Nutrients for an Underactive Thyroid: Iodine, Selenium & More

Constant tiredness, feeling cold, dry skin, a sense of inner sluggishness – anyone familiar with these complaints often ends up looking at the thyroid when searching for a cause. An underactive thyroid is common, and plenty of advice about diet and nutrients circulates around it. But which nutrients actually have a proven link to the thyroid – and where does sensible support end and risky self-treatment begin? That's exactly what this guide addresses.

What happens with an underactive thyroid

The thyroid is a small, butterfly-shaped gland in the neck. It produces the hormones thyroxine (T4) and triiodothyronine (T3), which regulate metabolism in almost every cell in the body – from body temperature to heart rate to concentration. With an underactive thyroid (medically, hypothyroidism), the gland produces too little of these hormones. The entire metabolism then runs more slowly, which explains typical complaints such as fatigue, lack of drive, feeling cold, weight gain and dry skin.

The most common cause of an underactive thyroid in Germany is Hashimoto's thyroiditis – a chronic inflammation in which the immune system mistakenly attacks the body's own thyroid tissue. Over the years this can reduce the gland's hormone-producing capacity. Because Hashimoto's is an autoimmune disease, there are some special considerations around nutrients here – particularly iodine – which we address further below.

It's important to understand that an underactive thyroid can develop gradually over months and years, which is why the symptoms are often nonspecific at first and easily attributed to other causes. The opposite, an overactive thyroid, is also possible – for instance in early phases of Hashimoto's disease. That's exactly why judging things by symptoms alone is never sufficient, and only blood values give a reliable picture.

Diagnosis and medical treatment come first

The most important point up front, clear and unambiguous: an underactive thyroid needs to be medically assessed and treated. Whether an underactive thyroid is even present is only shown by a blood test (among other things TSH, often also fT4 and the antibodies). Based on these values, the doctor decides on therapy. In many cases, the standard is administering the thyroid hormone levothyroxine (L-thyroxine), which replaces the missing hormone amount.

This treatment cannot be replaced by any food or dietary supplement. Very important: an existing levothyroxine dose must never be changed, reduced or stopped on your own – that belongs exclusively in medical hands and is guided by follow-up values. Nutrients can support the body alongside this, but they are not a substitute for diagnosis and therapy. If you're unsure or have symptoms, get it medically assessed first.

Nutrients related to the thyroid

Some nutrients are genuinely relevant to the thyroid – and for two of them there are officially authorised health claims from the European Food Safety Authority (EFSA):

• Iodine is the central building block of thyroid hormones – without iodine, the gland simply cannot form them. The authorised claim reads: Iodine contributes to normal thyroid hormone production and normal thyroid function. Germany is considered a mild iodine-deficient region, which is why adequate intake is generally worth attention.
• Selenium is a component of enzymes involved in thyroid hormone metabolism. There is also an EU claim here: Selenium contributes to normal thyroid function.
• Zinc plays a role in many aspects of hormone metabolism and contributes, among other things, to normal cognitive function and normal macronutrient metabolism.
• Iron is important for the formation of red blood cells and oxygen transport; a deficiency can overlap with symptoms similar to an underactive thyroid (fatigue, exhaustion).
• Vitamin D is involved in normal function of the immune system. Vitamin D status is a frequently discussed topic, particularly with autoimmune conditions like Hashimoto's.

For a deeper look, see our overview on nutrients for the thyroid as well as specifically the interplay of iodine and selenium for the thyroid.

Caution with iodine in Hashimoto's

This point deserves particular care – and it's often underestimated. With Hashimoto's thyroiditis, the autoimmune form, iodine is not simply "good" across the board. High iodine intakes can unfavourably influence the inflammatory process in an existing autoimmune thyroiditis. So the rule is: anyone with Hashimoto's should only take higher-dose iodine supplements after explicit consultation with a doctor – not on their own initiative.

This doesn't mean iodine from normal food suddenly becomes harmful; the usual diet including iodised table salt isn't what's meant here. This is about targeted, higher-dose supplementation. Because the line between sensible and unfavourable runs individually here and depends on the specific blood values and diagnosis, medical clarification before iodine supplementation in Hashimoto's is essential. What else matters when choosing a supplement is summarised in our guide buying iodine: what to look for.

A diet that supports the thyroid

Alongside individual nutrients, the overall picture on your plate matters. A balanced, wholesome diet usually provides the relevant building blocks almost automatically:

• Saltwater fish (such as cod or coley) provides iodine and is often cited as a natural iodine source.
• Brazil nuts are among the most selenium-rich foods – just a few nuts cover a large part of the requirement; because of this high density, moderation is more the order of the day here.
• Iodised table salt is a simple everyday base source of iodine in Germany.
• Whole grains, legumes, nuts and seeds contribute zinc and iron.
• Vegetables, fruit and quality fats round out the supply of vitamins and secondary plant compounds.

A frequently raised topic is so-called goitrogenic (goitre-forming) substances in raw cabbage vegetables. In the amounts typical here, and when cooked, they play no practical role for most people – so nothing speaks against a colourful vegetable-rich diet. More important than avoiding individual foods is an overall varied diet.

Another practical point concerns absorption: certain nutrients and supplements can affect each other. For example, it's known that the absorption of levothyroxine can be impaired by simultaneous intake of calcium- or iron-rich supplements. That's why levothyroxine is usually taken on an empty stomach, with a time gap from such supplements and meals. If you use dietary supplements, it's best to discuss the right timing with your treating practice so therapy and supplementation don't get in each other's way.

An honest take

Nutrients are no substitute for the medical treatment of an underactive thyroid – that can't be emphasised enough. Anyone with a diagnosed underactive thyroid will generally manage it well with medically adjusted therapy. What an adequate nutrient supply can do is support the body's normal functions: as cited above, iodine and selenium have a scientifically recognised link to normal thyroid function.

At the same time: more is not automatically better. Especially with iodine and autoimmune thyroiditis, too high an intake can have the opposite effect. The most sensible path is therefore to get symptoms medically assessed, know your blood values, and coordinate any supplementation with your treating practice. That way, nutrient supply stays a sensible building block – not a risk.

Bottom line, a sober view pays off: the thyroid reacts sensitively to both over- and under-supply. Anyone who eats a balanced diet, knows their values, and coordinates supplements with their treating practice takes the path that offers the most security in the long run – without blind activism and without false promises.

Matching products from Scheunengut

If you want to specifically support your thyroid with the two most relevant trace elements, take a look at our Thyroid Intenso Iodine-Selenium Complex – a supplement that combines iodine and selenium and is rounded off with thyme. Iodine contributes to normal thyroid hormone production and normal thyroid function, selenium to normal thyroid function. Please note the points on Hashimoto's above: with autoimmune thyroiditis or an existing thyroid condition, discuss taking iodine-containing supplements with your doctor first.

Frequently asked questions

Which nutrients are important with an underactive thyroid?

The focus is on iodine and selenium, for which there are authorised EU claims regarding normal thyroid function. Zinc, iron and vitamin D are also frequently mentioned in connection with the thyroid. What remains decisive, however, is the medical treatment of the underactive thyroid itself.

Can I simply take iodine with Hashimoto's?

No. With Hashimoto's thyroiditis, higher-dose iodine supplements can unfavourably influence the autoimmune process. Targeted iodine supplementation should therefore only happen after explicit consultation with a doctor. Iodine from a normal diet with iodised salt is not what's meant here.

Does selenium or iodine replace taking levothyroxine?

No. Levothyroxine replaces missing thyroid hormones and is medically adjusted. Nutrients cannot replace this therapy. A prescribed levothyroxine dose must never be changed or stopped on your own.

Does a particular diet help with an underactive thyroid?

A balanced, wholesome diet usually provides the relevant building blocks like iodine, selenium, zinc and iron almost automatically. It supports normal supply but is no substitute for the medical treatment of the underactive thyroid.

Are Brazil nuts a sensible selenium source?

Brazil nuts are among the most selenium-rich foods; just a few nuts provide a lot of selenium. Because of this high density, moderation makes more sense than eating large amounts. If you want to supplement in a targeted way, pay attention to an appropriate dosage.

When should I see a doctor?

With persistent tiredness, feeling cold, weight changes or other symptoms, a medical assessment with a blood test is worthwhile. Only that can determine whether an underactive thyroid is present and which treatment makes sense.