The thyroid gland — that butterfly-shaped organ sitting at the base of the neck — has an outsized influence on nearly every system in the body. Thyroid hormones regulate metabolism, body temperature, heart rate, mood, digestion, and even skin and hair health. When the thyroid isn't functioning optimally, the consequences can range from chronic fatigue and weight gain to depression, brain fog, and cardiovascular complications.
Thyroid disorders are among the most common endocrine conditions in Ireland. Hypothyroidism (underactive thyroid) is estimated to affect up to 5% of the Irish population, with many more experiencing subclinical dysfunction that doesn't yet meet the diagnostic threshold. Women are significantly more affected than men. At The Honey Pot in Clonmel, naturopath Pat Coffey regularly sees clients asking about nutritional support for thyroid health — this guide outlines the key considerations.
The thyroid produces two main hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the storage form, converted in the liver, kidneys, and other tissues to the more active T3. This conversion process is nutritionally dependent — it requires specific minerals and cofactors to work properly.
The thyroid's production of hormones is regulated by Thyroid Stimulating Hormone (TSH) from the pituitary gland, which itself is regulated by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus. This feedback loop can be disrupted by nutritional deficiencies, environmental toxins, chronic stress, and autoimmune activity (as in Hashimoto's thyroiditis).
Iodine is the primary raw material from which thyroid hormones are made. Without adequate iodine, the thyroid simply cannot produce enough T4 and T3. Iodine deficiency is the most common cause of thyroid disorders globally, and while severe deficiency is rare in Ireland, mild to moderate insufficiency is more common than many people realise.
The main dietary sources of iodine in the Irish diet are:
People following plant-based diets in Ireland are at particular risk of iodine insufficiency, as dairy — the main source — is excluded. An iodine supplement or iodine-containing multivitamin is generally recommended for vegans.
Important: Iodine supplementation should be approached carefully. Both too little and too much iodine can negatively affect thyroid function. Those with existing thyroid conditions (particularly Hashimoto's thyroiditis) should consult their GP before supplementing with iodine.
Ireland has a remarkable coastline rich in seaweed, and kelp (Laminaria species) has been harvested along Irish shores for centuries. Kelp is one of the richest natural sources of iodine — but this is also why it needs to be treated with respect. The iodine content in kelp products can vary enormously, and some products can provide very high doses that may actually worsen thyroid function in susceptible individuals.
If choosing a kelp supplement, look for products that list the actual iodine content per dose and ensure it falls within the recommended range (roughly 150–300 mcg/day for adults, well below the upper tolerable limit of 600 mcg/day set by the EU). Pat Coffey advises caution with kelp products whose iodine content is unspecified.
Selenium is arguably just as important as iodine for thyroid function, though far less talked about. It is required for:
Selenium content in Irish soils is generally low — Irish crops and grasses tend to reflect this deficiency, meaning the Irish diet is frequently low in selenium compared to, say, North American diets. Brazil nuts are the richest food source (just 2–3 per day provides adequate selenium), or a supplement of 100–200 mcg of selenium (preferably in the organic selenomethionine form) is commonly recommended by naturopaths.
Vitamin B12 deficiency is more common in people with autoimmune thyroid conditions (Hashimoto's and Graves' disease) than in the general population — possibly because autoimmune conditions can affect the gut's ability to produce intrinsic factor (needed for B12 absorption). B12 deficiency shares many symptoms with hypothyroidism, including fatigue, brain fog, and low mood, potentially compounding the problem.
Regular B12 testing is worthwhile for anyone with thyroid autoimmunity. Methylcobalamin (the active, methylated form of B12) is generally preferred to cyanocobalamin in supplemental form. Sublingual B12 drops or sprays can be useful for those with absorption issues.
Zinc is required for the synthesis of thyroid hormone and also plays a role in the conversion of T4 to T3. Low zinc is associated with reduced thyroid function. Good dietary sources include meat, shellfish (oysters are exceptionally rich), pumpkin seeds, and legumes.
Iron is needed for the enzyme thyroid peroxidase, which is essential in the first step of thyroid hormone production. Iron deficiency anaemia — relatively common in Irish women of reproductive age — can impair thyroid function and reduce the effectiveness of thyroid medication. If you're experiencing significant fatigue alongside thyroid symptoms, ask your GP to check both thyroid markers and iron/ferritin levels.
Hashimoto's thyroiditis is an autoimmune condition in which the immune system attacks the thyroid gland, and it's by far the most common cause of hypothyroidism in Ireland. Research consistently shows that people with Hashimoto's tend to have lower Vitamin D levels than the general population, and some studies have found that Vitamin D supplementation may help reduce thyroid antibody levels.
Given that Vitamin D deficiency is already endemic in Ireland due to limited sunshine, supplementation is sensible for virtually everyone — and perhaps especially important for those with Hashimoto's or other autoimmune thyroid conditions.
Some foods contain compounds called goitrogens that, in very large quantities, may interfere with iodine uptake by the thyroid. These include raw brassica vegetables (cabbage, kale, broccoli, Brussels sprouts). Cooking largely deactivates goitrins. In realistic dietary amounts, these vegetables are beneficial for overall health — there is no need to avoid them unless advised specifically by a healthcare professional managing a thyroid condition.
Similarly, soy isoflavones have shown some goitrogenic activity in research, particularly when iodine intake is borderline. People taking levothyroxine (thyroid medication) are advised to leave at least four hours between their medication and soy-containing foods or supplements.
Thyroid health is a medical matter requiring proper diagnosis and monitoring. The information in this guide is educational and not a substitute for medical advice or thyroid function testing. Please see your GP if you experience:
Thyroid function (TSH, free T4, and ideally free T3 and thyroid antibodies) should be assessed by blood test. Never self-diagnose or self-treat thyroid conditions — iodine supplementation in particular can worsen autoimmune thyroid disease if used inappropriately. The HSE provides thyroid information at hse.ie. Always inform your GP and pharmacist of any supplements you are taking, particularly if you are on levothyroxine.
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