Iodine is an essential trace element that is indispensable for the production of thyroid hormones. But especially with autoimmune diseases of the thyroid such as Hashimoto’s thyroiditis, there is great uncertainty: Is iodine helpful or harmful? The answer is more complex than a simple yes or no – and depends on various factors that we will examine in this article.
The Role of Iodine in the Body
Iodine is a vital trace element that the body cannot produce itself. It must be obtained through food. The thyroid gland needs iodine to produce the hormones thyroxine (T4) and triiodothyronine (T3), which influence almost every cell in the body. These hormones regulate metabolism, body temperature, the cardiovascular system, the nervous system, and are particularly important for brain development in children.
According to nutritional guidelines, a healthy adult needs about 150 micrograms of iodine daily. Pregnant and breastfeeding women have an increased requirement of 220 to 290 micrograms. Many countries are considered iodine-deficient areas, which is why the use of iodized table salt has been recommended for decades.
Iodine Deficiency and Its Consequences
Chronic iodine deficiency means the thyroid cannot produce sufficient hormones. As a compensation mechanism, the thyroid enlarges – a goiter (struma) develops. Other consequences can include hypothyroidism, fatigue, weight gain, concentration problems, and in pregnant women, serious developmental disorders in the unborn child.
Hashimoto’s Thyroiditis: When the Immune System Attacks the Thyroid
Hashimoto’s thyroiditis is the most common cause of hypothyroidism in industrialized countries. In this autoimmune disease, the immune system mistakenly attacks the body’s own thyroid tissue. Antibodies, particularly TPO antibodies (against thyroid peroxidase) and Tg antibodies (against thyroglobulin), gradually destroy thyroid cells.
Over the course of the disease, the thyroid’s ability to produce hormones decreases, leading to hypothyroidism. Typical symptoms include fatigue, weight gain, cold sensitivity, dry skin, hair loss, constipation, and depressive moods. The disease often progresses in episodes and can significantly impair quality of life over years.
The Iodine Controversy in Hashimoto’s
This is where the controversy begins: While iodine is essential for healthy thyroid function, there is evidence that excessive iodine intake in people with Hashimoto’s thyroiditis can intensify the autoimmune reaction. Studies show that in countries with high iodine intake, the prevalence of autoimmune thyroid diseases is higher than in iodine-deficient areas.
The mechanism behind this: Iodine increases the immunogenicity of thyroglobulin, a protein in the thyroid. In people with a genetic predisposition to autoimmune diseases, this can activate the immune system and lead to antibody formation. Additionally, excess iodine can cause oxidative stress in the thyroid, further fueling the inflammatory reaction.
The Scientific Evidence: What Do Studies Say?
The research on iodine and Hashimoto’s is nuanced. Several studies from Asia, where iodine intake is traditionally higher, show a connection between high iodine consumption and elevated thyroid antibodies. A Chinese study found that people with a daily iodine intake of over 800 micrograms had a significantly increased risk of Hashimoto’s.
On the other hand, research also shows that iodine deficiency is problematic. An Italian study found that Hashimoto’s patients with iodine deficiency had more severe symptoms and higher antibody levels than those with adequate iodine supply. The problem therefore lies not in iodine itself, but in the dosage.
The Goldilocks Principle: Not Too Much, Not Too Little
Current scientific findings suggest a U-shaped curve: both too little and too much iodine can be problematic in Hashimoto’s. The optimal range is about 150 to 300 micrograms daily – enough to support thyroid function, but not so much as to fuel the autoimmune reaction.
Practical Recommendations for Hashimoto’s Patients
For people with Hashimoto’s thyroiditis, conscious management of iodine is important. Here are evidence-based recommendations:
Determine Iodine Status
Before changing your iodine intake, you should have your current iodine status checked. This is most reliably done through a 24-hour urine collection that measures iodine excretion. Alternatively, a morning urine test can provide clues, but is less precise. Determining selenium levels in the blood is also useful, as selenium is important for iodine metabolism.
Moderate Iodine Intake Through Natural Sources
Instead of high-dose iodine supplements, Hashimoto’s patients should rely on moderate intake through natural foods. Good iodine sources are seafood (2-3 times per week), dairy products in moderation, eggs, and iodized table salt in normal amounts. Caution is advised with algae and seaweed, which can contain extremely high amounts of iodine – sometimes several thousand micrograms per serving.
Avoid High-Dose Iodine Supplements
Dietary supplements with more than 500 micrograms of iodine per daily dose should be avoided with Hashimoto’s. Even supposedly natural products like kelp capsules or spirulina can contain problematically high amounts of iodine. If supplementation is necessary, it should only be done under medical supervision and with regular monitoring of thyroid values and antibodies.
Selenium as an Important Cofactor
Selenium plays a central role in thyroid metabolism. It is a component of enzymes that activate thyroid hormones and protect the thyroid from oxidative stress. Studies show that selenium supplementation (200 micrograms daily) in Hashimoto’s patients can lower antibody levels and improve thyroid function. Selenium also appears to mitigate the negative effects of excess iodine.
Special Situations: Pregnancy and Breastfeeding
During pregnancy and breastfeeding, adequate iodine supply is particularly important, as iodine deficiency can lead to serious developmental disorders in the child. Even women with Hashimoto’s should not avoid iodine during this time. The recommended intake is 220 micrograms during pregnancy and 290 micrograms during breastfeeding.
However, it’s important that thyroid values are closely monitored, as hormone requirements change during pregnancy. The dosage of levothyroxine often needs to be adjusted. An iodine tablet with 100 to 150 micrograms in addition to normal diet is recommended by professional societies, but should be coordinated with the treating physician.
Other Thyroid Diseases and Iodine
Graves’ Disease
With Graves’ disease, another autoimmune disease of the thyroid that leads to hyperthyroidism, the situation is different. Here, iodine should be avoided in the acute phase, as it can further boost hormone production. After successful treatment of hyperthyroidism, similar recommendations apply as with Hashimoto’s.
Thyroid Nodules and Autonomous Adenomas
With hot nodules (autonomous adenomas) that produce hormones uncontrollably, a suddenly high iodine intake can trigger a thyrotoxic crisis. People with known thyroid nodules should have their thyroid function checked before taking iodine-containing medications or contrast agents.
Iodine-Containing Medications and Contrast Agents
Special caution is required with iodine-containing medications such as amiodarone (a heart medication) or iodine-containing X-ray contrast agents. These can contain extremely high amounts of iodine – a CT scan with contrast agent can deliver up to 15,000 micrograms of iodine. In Hashimoto’s patients, this can lead to a worsening of the autoimmune reaction or to functional disorders.
If an examination with contrast agent is necessary, thyroid values should be checked before and after. In some cases, a temporary adjustment of thyroid medication may be necessary.
Nutritional Strategies: Finding the Right Balance
A balanced diet can help keep iodine intake in the optimal range. Here are some practical tips:
Use iodized table salt in normal amounts (about 5 grams per day corresponds to 100 micrograms of iodine). Eat seafood 2-3 times per week such as cod, pollock, or plaice. One serving provides about 100-200 micrograms of iodine. Dairy products also contain iodine, although in varying amounts – a glass of milk contains about 40-80 micrograms.
Avoid algae products such as nori, wakame, or kombu, unless the iodine content is clearly declared and low. Many algae contain several thousand micrograms of iodine per serving. Also check the ingredient list on processed foods – some contain algae additives or carrageenan.
Monitoring and Medical Supervision
People with Hashimoto’s should have their thyroid values checked regularly. This includes TSH, fT3, fT4, and antibodies (TPO-Ab and Tg-Ab). When changing iodine intake or diet, values should be checked after 6-8 weeks, as changes often appear delayed.
Symptoms are also important: worsening fatigue, weight gain, hair loss, or mood swings can indicate hypothyroidism. Nervousness, rapid heartbeat, weight loss, or increased sweating can be signs of hyperthyroidism and should be medically evaluated.
Conclusion: Iodine in Hashimoto’s – An Individual Decision
The question of whether iodine is friend or foe in Hashimoto’s cannot be answered universally. Scientific evidence shows: both iodine deficiency and iodine excess can be problematic. The key lies in the right dosage – in the optimal range of about 150 to 300 micrograms daily.
Hashimoto’s patients should neither completely avoid iodine nor take high-dose supplements. Moderate intake through natural foods, combined with adequate selenium supply, is the most sensible approach. Individual adaptation is particularly important: what is optimal for one patient may be too much or too little for another.
Have your iodine status determined, work closely with your doctor, and pay attention to your body’s signals. With the right amount of iodine, the thyroid can be optimally supported without fueling the autoimmune reaction. Iodine is neither fundamentally friend nor foe – it depends on the dose and individual situation.