Hardly any organ is linked to nutrients as often as the thyroid. Some of it is well documented, a larger part is marketing.
Here you will see which nutrients are actually involved physiologically, what may legally be said about them and where supplementing makes sense and where it does not.
Which nutrients are involved at all?
The thyroid needs several building blocks at the same time to do its work. If one is missing, an excess of the others does little.
| Nutrient | Role in thyroid metabolism |
|---|---|
| Iodine | Built directly into T4 and T3 |
| Selenium | Component of the enzymes that convert T4 into T3 and protect the tissue |
| Tyrosine | Amino acid, forms the backbone of both hormones |
| Iron | Component of the enzyme that attaches iodine to the backbone |
| Zinc | Involved in building the hormone receptors |
| Vitamin A | Involved in binding the hormone to its receptor in the cell nucleus |
How the individual steps of hormone production work is described in detail in our article What does the thyroid do?
Selenium: nowhere in the body is the concentration higher
Per gram of tissue, the thyroid contains more selenium than any other organ. This is no coincidence, there are two concrete reasons for it.
First, the conversion. The enzymes that turn the storage hormone T4 into active T3 are called deiodinases. They are selenoproteins, meaning they contain selenium as a fixed component. Without selenium, this conversion step does not work properly.
Second, protection. Hormone production inevitably generates hydrogen peroxide. The molecule is needed to incorporate iodine in the first place, but at the same time it attacks the surrounding tissue. The thyroid has its own protective system against this: the glutathione peroxidases. They are selenoproteins too.
So the thyroid runs a chemically aggressive process and needs selenium twice over, once for production and once for self-protection.
This is also why selenium is one of the few nutrients for which a thyroid-related claim is officially authorised. The approved wording according to the EU list, which also shapes Swiss practice, is: Selenium contributes to normal thyroid function. Also authorised are the claims on protecting cells from oxidative stress, on the immune system and on the maintenance of normal hair and nails.
Why selenium is a topic in Switzerland
How much selenium a food contains depends on the soil it grew in. Swiss soils are low in selenium, as are European soils in general. Grain grown in Switzerland therefore supplies little selenium. Animal feed, on the other hand, may be enriched, which is why meat, eggs, dairy products and fish are the reliable sources of selenium here.
Selenium-poor soils still do not mean selenium-poor people. The Federal Food Safety and Veterinary Office has been monitoring selenium status for more than 25 years and finds insufficient intake in fewer than 2 percent of men and fewer than 5 percent of women. Imports and enriched feed usually make up for it.
Iodine: the building block without which nothing works
Iodine is the only nutrient that physically becomes part of the hormone. T4 carries four iodine atoms, T3 three.
Here too there is an authorised claim: Iodine contributes to the normal production of thyroid hormones and normal thyroid function.
The same applies to iodine as to selenium, only more pronounced: both too little and too much disturb function. If you already use iodised table salt and regularly eat dairy products or sea fish, you are usually within range. Taking high-dose iodine supplements on suspicion is not a good idea.
Iron, zinc and tyrosine
Iron is a component of thyroid peroxidase. This enzyme attaches the iodine atoms to the backbone, and it contains heme, an iron-containing group. In Switzerland, iron deficiency is common mainly among women of childbearing age. Whether it is present is shown by a ferritin value in the blood, not by a feeling.
Zinc is involved in the structural build-up of the receptors through which thyroid hormones act in the cell. Without a suitable receptor, the hormone that is present is of little use.
Tyrosine is the amino acid the hormone backbone is made of. It is not essential, the body can produce it from phenylalanine. With normal protein intake, tyrosine is therefore rarely a bottleneck, even if it appears prominently on many labels.
Vitamin A and vitamin B12: what is true
Precision matters here, because online far more is claimed about both than can be proven.
Vitamin A plays a role in the mechanism through which thyroid hormones act in the cell nucleus. There, the receptor for thyroid hormones works as a pair with a second receptor, and this second one responds to a form of vitamin A. That is established cell biology. Even so, there is no authorised health claim on vitamin A and the thyroid. The recognised claims concern vision, the immune system, skin, mucous membranes and iron metabolism.
Vitamin B12 has nothing directly to do with hormone production. The link is indirect: in autoimmune thyroid diseases, B12 deficiency occurs statistically more often than in the general population. Both conditions have an autoimmune component and often occur together. This is an observed association, not a cause and effect relationship. A B12 deficiency does not cause thyroid disease, and B12 does not fix one.
The practical conclusion: both are important nutrients with good reasons for an adequate supply. As a targeted thyroid measure, they are not suitable.
What "support" realistically means
Under terms such as thyroid support, products are sold online whose promises go far beyond what is permissible or tenable.
The sober assessment: nutrients can make sure the thyroid has what it needs for its normal function. Nothing more.
Just as important: supplementing a nutrient that is not lacking brings no additional benefit. With selenium and iodine it can even do harm. The sensible route is a blood test, not a product.
Where these nutrients occur in food
Most people cover their needs through their diet without thinking about it.
Selenium is found in fish and seafood, in eggs, in meat and offal, and in Brazil nuts, although their content varies greatly. Red meat and liver provide iron in a particularly well usable form. Zinc is found in meat, cheese and shellfish. Vitamin A in the form of directly usable retinol occurs almost only in animal foods, above all liver. Vitamin B12 is found exclusively in animal foods.
It is striking how often organ meat appears in this list. Liver and kidney are among the most nutrient-dense foods of all, yet hardly play a role in today's cooking. If you avoid the taste, you can also find liver in freeze-dried form, for example in our organic beef liver capsules from Estonian pasture farming. It remains a food and replaces neither a balanced diet nor medical treatment.
What dried thyroid tissue as a product category of its own is all about, and where the line to medicinal products runs, we explain in our article on natural thyroid extract.
Frequently asked questions
What role does selenium play for the thyroid?
Selenium is a component of the enzymes that convert T4 into active T3, and of the enzymes that protect the tissue from the hydrogen peroxide produced during hormone production. The authorised claim is that selenium contributes to normal thyroid function.
How much selenium per day makes sense?
The reference values are around 60 micrograms for women and 70 micrograms for men per day. EFSA states 255 micrograms per day as the tolerable total intake from all sources.
Can too much selenium be harmful?
Yes. Selenium has a narrow window between deficiency and excess. A permanently excessive intake can cause hair loss, brittle nails, gastrointestinal complaints and garlic-like breath.
Which vitamins does the thyroid need?
What matters most are the trace elements iodine and selenium, not vitamins. Vitamin A is involved in the mechanism by which the hormones act in the cell nucleus. There is no authorised thyroid-related claim for vitamins.
Does vitamin B12 have anything to do with the thyroid?
Only indirectly. B12 deficiency occurs more often in autoimmune thyroid diseases because both conditions have an autoimmune component. There is no cause and effect relationship.
Which trace elements are important for the thyroid?
Iodine as a building block of the hormones, selenium for conversion and cell protection, iron as a component of the iodine-incorporating enzyme and zinc for building the hormone receptors.
Should I supplement nutrients on suspicion?
No. Supplementing a nutrient that is not lacking brings no benefit, and with iodine and selenium it can do harm. A blood test clarifies whether there is a deficiency at all.