What are the effects of iodine supplementation for preventing iodine deficiency disorders in children and adolescents?

Key messages

• Iodine supplementation improves thinking ability (cognitive function) slightly and may have little to no effect on growth (weight) in children and adolescents. None of the studies reported unwanted effects.

• Iodine supplementation likely reduces the occurrence of insufficient production of thyroid hormones (hypothyroidism), and risk of infant death (mortality) in places with high infant mortality rates. We are unsure about its effect on reducing enlargement of the thyroid gland (goitre).

• Future studies should focus on areas or populations in which lack of iodine could be a problem, and include children of lower socioeconomic levels. They should look at higher doses of iodine given during longer periods of treatment and follow-up times.

What is iodine, and why is it important?

Iodine is a mineral used to make thyroid hormones, which are required for the normal development of the body and brain. Given its role in human development, it is especially important that children receive enough iodine. Lack of iodine (iodine deficiency) in children can lead to delayed growth and development of the central nervous system, intellectual disability, infant death, and enlargement of the thyroid gland (goitre).

The primary sources of iodine in the diet are iodised salt, seafood, grains from iodine-rich soils, and dairy products. Iodine supplementation can be given as combined iodine and plant-based oil (iodised oil), which is injected into a muscle only once or yearly, or as potassium iodide tablets, capsules, or drops, given in a low dose daily or weekly.

What did we want to find out?

We wanted to know whether iodine supplementation results in fewer children and adolescents having iodine deficiency disorders compared with placebo (dummy treatment). We also wanted to know if receiving iodine supplementation was associated with any unwanted effects.

What did we do?

We searched for studies comparing iodine supplementation to placebo in children and adolescents at risk of iodine deficiency. We compared and summarised the results of the studies and rated our confidence in the evidence based on factors such as study methods and sizes.

What did we find?

We found eight studies (2528 people) that looked at the effects of preventive iodine supplementation in children and adolescents. The studies were conducted between 1982 and 2009 mainly in low‐income environs in Albania, Bangladesh, Colombia, Indonesia, Malawi, New Zealand, and Tanzania. The studies compared iodine supplementation by mouth (oral) (alone or with iron in one study) versus placebo.

Iodine supplementation versus placebo

• Iodine supplementation results in a slight increase in thinking ability (cognitive function) compared to placebo (1 study, 166 people).

• Iodine supplementation may result in little to no difference in children's weight compared to placebo (3 studies, 658 people).

• Iodine supplementation likely results in a large reduction in insufficient production of thyroid hormones (hypothyroidism) compared to placebo (1 study, 264 people).

• No study reported unwanted effects related to iodine or quality of life.

• Iodine supplementation likely reduces death due to any cause compared to placebo (1 study, 617 people).

• The evidence is very uncertain about the effect of iodine supplementation on the reduction of goitre (2 studies, 432 people). One study did not use robust methods. We removed it from our analyses and found that iodine likely results in a large reduction in goitre (1 study, 230 people).

Iodine plus iron supplementation versus placebo

• The evidence is very uncertain about the effect of iodine plus iron on weight (1 study, 146 people).

• No study reported cognitive function, hypothyroidism, unwanted effects, quality of life, death due to any cause, or goitre.

What are the limitations of the evidence?

Our confidence in the evidence ranged from high to very low. In cases where our confidence was limited, this was because:

• it is possible that people in the studies knew which treatment they were getting;

• the studies were done in different types of people;

• there are not enough studies to be certain about the results.

How up to date is this evidence?

The evidence is current to May 2025.