Iodine: benefits, what it is for and who needs it

Iodine is an essential mineral because your body needs it to make thyroid hormones — thyroxine (T4) and tri-iodothyronine (T3) — which regulate metabolism, growth and development. The best-documented benefits of iodine concern normal thyroid function and the prevention of deficiency, especially in pregnancy and childhood. What the evidence does not show is that extra iodine helps anyone who already has adequate levels.

Below: what iodine does in the body, who is at greater risk of a shortfall, the reference intakes, what studies say about excess, and how to read a supplement label.

What does iodine do in the body?

Iodine is the raw material for thyroid hormones. The thyroid takes iodide from the blood through a specific transporter (the sodium-iodide symporter) and incorporates it into tyrosine residues to form T4 and T3. These hormones act as a timing signal for cells: they influence energy expenditure, body temperature, heart rate and the working of the nervous system.

When iodine is lacking, the thyroid cannot produce enough hormones and enlarges to try to capture more iodide from the blood — that enlargement is goitre. This is why, in regions with iodine-poor soils, goitre was common before salt iodisation.

Thyroid hormones are also essential for brain development, particularly during pregnancy and the first years of life. Severe iodine deficiency in pregnancy can impair a child's brain development, with effects on cognitive and motor function, hearing and speech.

What the evidence shows — and what it still does not

Iodine's role in preventing deficiency is well established. Severe iodine deficiency in pregnancy is considered the leading preventable cause of neurodevelopmental impairment worldwide, with clear effects on obstetric outcomes and on a child's intelligence quotient.

For mild to moderate deficiency, the picture is less clear. Early research suggests that even a mild to moderate shortfall in pregnancy may be associated with subtle changes in cognition and school performance, but the randomised trials that would confirm this relationship are still missing. In other words: we know that correcting a deficiency matters; we do not yet know whether supplementing people who already have adequate levels brings any additional benefit.

Some popular claims go far beyond what science supports. There is no solid evidence that iodine 'cures' disease, 'boosts' immunity or treats autoimmune conditions. And if your thyroid works normally, taking extra iodine does not speed up metabolism or burn fat.

Who is at greater risk of iodine deficiency?

The groups at greatest risk of insufficient intake are:

• Pregnant and breastfeeding women — their needs are higher than other adults'.
• People on restrictive diets without iodine sources such as fish, shellfish, dairy or iodised salt.
• People living in regions with iodine-poor soils and no salt iodisation programmes.
• People with intestinal absorption problems, who may absorb less iodine from food.

For most adults eating a varied diet with iodised salt, fish and dairy, deficiency is unlikely. If you have symptoms such as unexplained tiredness, dry skin, constipation or weight gain with no obvious cause, speak to a doctor and ask for a thyroid assessment. Hypothyroidism has many causes and iodine deficiency is only one of them — do not self-diagnose or start taking iodine on your own.

How much iodine do you need a day?

The most-cited reference intakes are 150 µg per day for adolescents and adults, rising to 250 µg per day in pregnancy and breastfeeding. A review specific to pregnancy and lactation gives values of 220 to 250 µg per day in pregnancy and 250 to 290 µg per day during breastfeeding. The two sources do not contradict each other: the first gives a single reference value, the second presents ranges depending on the review considered.

For regulatory context, the EU reference intake for iodine is 150 µg per day, and the value of 600 µg per day is the tolerable upper intake level set for adults.

These values are intake references, not instructions for taking supplements. For the dose question in detail, there is a separate page on iodine dosage.

Iodine for adults — and from what age it matters

Adults need iodine throughout life, not only in the years when they are planning a family. The reference intake of 150 µg per day applies from adolescence into adulthood, which is the practical answer to 'from what age': the adult reference value starts at adolescence, and children have lower reference values.

Who is the recommended intake actually for? It is a population reference, meant to cover the needs of nearly everyone in a healthy group. It is not a personal prescription. If your diet is varied and includes iodised salt, fish or dairy, you are probably already there. If it does not — a vegan diet without iodised salt, for instance — that is when the question becomes concrete.

Age also changes the risk side of the equation. The likelihood of thyroid disease rises as you get older, so an adult over 60 who is thinking about iodine should have a thyroid assessment first rather than start a supplement on a guess. Iodine supplements should never be given to a child without a healthcare professional's advice — at that age, excess can be more problematic than a shortfall.

Too much iodine is also a risk

The thyroid has protective mechanisms that let it cope with variations in iodine intake, but those mechanisms have limits. An acute iodine load can cause thyroid dysfunction — hypothyroidism or hyperthyroidism — in susceptible people, through failure of the so-called Wolff-Chaikoff effect or through the Jod-Basedow phenomenon.

In people with autoimmune thyroid disease, high doses of iodine can worsen thyroid function, so supplementation should not be started on your own without knowing whether there is a real need.

If you take medication or have a thyroid condition, the interactions page covers that ground in more detail.

Iodine in pregnancy and breastfeeding

Pregnancy is the period when iodine need is most critical. Severe deficiency is associated with adverse obstetric outcomes and a lower intelligence quotient in the child, and pregnant and breastfeeding women have higher needs than other adults.

During breastfeeding, iodine passes into breast milk and infants depend on it for normal physical and neurological growth; iodine concentrations in human milk vary widely between populations and over the course of lactation.

If you are pregnant, breastfeeding or planning a pregnancy, speak to a healthcare professional before taking any supplement — including iodine.

What a supplement label tells you

Iodine appears in various supplements, often combined with vitamins. In the TuttiBear range, for example, Appetite Control Gummies provide 100 µg of iodine per serving of 2 gummies (67% of the reference intake).

The numbers on a label are not the same as the numbers in research. One small randomised, double-blind, placebo-controlled trial in older adults, in a population with moderate iodine deficiency, used 80 µg of iodine per day for 3 months and reported a rise in urinary iodine concentration in the group that received iodine alone. That is a research dose in a specific group — it is not an instruction for you.

Note also that the same trial reported 42 µg and 28% in one of its arms, and 21 µg and 14% in another — figures that belong to the study design, not to any product. If you see numbers like these quoted online, check what they refer to before you act on them. And always check the label: dose per serving, number of gummies per container and warnings.

Gummies or tablets: what actually changes?

There are no studies directly comparing iodine gummies with iodine tablets, so we cannot say that one format is equivalent or superior to the other. What is known is that iodine is absorbed in the intestine and that the presentation form does not alter the mineral itself. Gummies have the practical advantage of being easy to chew, which may help people who have difficulty swallowing tablets. On the other hand, many gummies contain polyols, and excessive consumption may have a laxative effect — something to bear in mind if you are sensitive.

When to speak to a healthcare professional

Speak to a doctor or pharmacist before taking iodine if:

• You are pregnant, breastfeeding or planning a pregnancy.
• You have a diagnosed thyroid disease (hypothyroidism, hyperthyroidism, Hashimoto's thyroiditis, nodules or thyroid cancer).
• You take medication, especially anything that affects the thyroid.
• You have symptoms that worry you — tiredness, weight changes, dry skin, palpitations.
• You want to give a supplement to a child or adolescent: never do so without a healthcare professional's advice.

If you are unsure whether iodine could harm you, the safety page is the place to start.

Where the popular claims outrun the evidence

Search for iodine and you will find it credited with fixing tiredness, clearing skin, supporting weight loss and 'balancing hormones'. Almost none of that is established. The honest position is narrower: iodine prevents deficiency, and deficiency damages the thyroid and, in pregnancy, the developing brain. That is a real and important benefit. It is not the same as an energy boost.

The weight-loss claim deserves a direct answer. Correcting a deficiency may restore a metabolism that had slowed, but if your thyroid is already normal, extra iodine has nothing to correct. Research on iodine and body weight is at an early stage, and it has not shown that people with adequate intake lose weight by taking more.

Similarly, the idea that iodine 'detoxes' the body has no basis in the evidence we have. The body clears waste through the liver and kidneys; iodine is not involved in that process.

What to do next

If you eat fish, dairy or iodised salt regularly and you are not pregnant, you can probably stop reading — your intake is likely fine, and a supplement is unlikely to add anything. If you are pregnant, breastfeeding, vegan with a limited iodine intake, or living somewhere without iodised salt, that is when the question becomes worth asking properly, with a blood or urine test rather than a guess.

If you do decide to supplement, choose a product with a stated amount per serving and stay well within the reference intake unless a clinician tells you otherwise. Appetite Control Gummies are one option in the range for adults, at 100 µg per serving of 2 gummies, with the usual label warning that they contain polyols and should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Whatever you choose, read the label and check it against your own circumstances — and if you have any thyroid history at all, make that conversation happen before you buy, not after.