Thyroid follicles pump iodide in through NIS, and attaches the iodine to thyroglobulin to make and , which needs enough iodine, selenium and iron.The thyroid is built from a great many follicles — each a sealed sphere:
· Thyrocytes (follicular epithelial cells) form the wall. · The lumen (colloid) stores thyroglobulin (Tg) — a giant carrier protein.
The three-piece machine:
· NIS (sodium-iodide symporter) — on the basolateral side, pumps I⁻ from blood into the cell. · Pendrin — moves I⁻ across the apical membrane into the colloid. · (thyroid peroxidase) — on the colloid side, oxidizes I⁻ to reactive iodine and attaches it to tyrosine residues on Tg → forms MIT/DIT → couples them into (4 iodines) / (3 iodines).
Output:
· Under signalling, stored T4/T3 is endocytosed back into the cell, cut free from Tg, and released into blood. · Most of what is secreted is T4 (about 80%, relatively inert), with a little of the more active T3; peripheral deiodinases (DIO1/2) then convert T4 → T3.
This all requires enough I + Se + Fe:
· I — raw material ( 150 µg; pregnancy 220 µg). · Se — TPO itself does not use Se directly, but the GPx + Trx antioxidant system around the colloid needs Se to clear the H₂O₂ produced by the TPO reaction. · Fe — TPO is a heme enzyme; iron deficiency lowers its activity.
2 · Autoimmune attack
In Hashimoto thyroiditis the immune system mistakes its own and Tg for an enemy, T cells kill follicular cells, and the gradual destruction can end in hypothyroidism.Hashimoto's thyroiditis is the immune system mistaking its own + Tg for a foreign enemy:
Serum markers:
· Anti-TPO antibodies (TPOAb) — positive in about 90% of people with Hashimoto's, and highly specific for it. · Anti-Tg antibodies (TgAb) — positive in 60-80%, less specific. · Positive antibodies + raised + an ultrasound showing a low, uneven echo pattern → supports the diagnosis.
Pathology (lymphocytic infiltration):
· CD4⁺ T cells + CD8⁺ T cells + B cells infiltrate the thyroid and form lymphoid follicles. · T cells directly kill follicular cells + B cells secrete antibodies. · The antibodies themselves may not be the main destroyers — they look more like a marker that destruction is happening.
Outcome:
· Follicles are gradually destroyed → stored / may leak out briefly (a short hyperthyroid phase) → then runs out → hypothyroidism. · Many people eventually develop clinical hypothyroidism and need long-term levothyroxine. · Some stay in subclinical hypothyroidism (TSH ↑ + normal FT4) for a long time, which does not always need treatment.
Why does the immune system attack itself?
· Genetics: when a first-degree relative is antibody-positive, the risk is roughly 5-10 times higher; HLA-DR3 / -DR5 / CTLA-4 / PTPN22 and other genes are involved. · Suspected environmental triggers: high iodine, pregnancy (especially after delivery), viral infection. · Far more women than men: worldwide, 5-15% of women and 1-3% of men test positive for anti-TPO or anti-Tg antibodies (being antibody-positive is not the same as being hypothyroid).
3 · Selenium · antibodies fall, window is narrow
3 months of selenium clearly lowered anti- antibodies in Hashimoto patients, but lower antibodies do not mean a cure, and the selenium safety window is narrow.The real evidence on selenium in Hashimoto's: not that selenium cures Hashimoto's, but that selenium brings anti- antibodies down:
Mechanism (it makes sense, but how much it matters in Hashimoto's is not yet clear):
· The TPO reaction uses H₂O₂ as its oxidizer. · Normally the GPx + Trx system (selenium-dependent) around the colloid clears the H₂O₂. · By the mechanism: low selenium → low GPx activity → H₂O₂ builds up → more oxidative damage to the follicle → more inflammation.
Clinical evidence:
· Toulis 2010 (4 randomized, double-blind, placebo-controlled trials, all in people with Hashimoto's already on levothyroxine): · 3 months of selenium (200 µg/day in most trials) → anti-TPO antibodies clearly lower than in the control groups · More people reported better well-being or mood; levothyroxine dose and ultrasound appearance were unchanged or not reported · The authors' own conclusion: an improvement in thyroid function and structure must be shown before routine selenium can be recommended · Lower antibodies ≠ cured: antibodies are traces left by the immune attack, not a reading of thyroid output; whether you feel cold or sluggish depends on and free
The safety window is narrow:
· SELECT used 200 µg of selenium (the 400 is the vitamin E dose in ), and the diabetes risk it found was not significant ( 1.07, P = 0.16) · The significant signals came from the NPC trial, also at 200 µg/day: type 2 diabetes 1.55 (1.03-2.33), concentrated in the third of people whose baseline selenium was already adequate (Stranges 2007); squamous cell carcinoma HR 1.25 (1.03-1.51) (Duffield-Lillico 2003) · 400 µg/day is the tolerable upper intake level (), not a harm line measured in any trial — for people who are not short of selenium, even 200 µg may not be a net gain
Practical:
· If you do supplement, the usual amount is 100-200 µg a day, and it is best to check with a doctor first whether you are short; if you are pregnant and positive for anti-TPO antibodies, the American Thyroid Association does not recommend selenium supplements · 1-2 Brazil nuts (selenium per nut varies a lot) or fish, eggs and whole grains are usually enough; if you already eat Brazil nuts, do not stack selenium tablets on top · Not a cure: once Hashimoto's reaches hypothyroidism, levothyroxine remains the mainstay
Note: raw milk, a strict AIP diet and iodine supplements for Hashimoto's have no randomized trials showing they work, and high-dose iodine may even backfire.
4 · Iodine paradox
Iodized salt sharply cut goiter, but more iodine is not simply better: after Denmark cautiously added iodine, anti- positivity rose from 14.3% to 23.8%.Hashimoto's + iodine: one of the more counterintuitive links in nutrition. In public health, iodized salt has sharply cut endemic goiter and cretinism; but more iodine is not simply better.
Population evidence: Denmark ran the same national sample survey twice, before and after a cautious iodization program (two cross-sectional surveys, not a follow-up of the same people). Median urinary iodine only moved from mild deficiency to just enough, yet four or five years later anti- positivity had risen from 14.3% to 23.8%, most clearly in young women and in the low-titer band (Pedersen 2011). It measured more people becoming antibody-positive, not people already positive progressing faster — the study did not measure the second thing.
Mechanism (reasoning, not yet shown directly in people with Hashimoto's):
· Normal follicles: a sudden load of iodine → Wolff-Chaikoff effect (iodine self-inhibition) → the follicle briefly cuts output → adaptive escape within days → recovery · Damaged Hashimoto's follicles: may fail to escape → sustained low → chronically raised · TPO oxidizing iodine itself creates oxidative stress; when the gland is already inflamed and short of GPx, more iodine may mean more injured cells and more self-fragments exposed to the immune system
Therefore:
· Hashimoto's + everyday diet: keep using iodized salt, and occasional seafood is fine; what to avoid is daily handfuls of kelp or nori and long-term high-dose iodine tablets (and tell your doctor about iodine-containing cough syrups or iodinated contrast) · Hashimoto's + pregnancy: do not stop iodine (the fetus needs it); the ATA suggests a 150 µg/day supplement on top of diet in pregnancy, and no more · Inland, almost no seafood: rely on iodized salt to cover 150 µg a day (the US adult ) · The idea that Hashimoto's means cutting out iodine completely goes too far
Two iodine numbers: adult RDA 150 µg/day; tolerable upper intake level () 1100 µg/day — a long-term ceiling, not a target
Follow-up: check TSH and free T4 regularly, at intervals your doctor sets; if TSH rises and there are symptoms, discuss levothyroxine with endocrinology; whether to take selenium is also a question for the doctor first
One nutrient ≠ one answer: Hashimoto's is an immune disease, not a nutrient-deficiency disease. Nutrition (Se + adequate I + D + Fe) is supportive, not a cure.