain development in the first half of pregnancy is dependent on maternal thyroid hormone (TH), highlighting the importance of trans-placental TH transport. It is yet unclear which transporters are involved in this process. We aimed to identify the major TH transporters in a human placental cell model (BeWo cells).
Methods:
Messenger RNA expression of the known TH transporters (the
monocarboxylate transporter [MCT]8, MCT10, the L-type amino acid
transporter [LAT]1, LAT2, the organic anion transporting peptide
[OATP]1A2 and OATP4A1) in BeWo cells and human placenta were determined
by quantitative PCR. To determine the specificity and efficacy of
transporter inhibitors, we first determined TH uptake at different
inhibitor concentrations in African green monkey kidney fibroblast-like
cells (COS1 cells) overexpressing TH transporters. We then tested TH
uptake in BeWo cells in the presence or absence of the optimal inhibitor
concentrations.
Results:
All tested TH transporters were expressed in human term placentas,
whereas MCT8 was absent in BeWo cells. Both
2-amino-2-norbornanecarboxylic acid (BCH) and L-tryptophan at 1 mM
inhibited LATs, whereas at the highest concentration (10 mM)
L-tryptophan also inhibited MCT10. Verapamil inhibited OATP1A2 and less
efficiently both MCTs, but not LATs. Both rifampicin and naringin
reduced OATP1A2 activity. Finally, silychristin inhibited MCT8 at
submicromolar concentrations and OATP1A2 partially only at the highest
concentration tested (10 μM). In BeWo cells, verapamil reduced
triiodothyronine (T3) uptake by 24%, BCH by 31%, and 1 mM L-tryptophan
by 41%. The combination of BCH and verapamil additively decreased T3
uptake by 53% and the combination of BCH and 10 mM L-tryptophan by 60%,
suggesting a major role for MCT10 and LATs in placental T3 uptake.
Indeed, transfection of BeWo cells with MCT10-specific small interfering
RNA significantly reduced T3 uptake. Only the combination of BCH and
verapamil significantly reduced thyroxine (T4) uptake in BeWo cells, by
32%.
Conclusions:
Using pharmacological inhibitors, we show that MCT10 and LATs play a
major role in T3 uptake in BeWo cells. T4 uptake appears independent of
known TH transporters, suggesting the presence of, currently unknown,
alternative transporter(s).
Full paper accessible here:
https://www.liebertpub.com/doi/10.1089/thy.2021.0503
And this is a search for other Thyroid UK (HealthUnlocked) posts about Milk Thistle.
https://healthunlocked.com/thyroiduk/search/posts?query=milk%20thistle&page=1
If you wish to link to this page on HealthUnlocked, copy the entire dark red text below and paste into a post or reply.
[i][b]helvella - Milk Thistle, Silymarin & Silychristin[/b]
Some information and cautions regarding the use of Milk Thistle and its derivatives, especially in those with thyroid issues.
Last updated 10/02/2025[/i]
Link to blog:
https://helvella.blogspot.com/p/helvella-milk-thistle-silymarin.html
If you find anything incorrect, misleading, typos, links
that don’t work, etc., please let me know. Go to my profile and use the contact details there.
