This MS describes the importance of selenium in thyroid disease monitoring. I can't access the full paper as it's behind a paywall.
Selenium in thyroid disorders — essential knowledge for clinicians
January 2020Nature Reviews Endocrinology 16(3)
DOI: 10.1038/s41574-019-0311-6
Kristian Hillert Winther, Margaret Philomena Rayman. Steen Joop Bonnema. Laszlo Hegedüs
Thank you, diogenes.
The abstract is available, thankfully:
Review Article
Published: 30 January 2020
Selenium in thyroid disorders — essential knowledge for clinicians
Kristian Hillert Winther, Margaret Philomena Rayman, Steen Joop Bonnema & Laszlo Hegedüs
Nature Reviews Endocrinology volume 16, pages165–176(2020)
Abstract
In the 1990s, selenium was identified as a component of an enzyme that activates thyroid hormone; since this discovery, the relevance of selenium to thyroid health has been widely studied. Selenium, known primarily for the antioxidant properties of selenoenzymes, is obtained mainly from meat, seafood and grains. Intake levels vary across the world owing largely to differences in soil content and factors affecting its bioavailability to plants. Adverse health effects have been observed at both extremes of intake, with a narrow optimum range. Epidemiological studies have linked an increased risk of autoimmune thyroiditis, Graves disease and goitre to low selenium status. Trials of selenium supplementation in patients with chronic autoimmune thyroiditis have generally resulted in reduced thyroid autoantibody titre without apparent improvements in the clinical course of the disease. In Graves disease, selenium supplementation might lead to faster remission of hyperthyroidism and improved quality of life and eye involvement in patients with mild thyroid eye disease. Despite recommendations only extending to patients with Graves ophthalmopathy, selenium supplementation is widely used by clinicians for other thyroid phenotypes. Ongoing and future trials might help identify individuals who can benefit from selenium supplementation, based, for instance, on individual selenium status or genetic profile.
doi.org/10.1038/s41574-019-...
I definitely noticed an improvement in my TED symptoms when taking 200mcg selenium daily. I’ve now reduced to 100mcg but will increase if my eye condition flares again. My antibodies have also reduced, but I understand this may be due to many factors (increased Levo, optimum vitamins etc).
I noticed there are several trials investigating selenium:
The chronic autoimmune thyroiditis quality of life selenium trial (CATALYST): study protocol for a randomized controlled trial.
ncbi.nlm.nih.gov/pubmed/247...
Selenium supplementation for patients with Graves’ hyperthyroidism (the GRASS trial): study protocol for a randomized controlled trial
ncbi.nlm.nih.gov/pmc/articl...
And the seemingly bizarre:
Investigating the Sensory Attributes of Selenium-fortified Biscuits and Their Effects on Selenium-status
clinicaltrials.gov/ct2/show...
Not read the article yet but concerned about the “narrow optimum range” as it is often recommended to supplement on this forum.
Apparently with hashimoto you can have get a blood results of over range selenium and will be still deficient or normal. It's something to do with thyroid gland not absorbing selenium and it going back to the bloodstream, but I don't know if that's exactly it. My levels were quite high after supplementation and I consulted a professor who specialises in selenium deficiency, he asked if I had Hashis, and apparently elevated Selevels can be normal.. again, forgot what the logic behind it was, but ranges for Hashis are different and higher for selenium, normal ranges don't apply. diogenes
Oh my! I didn’t know that. I lowered my dose as I was considerably over range. I was v worried. I have hashis.
I used to take 200mg a day and then reduce to 100mg as I read on here, very recently, that the recommendation uses to be 200 but is now 100. Im sorry I can’t remember who posted it but worth a search
We are supposed to be taking 200mg selenium for 3-12 months maximum. Maintenance doses were always lower considered as safe, in research papers, 55-75mg, or they should really be dietary. However, here is the sentence I found in below paper: "Several points, however, need clarification. Plasma or serum selenium concentrations do not reflect intrathyroid concentrations, and
assay of selenium levels is therefore not recommended in routine practice". And that professor researcher told me ranges for Hashis are different since there is no selenium in our thyroids, but this is a little outside of my comfort zone knowledge wise 
Which emphasises the need for due consideration about dosing AND regular testing.
On the basis that most authorities have said our actual daily requirements are less than 100 micrograms a day (numbers vary, but 75 would be fairly typical), and that we are reasonably good at absorbing selenium, I'd not want to go too high.
But we always have the issue that if someone is deficient, they might need a higher dose to get that deficiency corrected in a sensible period, then a lower maintenance dose.
I cannot see any answer other than testing. And, in the absence of testing, caution should prevail.
Thanks for the link to the full paper humanbean .
I just started to read it and came across a reference to rare mutations in SECISBP2 that cause errors in selenoprotein formation leading to reduced deiodinase activity. The authors describe the mutations as very rare. I wonder. My 23andMe results appear to indicate that I have this one, and I know Tania SS does too.
Very interesting. I did try selinium years ago recommended by a thyroid specialist but he didnt check my level - it didnt help me but I suspect I had plenty in my daily diet.
And the medical profession still say is all you heed to treat hypothyroidism is levothyroxine -simple! Simple my foot!
Ok to say that. But I have severe reactions to all brands and strengths in levo. So nothing else available on the nhs. So left untreated
Sorry to hear that Sh69. Your doctor has a duty of care to find the right treatment for you. Have you thought sbout asking to be referred to a specialist. Thyroid uk have a list of thyroid friendly doctors if you contact them. GPs can only prescribe levo that is true but a thyroid specialist has a wider brief and can prescribe alternatives if he/she can show there is a need. They will advise your GP who then carry it out.
I’m house bound due to chronic pain condition before being diagnosed with UAT. So don’t have options to leave the house or change doctors.
They know I cannot take levo and don’t seem bothered about it.
I take selenium every other day as worried about over doing it. All brands seem to do just 200mcg. Any lower branded product which are decent?
Also absorbing selenium do any foods or other vitamins interact with absorption which might reduce its affects? Or would this still result in to much?
There are quite a few products. On the basis of selenium content ONLY, I found the following:
Solgar-Selenium 100 ug (Yeast-Free Selenium)
Now Foods, Selenium Yeast Free 100 mcg
Vita World Selenium 100Mcg 100 Capsules
WARNKE Health Products 50, Sodium Selenite LENIT with 50 mcg Selenium 100 Tablets
But on the basis that our dietary intake will be up and down over days, I wouldn't worry about taking a 200 microgram tablet every two days. And, if they are splittable, I'd consider that.
It seems to be long term build up that could eventually be a problem, not day by day variation.
I used to take the selenium and zinc every evening. I now alternate the 2 as was getting night sweats and did not know if I was getting to much of a good thing as all test from gp came back normal. I’m using the h&b selenium which I know is not great quality.
Anyway thank you for the info.
A Brazil nut or two a day was recommended to me as a good source of selenium.
I believe not all Brazil nuts contain selenium
Correct, it depends if the soil was rich in selenium or not, some Brazil nuts are useless. But selenium is also in other products too
I buy organic and just assume they’re good.
5 Brazil nuts a day provide the perfect amount of Selenium a day. They have the perfect amount of what the thyroid needs because the Brazil nuts are seen as food. if you are not allergic, you should try and see for yourself. How they make you feel is what it is about.
Selenium...yes or no?
Selenium
What are the best vitamins for Graves Disease is CoQ10 Selenium, and L-Carnitine good supplements? 
Selenium - which type and for how long?
