Iodine deficiency: causes, symptoms, foods, treatment and prevention

Iodine is needed in only small amounts, but its role in the body is anything but small. The thyroid gland uses iodine to produce thyroid hormones, which influence metabolism, energy use, growth, brain development and many other important processes. When the body does not get enough iodine over time, thyroid hormone production can be affected, potentially leading to hypothyroidism and an enlarged thyroid, known as a goitre.

Iodine deficiency is particularly important during pregnancy and early childhood because thyroid hormones are essential for normal brain and nervous system development. People who eat little or no seafood, dairy or eggs, including some vegetarians and vegans, may also have a higher risk of inadequate iodine intake.

The good news is that iodine deficiency is often preventable. A balanced diet, appropriate use of iodised salt and supplementation when medically recommended can help maintain adequate iodine intake.

What is iodine deficiency?

Iodine deficiency occurs when dietary iodine intake is insufficient to meet the body’s needs. Because iodine is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), inadequate iodine can eventually interfere with thyroid hormone production.

When thyroid hormone production falls, the pituitary gland may respond by producing more thyroid-stimulating hormone (TSH). Higher TSH encourages the thyroid to work harder and capture more iodine from the bloodstream. Over time, this stimulation can contribute to thyroid enlargement or goitre.

However, iodine deficiency does not always cause obvious symptoms. Mild deficiency can go unnoticed, which is one reason dietary intake and risk factors are important when assessing iodine status.

The World Health Organization considers iodine deficiency an important nutritional problem because insufficient iodine can affect thyroid function, growth and neurodevelopment, particularly in vulnerable groups.

What are the causes of iodine deficiency?

The most common cause is simply not getting enough iodine through the diet. However, several factors can make this more likely.

Low dietary iodine intake

People who rarely eat iodine-containing foods may gradually develop inadequate intake. Seafood, dairy products, eggs and iodised salt are among the more reliable dietary sources.

Using only non-iodised salt can also reduce iodine intake. In India, the National Iodine Deficiency Disorders Control Programme promotes iodised salt as an important strategy for preventing iodine deficiency.

Vegetarian or vegan diets

A vegetarian diet is not automatically deficient in iodine. However, people who avoid seafood, eggs and dairy products need to plan their diet more carefully because several commonly eaten plant foods contain relatively little iodine. Vegans may therefore be at greater risk if they do not regularly consume iodised salt or iodine-fortified foods.

Pregnancy and breastfeeding

Iodine requirements increase during pregnancy and breastfeeding. The thyroid has greater demands during pregnancy, while iodine is also important for fetal brain and nervous system development. Breastfeeding mothers need enough iodine to provide iodine through breast milk.

Living in an iodine-deficient region

The amount of iodine in soil varies considerably. Crops grown in iodine-poor soil may contain relatively little iodine. This can influence the iodine content of a predominantly plant-based diet.

Restrictive diets

People who avoid several food groups because of allergies, lactose intolerance, dietary preferences or other restrictions may unintentionally reduce their iodine intake.

Excessive intake of certain goitrogenic foods in the setting of iodine deficiency

Certain foods contain compounds called goitrogens that can interfere with iodine uptake or thyroid hormone production. Examples include cassava, soy and some cruciferous vegetables such as cabbage, broccoli and cauliflower. However, this does not mean that healthy people should avoid these nutritious foods. The concern is greater when iodine intake is already inadequate or when very large amounts are consumed regularly.

What are the symptoms of iodine deficiency?

Mild iodine deficiency may cause no noticeable symptoms. As deficiency becomes more significant and thyroid hormone production is affected, symptoms may resemble hypothyroidism.

Possible symptoms include:

• Tiredness and low energy
• Feeling unusually cold
• Unexplained weight gain
• Constipation
• Dry skin
• Reduced concentration
• Low mood
• A slower heart rate
• Difficulty maintaining normal body temperature
• Thyroid enlargement or a swelling in the neck

Healthdirect notes that hypothyroidism caused by iodine deficiency can produce symptoms such as tiredness, feeling cold, weight gain and constipation.

A goitre may develop because the thyroid is being continuously stimulated to produce more thyroid hormone. However, a neck swelling can have many causes, so it should not automatically be assumed to be due to iodine deficiency.

How is iodine deficiency diagnosed?

There is no single test that should be used in isolation to diagnose iodine deficiency in every individual.

Urinary iodine is widely used to assess iodine status, particularly at the population level. Because most absorbed iodine is eventually excreted in urine, urinary iodine reflects recent iodine intake. However, a single spot urine sample can fluctuate considerably and is not ideal for diagnosing an individual person.

A doctor may also evaluate thyroid function with blood tests such as TSH and free T4. A thyroid ultrasound may be recommended if there is thyroid enlargement or a suspected thyroid nodule.

Importantly, a normal TSH does not completely rule out inadequate iodine intake. TSH is not a particularly sensitive standalone marker of iodine deficiency.

How can I increase my iodine levels?

The safest approach is usually to improve dietary iodine intake rather than immediately starting a high-dose supplement.

Consider:

1. Using iodised salt instead of ordinary non-iodised salt, while still keeping total salt intake within recommended limits.
2. Including iodine-rich foods such as seafood, dairy and eggs if they fit your diet.
3. Choosing an iodine-fortified food or beverage when available.
4. If you are vegetarian or vegan, deliberately including reliable iodine sources rather than assuming that plant foods provide enough.
5. Discussing an iodine supplement with your doctor if your diet is insufficient or you have increased requirements.

WHO identifies salt iodisation as an effective strategy for preventing iodine deficiency at the population level.

How do I increase my iodine naturally?

Food is generally the best place to start.

Good natural sources include seafood, fish, eggs and dairy products. Seaweed can also contain very high amounts of iodine, but its iodine content varies dramatically between species and products. For this reason, eating large amounts of kelp or seaweed specifically to “boost iodine” can actually result in excessive intake.

For people who eat dairy and eggs, regularly including these foods alongside iodised salt can make it easier to meet iodine requirements.

For vegans, iodised salt and appropriately fortified foods are particularly useful because most fruits and vegetables naturally contain relatively little iodine.

What are 5 foods rich in iodine?

Five useful iodine-containing foods are:

1. Seaweed – Kelp, nori, kombu and wakame can be extremely rich in iodine. However, the amount varies widely, so moderation is important.
2. Fish and seafood – Cod, oysters, prawns and other seafood can provide substantial amounts of iodine.
3. Milk – Dairy milk is a useful source of iodine.
4. Yoghurt – Dairy yoghurt can contribute meaningful amounts of iodine.
5. Eggs – Eggs provide iodine and are particularly useful for people who do not eat seafood.

The exact iodine content of food varies according to growing conditions, animal feed, processing and other factors.

What drink has iodine in it?

Milk is one of the better-known drinks that naturally provides iodine. Dairy milk can contain a meaningful amount of iodine, although the exact amount varies.

Some fortified plant-based drinks may contain iodine, but this cannot be assumed. Always check the nutrition label or ingredient list because many plant-based beverages contain little iodine.

This is particularly relevant for vegans who have replaced dairy milk with soy, almond, oat or other plant-based drinks. Unless the product is fortified with iodine, it may not provide a useful amount.

What foods are low in iodine?

Many naturally plant-based foods are relatively low in iodine, including most fresh fruits and vegetables. Some grains, rice, pulses and unsalted nuts may also contain little iodine, although their iodine content can vary depending on soil and processing.

Examples of foods that can be relatively low in iodine include:

• Fresh fruits
• Most fresh vegetables
• Rice
• Unsalted nuts
• Pulses and legumes
• Non-iodised salt
• Some unfortified plant-based milk alternatives

There is an important distinction here: a low-iodine food is not necessarily a food you should avoid.

A medically prescribed low-iodine diet is usually used for specific situations, such as preparing for radioactive iodine treatment for certain thyroid conditions. It should not be followed simply because you are worried about iodine deficiency.

What foods block iodine absorption?

Foods containing goitrogenic compounds can interfere with iodine uptake or thyroid hormone production, particularly when iodine intake is already low.

Examples include:

• Soy and some soy products
• Cassava
• Cabbage
• Broccoli
• Cauliflower
• Kale
• Turnips
• Millet

However, this does not mean you need to eliminate broccoli, cabbage or soy from your diet. Evidence suggests that reasonable amounts of these foods are generally not a problem for people with adequate iodine intake.

The bigger concern is a combination of low iodine intake plus very high consumption of goitrogenic foods.

Cooking can also reduce some goitrogenic compounds. More importantly, maintaining adequate iodine intake makes dietary goitrogens much less concerning for most people.

How to get enough iodine as a vegetarian?

Vegetarians can absolutely meet their iodine requirements, but they need to pay attention to their food choices.

If you eat dairy and eggs, include foods such as:

• Milk
• Curd or yoghurt
• Cheese
• Eggs
• Iodised salt

If you are vegan, the challenge is greater because seafood, eggs and dairy are major dietary sources of iodine. In that situation, iodised salt and appropriately iodine-fortified foods or supplements may be needed.

Do not assume that Himalayan salt, rock salt or sea salt automatically provides iodine. Many specialty salts are not iodised. The label should specifically indicate that the salt is iodised.

What is the best iodine supplement?

There is no single “best” iodine supplement for everyone.

When supplementation is appropriate, iodine is commonly provided as potassium iodide or sodium iodide. Many multivitamin and mineral supplements contain around 150 micrograms of iodine.

Potassium iodide is a well-established form of supplemental iodine. However, this does not mean everyone should start taking it.

Be particularly cautious with high-dose iodine products and kelp supplements. Seaweed products can contain highly variable amounts of iodine, and some iodine-only supplements contain doses that exceed the recommended upper limit.

For adults, the recommended intake is generally around 150 micrograms per day, while requirements are higher during pregnancy and breastfeeding. The NIH lists an upper intake level of 1,100 micrograms per day for adults, although medical treatment can involve different amounts under professional supervision.

Who should avoid taking iodine?

People with thyroid disorders should not start iodine supplements without medical advice.

Extra caution is particularly important if you have:

• Hyperthyroidism
• Graves’ disease
• Hashimoto’s thyroiditis or other autoimmune thyroid disease
• A thyroid nodule or multinodular goitre
• A history of iodine-induced thyroid problems
• Certain kidney or cardiovascular conditions requiring medicines that may interact with iodine

Iodine can interact with some medications, including antithyroid medicines, ACE inhibitors and potassium-sparing diuretics.

People preparing for radioactive iodine treatment may also be specifically instructed to follow a low-iodine diet. This is very different from treating iodine deficiency and should only be done according to the treating team’s instructions.

Can you take iodine and vitamin D together?

Generally, yes. There is no standard requirement to separate iodine and vitamin D supplements simply because they are being taken together.

However, taking multiple supplements does not automatically make them beneficial. Check the doses of each product, particularly if you are already taking a multivitamin, prenatal supplement or thyroid-related medication.

Vitamin D also has its own medication and supplement interactions, so anyone taking several medicines or high-dose supplements should review the combination with a doctor or pharmacist.

Does iodine raise TSH levels?

It can, but the relationship is more complicated than simply saying that iodine raises or lowers TSH.

When iodine intake is too low, thyroid hormone production may fall and TSH can rise as the pituitary attempts to stimulate the thyroid. Correcting an iodine deficiency can therefore help normalise thyroid function.

On the other hand, excess iodine can also increase TSH in some people and may trigger hypothyroidism or other thyroid dysfunction. Healthdirect specifically notes that excessive iodine can be associated with higher TSH levels, hypothyroidism, hyperthyroidism and thyroiditis.

This is why taking more iodine is not necessarily better. The goal is adequate iodine intake, not maximum iodine intake.

Can iodine deficiency be prevented?

For most people, prevention comes down to a balanced diet and a reliable source of iodine.

In India, the National Iodine Deficiency Disorders Control Programme promotes the use of iodised salt as a key public-health measure.

At home, check the salt packet to confirm that it is iodised. Store salt properly and avoid assuming that premium or specialty salts contain iodine.

If you are pregnant, planning pregnancy or breastfeeding, speak with your doctor about your iodine requirements. These life stages have higher iodine needs, and supplementation may be recommended depending on your circumstances and dietary intake.

When should you see a doctor?

Speak with a doctor if you have symptoms that could indicate thyroid dysfunction, especially persistent tiredness, unexplained weight changes, constipation, feeling unusually cold or swelling in the neck.

You should also seek medical advice before taking iodine supplements if you have an existing thyroid condition.

If iodine deficiency is suspected, your doctor may evaluate your diet, symptoms and thyroid function and decide whether urinary iodine testing or other investigations are appropriate.

Remember that symptoms such as tiredness and weight gain are not specific to iodine deficiency. Iron deficiency, vitamin deficiencies, thyroid disorders, sleep problems and many other conditions can cause similar symptoms.

Frequently asked questions about iodine deficiency

Is iodine deficiency serious?

It can be, particularly when deficiency is severe or occurs during pregnancy and early childhood. Severe iodine deficiency can impair thyroid hormone production and, during fetal development, can cause serious and potentially irreversible effects on brain development.

What is the fastest way to increase iodine?

The most practical approach is to use iodised salt appropriately and include iodine-rich foods such as dairy, eggs and seafood if they fit your diet. Supplements should be used when appropriate rather than taking high doses on your own.

Can I get enough iodine without eating fish?

Yes. Dairy products, eggs and iodised salt can provide iodine. Vegans may need to rely more heavily on iodised salt, fortified foods or a medically appropriate supplement.

Is seaweed the best source of iodine?

Seaweed can contain extremely high amounts of iodine, but its iodine content varies considerably. More is not necessarily better, so large quantities of kelp or seaweed supplements are not recommended simply to increase iodine intake.

Does iodine deficiency always cause hypothyroidism?

No. Mild iodine deficiency may produce no obvious symptoms, and TSH can remain normal even when iodine intake is low. More significant deficiency can eventually impair thyroid hormone production.

Can I take iodine if I have hypothyroidism?

Do not automatically start iodine supplements because you have hypothyroidism. Hypothyroidism has many causes, including autoimmune thyroid disease, and excess iodine can sometimes worsen thyroid dysfunction. Discuss supplementation with your doctor first.

Is iodised salt safe?

For most people, iodised salt is a safe and effective way to obtain iodine when used in appropriate amounts. However, iodised salt is still salt, so increasing salt intake solely to obtain more iodine is not advisable.

How much iodine do adults need each day?

The recommended intake for most adults is approximately 150 micrograms per day. Requirements increase during pregnancy and breastfeeding.

Can iodine deficiency cause a goitre?

Yes. When iodine intake is insufficient, increased TSH stimulation can cause the thyroid gland to enlarge as it attempts to capture more iodine and maintain thyroid hormone production.

The bottom line

Iodine deficiency is preventable in many cases, but correcting it does not mean taking large amounts of iodine. The thyroid needs the right amount — not simply more.

For most people, a balanced diet that includes reliable iodine sources and appropriately used iodised salt is enough. Vegetarians and vegans should pay particular attention to iodine because many plant foods naturally contain little iodine. Pregnant and breastfeeding women also have higher requirements and should discuss iodine supplementation with their healthcare provider.

If you suspect iodine deficiency, do not diagnose yourself based on symptoms alone. Thyroid blood tests, dietary assessment and, when appropriate, urinary iodine testing can help a healthcare professional determine what is actually going on.

Most importantly, avoid high-dose iodine supplements without medical advice. Both too little and too much iodine can interfere with thyroid function, so the goal should always be adequate iodine intake and healthy thyroid function.

To consult a Doctor at Sparsh Diagnostic Centre, call our helpline number 9830117733.

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Disclaimer:

No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

Sources and further reading

• Healthdirect: Iodine deficiency
• Healthdirect: Foods high in iodine
• World Health Organization: Iodine deficiency
• NIH Office of Dietary Supplements: Iodine fact sheet
• National Health Mission, India: National Iodine Deficiency Disorders Control Programme
• PMC: Biomarkers of Nutrition for Development — Iodine Review
• PMC: The role of micronutrients in thyroid dysfunction