Iodine

Iodine is a trace mineral that the thyroid gland uses to make thyroid hormones. These hormones regulate metabolism and are essential for normal growth and brain development, particularly during pregnancy and infancy. Iodine is a nutrient of concern in vegan diets because the main sources in many countries are dairy products, fish and eggs.

Why iodine matters

Iodine deficiency can cause goitre (an enlarged thyroid) and hypothyroidism, with symptoms such as tiredness, weight gain and feeling cold. In pregnancy, deficiency can harm the developing baby’s brain; the World Health Organization regards iodine deficiency as a leading preventable cause of impaired cognitive development worldwide.

Recommended intakes

Iodine in plant foods

The iodine content of plant foods depends largely on how much iodine is in the soil where they are grown, which varies greatly by region. As a result, fruit, vegetables and grains are generally not reliable sources. Cow’s milk is a major source in countries such as the UK, partly because of iodine supplements in cattle feed and iodine-containing teat disinfectants, not because milk is naturally rich in it. Studies in the UK and elsewhere have found that vegans tend to have lower iodine intakes and status than people who eat animal products.

Vegan sources

• Iodised salt – many countries have salt iodisation programmes, which the WHO recommends as a public health measure. In the United States and many other countries, iodised table salt is widely available. In the UK, most salt sold is not iodised, so it must be specifically sought out. Sea salt, Himalayan salt and most salts used in processed foods are usually not iodised. Health bodies also advise limiting total salt intake, so iodised salt should replace rather than add to other salt.
• Fortified plant milks – a growing number of plant-based milks are fortified with iodine, often as potassium iodide. Fortification is not universal, so labels should be checked.
• Supplements – iodine is included in many vegan multivitamins, usually as potassium iodide.

Seaweed caution

Seaweed is sometimes recommended as a natural iodine source, but its iodine content varies enormously between species, batches and preparations.

• Kelp and kombu (brown seaweeds) can contain extremely high levels; a small serving may exceed the tolerable upper limit many times over.
• Nori, often used for sushi, typically contains much less.
• Seaweed may also contain contaminants such as arsenic, depending on the species.

Excessive iodine can cause thyroid problems, including both hypothyroidism and hyperthyroidism, especially in people with existing thyroid conditions. UK health bodies, including the British Dietetic Association, advise against relying on seaweed as an iodine source, particularly during pregnancy. Kelp supplements are not recommended as a reliable source because their iodine content is often unpredictable.

Upper limits

Practical guidance

Common approaches recommended for vegans include:

1. Use a modest amount of iodised salt in cooking, where available, as a replacement for non-iodised salt.
2. Choose plant milks fortified with iodine.
3. Consider a supplement providing around the recommended daily amount, particularly before and during pregnancy and while breastfeeding (see vegan pregnancy and children).
4. Avoid relying on kelp or other brown seaweeds.

People with thyroid conditions, or who take thyroid medication, should seek medical advice before changing their iodine intake.

This article is for general information. Individuals should consult a doctor or registered dietitian for personal advice.

See also

• Vitamin B12
• Vitamin D
• Meal planning
• How to Go Vegan