Iodine is essential for the body to make thyroid hormone. Low levels of iodine may cause an underactive thyroid gland and symptoms of hypothyroidism (eg, tiredness, constipation and weight gain). Iodine deficiency in pregnant women may cause problems for the baby, including learning disability. There has been a worldwide campaign to prevent iodine deficiency by using salt containing added iodine. However, iodine deficiency is still a widespread problem in many countries. Mild iodine deficiency may still affect some people in the UK.
What is iodine deficiency?
Iodine is needed to make thyroid hormone. The body does not make iodine so your body needs foods that contain iodine. If you do not have enough iodine in your body then you cannot make enough thyroid hormone.
Which foods contain iodine?
Iodine is present in soil and seawater. If the soil has a low level of iodine then the food crops grown in that soil will also have a low iodine level. The low iodine levels in the soil will also reduce the iodine levels in farm animals grazing in that area. Foods which tend to have a higher amount of iodine include dairy products, seafood, meat, some breads and eggs.
How common is iodine deficiency?
Underactive thyroid gland due to iodine deficiency from birth (congenital hypothyroidism) is the most common preventable cause of severe learning disability in the world. There has been a worldwide use of salt with added iodine (iodized salt) since the 1990s. Since then the number of countries in the world with iodine deficiency has fallen. However, there are still some countries, particularly in Africa and Asia, with widespread iodine deficiency. Mild iodine deficiency may still occur in some people in the UK.
Because there are still some countries with widespread iodine deficiency, the World Health Organization is continuing a campaign to end iodine deficiency throughout the world.
What are the symptoms of iodine deficiency?
Iodine deficiency can lead to swelling of the thyroid gland (goitre) and to an underactive thyroid gland (hypothyroidism). In hypothyroidism, there is a reduced level of thyroid hormone (thyroxine) in the body. This can cause various symptoms, the most common being tiredness, weight gain, constipation, aches, dry skin and feeling cold.
Iodine deficiency in women who are pregnant or breast-feeding can be very harmful for the baby. Severe iodine deficiency in the mother may cause miscarriage, stillbirth and premature delivery and may cause the baby to have abnormalities when they are born (congenital abnormalities).
Children of mothers with severe iodine deficiency during pregnancy may have learning difficulties and problems with growth, hearing and speech. Even mild iodine deficiency during pregnancy may be associated with lower intelligence in children.
What tests are needed to diagnose iodine deficiency?
Iodine deficiency can be diagnosed by measuring the amount of iodine in a urine sample. However, this is usually used to monitor iodine levels in whole communities rather than for individual people. A blood test for thyroid function will also be needed for anyone who is thought to have iodine deficiency.
What is the treatment for iodine deficiency?
The treatment for iodine deficiency is to take iodine supplements. However, taking too much iodine can cause the thyroid gland to become overactive (hyperthyroidism).
People who move from a country with low iodine levels to a country with adequate iodine levels may also develop thyroid problems. Their thyroid glands will have become very good at taking up and using small amounts of iodine. Moving to an area with higher iodine levels may then cause increased thyroid activity and may even cause an overactive thyroid (iodine-induced hyperthyroidism).
How can iodine deficiency be prevented?
Elimination of iodine deficiency has been a major goal of the World Health Organization. Salt with added iodine (Iodized salt) is usually used. Injections containing iodine are occasionally used in regions of the world where widespread use of iodized salt is not possible. Adding iodine to the water supply has also been effective in some regions.
Further reading and references
Iodine deficiency disorders; World Health Organization
Chung HR; Iodine and thyroid function. Ann Pediatr Endocrinol Metab. 2014 Mar19(1):8-12. doi: 10.6065/apem.2014.19.1.8. Epub 2014 Mar 31.
Kapil U; Health consequences of iodine deficiency. Sultan Qaboos Univ Med J. 2007 Dec7(3):267-72.
Taylor PN, Okosieme OE, Dayan CM, et al; Therapy of endocrine disease: Impact of iodine supplementation in mild-to-moderate iodine deficiency: systematic review and meta-analysis. Eur J Endocrinol. 2013 Oct 2170(1):R1-R15. doi: 10.1530/EJE-13-0651. Print 2014 Jan.
Eastman CJ, Zimmermann M; The Iodine Deficiency Disorders
Iodine; The British Dietetic Association, May 2013