Iodine deficiency
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Omar Elshafei, MD[2]
Overview
Iodine deficiency is a state of inadequate dietary iodine supply that limits the synthesis of the thyroid hormones thyroxine and triiodothyronine. Because iodine has no known biological function in humans other than as a constituent of thyroid hormone, every consequence of deficiency is mediated through impaired thyroid hormone production. The resulting spectrum of disease is collectively termed the iodine deficiency disorders and includes goiter, hypothyroidism, impaired fetal and childhood neurodevelopment, cretinism, reduced fertility, stillbirth and increased perinatal and infant mortality.
Iodine deficiency arises where soil and groundwater are iodine-poor, most classically in mountainous regions, heavily leached river basins and flood plains, and it therefore behaves as an environmental rather than a genetic disorder. Populations, not individuals, are the unit of assessment: there is no validated biomarker of long-term iodine status in a single person, and urinary iodine concentration is interpreted as a population median. Severe deficiency produces goiter and hypothyroidism and, when it occurs during gestation, irreversible neurological injury in the offspring. Mild-to-moderate deficiency is far more common worldwide, including in industrialised countries, and its clinical consequences are more subtle and more contested.
The mainstay of control is universal salt iodization, one of the most cost-effective public health interventions available, supplemented by iodine tablets or annual iodized oil in groups or regions that salt iodization does not reach. Where deficiency is confirmed, repletion reverses goiter in children and normalises thyroid function, but long-standing nodular goiter and established cretinism are not reversible. Rapid repletion of a chronically deficient population can transiently unmask thyroid dysfunction, so iodine programmes require ongoing monitoring for both deficiency and excess.
Historical Perspective
Endemic goiter and cretinism were described in antiquity and were recognised as geographically clustered long before iodine was identified as the causative nutrient. Systematic prophylaxis began in the early twentieth century, and salt iodization was first introduced in Switzerland and the United States in the 1920s, becoming the foundation of all subsequent control programmes.[1]
| Period | Development | Significance |
|---|---|---|
| Antiquity to 18th century | Description of endemic goiter and cretinism in mountainous and flood-plain populations | Established the geographic clustering that later pointed to an environmental cause[1] |
| 19th century | Recognition of iodine as an essential dietary constituent and of its relation to endemic goiter | Provided the rationale for iodine prophylaxis[1] |
| 1920s | Introduction of iodized salt in Switzerland and the United States | Salt iodization becomes the mainstay of prevention[1] |
| 1950s to 1980s | Iodized oil trials in severely deficient populations; delineation of neurological and myxedematous cretinism | Demonstrated that fetal brain damage is preventable and defined the two cretinism phenotypes[2] |
| 1994 | Randomised administration of iodine to children from birth to three years of age (n = 689) and to women at each trimester of pregnancy (n = 295) in severely deficient Xinjiang, China | Defined the timing of fetal brain vulnerability and showed that treatment after the second trimester confers little neurological benefit[3] |
| 1990 to 2007 | Global commitment to eliminate iodine deficiency disorders; WHO, UNICEF and ICCIDD publish standardised assessment and monitoring criteria in successive editions | Created the median urinary iodine concentration cut-offs and programme indicators still in use[4] |
| 2003 to 2020 | Number of countries with iodine deficiency falls from 54 to 32 and then to 21; countries with adequate intake rise from 67 to 118 | Documents one of the largest and least recognised public health gains of the modern era[5][6] |
| 2026 | American Thyroid Association publishes updated guidelines covering iodine nutrition in preconception, pregnancy and the postpartum period | Current reference standard for individual clinical management; emphasises the absence of any valid individual-level biomarker[7] |
Classification
Iodine deficiency is classified in two complementary ways: by the severity of deficiency in a population, defined epidemiologically by the median urinary iodine concentration, and clinically by the life stage at which deficiency occurs and the syndrome it produces.
Classification by Population Iodine Status
| Population group | Median urinary iodine concentration (µg/L) | Interpretation |
|---|---|---|
| School-age children and general population | <20 | Severe iodine deficiency[4][1] |
| School-age children and general population | 20 to 49 | Moderate iodine deficiency[4] |
| School-age children and general population | 50 to 99 | Mild iodine deficiency[4] |
| School-age children and general population | 100 to 199 | Adequate iodine nutrition[4] |
| School-age children and general population | 200 to 299 | More than adequate intake[4] |
| School-age children and general population | ≥300 | Excessive intake, with risk of iodine-induced thyroid dysfunction[4] |
| Non-pregnant, non-lactating women | 100 to 199 | Population iodine sufficiency[7] |
| Pregnant women | <150 | Insufficient iodine nutrition[4][7] |
| Pregnant women | 150 to 249 | Optimal iodine nutrition[7] |
| Pregnant women | ≥500 | Excessive intake[4] |
| Lactating women | >100 | Threshold suggested by the World Health Organization for adequate nutrition, although urinary iodine alone may not fully reflect status in this group because iodine is excreted in both urine and breast milk[7] |
Classification by Life Stage and Clinical Syndrome
| Life stage | Principal manifestations |
|---|---|
| Fetus | Miscarriage, stillbirth, congenital anomalies, increased perinatal mortality, neurological and myxedematous cretinism, psychomotor impairment[2][8] |
| Neonate | Neonatal goiter, neonatal hypothyroidism, elevated screening TSH, increased infant mortality[1][7] |
| Child and adolescent | Goiter, subclinical or overt hypothyroidism, impaired cognitive and motor function, impaired somatic growth[1][9] |
| Adult | Diffuse goiter progressing to multinodular goiter with functional autonomy, hypothyroidism, iodine-induced hyperthyroidism following repletion, impaired fertility[10] |
| All ages | Increased susceptibility of the thyroid to radioactive iodine following nuclear accidents[1] |
Pathophysiology
Under normal conditions the human body contains approximately 15 to 20 mg of iodine, of which over 70% is held within the thyroid gland.[7] Circulating iodide is concentrated by the sodium-iodide symporter at the basolateral membrane of the thyroid follicular cell, organified onto tyrosyl residues of thyroglobulin, and coupled to form thyroxine and triiodothyronine.
When habitual intake falls below requirement, intrathyroidal iodine stores are depleted and a series of adaptive responses is triggered: expression of the sodium-iodide symporter increases, thyroidal iodide clearance rises, and hormone synthesis shifts preferentially toward the less iodine-costly triiodothyronine. These adaptations are driven and maintained by an increase in TSH, which also produces follicular hyperplasia and hypertrophy. Goiter is therefore best understood as the visible cost of successful adaptation rather than as a failure of it.[2][10]
Over years, the diffusely enlarged gland becomes nodular, and clones of follicular cells acquire growth and functional autonomy. This is the substrate for two apparently opposite phenomena: hypothyroidism when adaptation is finally overwhelmed by severe deficiency, and iodine-induced hyperthyroidism when an autonomous nodular gland is suddenly exposed to an iodine load, whether from a fortification programme, an iodinated contrast agent or amiodarone.[10][11]
In pregnancy the iodine requirement rises because maternal thyroid hormone production increases, renal iodine clearance increases, and iodine is transferred across the placenta to the fetus, which does not synthesise its own thyroid hormone until approximately the twelfth gestational week and remains partly dependent on maternal thyroxine thereafter. The sodium-iodide symporter mediates placental iodide transfer, so maternal deficiency translates directly into fetal deficiency.[7][8]
An important qualification applies to milder states. Because the only known function of iodine is thyroid hormonal, any consequence of deficiency must be mediated through altered hormone production, yet systematic review of observational data shows that mild-to-moderate deficiency is not consistently accompanied by measurable alterations in TSH or free thyroxine across most population groups. The mechanistic link between mild deficiency and adverse outcomes therefore remains incompletely explained.[12]
| Habitual dietary iodine intake below requirement | |||||||||||||||||||||||||||
| Depletion of intrathyroidal iodine stores and preferential triiodothyronine synthesis | |||||||||||||||||||||||||||
| Rise in TSH with increased sodium-iodide symporter expression and iodide trapping | |||||||||||||||||||||||||||
| Follicular hyperplasia and hypertrophy | |||||||||||||||||||||||||||
| Diffuse goiter progressing to multinodular goiter with functional autonomy and risk of iodine-induced hyperthyroidism | Inadequate thyroxine supply causing hypothyroidism and, in gestation, impaired fetal neurodevelopment | ||||||||||||||||||||||||||
Causes
| Category | Examples |
|---|---|
| Environmental | Iodine-poor soil and groundwater in mountainous regions, glaciated terrain, heavily leached river basins and flood plains; reliance on locally produced food from such areas[1] |
| Dietary | Absence or low household coverage of iodized salt; avoidance of dairy products, eggs, fish and other marine foods; use of non-iodized speciality salts such as sea salt or rock salt; exclusively plant-based diets[7][13] |
| Goitrogens | Cyanogenic glycosides from inadequately processed cassava, millet and cruciferous vegetables; thiocyanate from tobacco smoking; perchlorate and nitrate, which compete with iodide at the sodium-iodide symporter[1] |
| Coexisting micronutrient deficiency | Selenium, iron and vitamin A deficiency, each of which impairs thyroid hormone metabolism and blunts the response to iodine repletion[1] |
| Increased physiological requirement | Pregnancy and lactation, in which increased hormone production, increased renal iodine clearance and fetal or infant transfer raise the daily requirement[7] |
| Iatrogenic and other | Long-term parenteral nutrition without iodine supplementation; highly restrictive therapeutic or elimination diets[1] |
Differentiating Iodine deficiency from other Diseases
Iodine deficiency must be distinguished from other causes of goiter and hypothyroidism. The single most useful discriminator in an iodine-replete setting is thyroid peroxidase antibody status, since autoimmune thyroid disease rather than iodine deficiency is the dominant cause of hypothyroidism where iodine intake is adequate.[10]
| Disease | Distinguishing clinical features | Thyroid function pattern | Antibodies | Iodine status and other findings |
|---|---|---|---|---|
| Iodine deficiency | Endemic distribution; diffuse goiter in children and young people, becoming nodular with age; dietary or geographic risk factors | Normal to elevated TSH; free thyroxine low only in severe deficiency | Negative | Low population median urinary iodine concentration; elevated thyroglobulin; increased radioiodine uptake[1][10] |
| Hashimoto's thyroiditis | Sporadic; firm irregular gland or atrophic thyroid; frequently other autoimmune disease | Elevated TSH with normal or low free thyroxine | Thyroid peroxidase antibody positive in the majority | Normal iodine status; heterogeneous hypoechoic pattern on ultrasound[7] |
| Graves' disease | Diffuse goiter with bruit, ophthalmopathy, pretibial myxedema | Suppressed TSH with elevated free thyroxine or triiodothyronine | Thyrotropin receptor antibody positive | Diffusely increased radioiodine uptake[7] |
| Iodine-induced thyroid dysfunction | Recent iodine load from amiodarone, iodinated contrast, antiseptics, seaweed or a new fortification programme | Either suppressed TSH with thyrotoxicosis in an autonomous nodular gland, or elevated TSH from failure to escape the acute Wolff-Chaikoff effect | Variable | High urinary iodine concentration; low radioiodine uptake in iodine excess[10][11] |
| Congenital dyshormonogenesis and Pendred syndrome | Goiter presenting in infancy or childhood; sensorineural hearing loss in Pendred syndrome | Elevated TSH with normal or low free thyroxine | Negative | Normal iodine status; abnormal perchlorate discharge test; family history[1] |
| Drug-induced goiter or hypothyroidism | Exposure to lithium, amiodarone, antithyroid drugs, tyrosine kinase inhibitors or interferon | Elevated TSH, occasionally suppressed | Usually negative | Normal iodine status unless the drug is iodine-containing; resolution on withdrawal[7] |
| Goitrogen ingestion | Heavy reliance on inadequately processed cassava or millet; tobacco smoking | Normal to elevated TSH | Negative | Frequently coexists with true iodine deficiency and aggravates it[1] |
| Thyroid nodule or thyroid cancer | Solitary or dominant nodule, rapid growth, fixation, cervical lymphadenopathy, hoarseness | Usually normal | Negative | Suspicious sonographic features requiring fine needle aspiration[7] |
| Subacute thyroiditis | Painful tender gland after a viral prodrome | Transient thyrotoxicosis followed by hypothyroidism then recovery | Negative | Raised inflammatory markers; near-absent radioiodine uptake[7] |
| Central hypothyroidism | Features of other pituitary hormone deficiency; no goiter | Low or inappropriately normal TSH with low free thyroxine | Negative | Normal iodine status; pituitary imaging abnormal[7] |
Epidemiology and Demographics
Iodine deficiency remains one of the most widespread nutritional disorders worldwide, although its prevalence has fallen substantially. In 2003, iodine deficiency was a public health problem in 54 countries, and 36.5% of school-age children, corresponding to 285 million children, were estimated to have insufficient iodine intake.[14] By 2011 the number of iodine-deficient countries had fallen from 54 to 32 and the number with adequate intake had risen from 67 to 105, although 29.8% (95% CI 29.4, 30.1) of school-age children, or 241 million, still had insufficient intakes.[5]
By 2020, 124 countries had legislation for mandatory salt iodization and 21 had legislation permitting voluntary iodization, and 88% of the global population was using iodized salt. Urinary iodine surveys had been performed in 152 of 194 countries over the preceding 15 years and were nationally representative in 132. The number of countries with adequate iodine intake had nearly doubled from 67 in 2003 to 118 in 2020, while 21 countries remained deficient and 13 had excessive intakes attributable either to high groundwater iodine or to over-iodized salt.[6]
The most recent global scorecard, based on national median urinary iodine concentration in school-age children obtained from epidemiological studies conducted between 2009 and 2023 across 194 World Health Organization Member States, classifies countries as follows.[15]
| Data source | Insufficient (median UIC <100 µg/L) | Adequate (median UIC 100 to 299 µg/L) | Excessive (median UIC ≥300 µg/L) |
|---|---|---|---|
| National data | 21 countries | 91 countries | 8 countries |
| Sub-national data | 2 countries | 11 countries | 2 countries |
| No recent data | 59 countries | ||
Using a different denominator, in 2023 there were 18 countries with insufficient dietary iodine intake among the 127 countries with nationally representative data available, corresponding to approximately one-third of the world's population.[7]
Deficiency is not confined to low-income settings. Approximately half of Europe has remained mildly iodine deficient, and intakes in several industrialised countries have declined.[1] In the United States, National Health and Nutrition Examination Survey data show that a substantial proportion of pregnant women are iodine insufficient, with median urinary iodine concentration as a population biomarker declining since the early 2000s.[7]
Pregnant and lactating women, infants and young children are the groups at greatest risk at any given level of population intake, because their requirements are highest relative to intake.[16]
Risk Factors
| Risk factor | Comment |
|---|---|
| Residence in a region of known iodine insufficiency | Residing in an area of severe iodine insufficiency while not using iodine-containing supplements or iodized salt is an explicit indication for TSH testing at presentation of pregnancy and every four to six weeks up to mid-pregnancy[7] |
| Pregnancy and lactation | Requirement rises to 250 µg daily; the first trimester is the period of greatest fetal vulnerability[7][17] |
| Non-use of iodized salt | Includes deliberate substitution with sea salt or rock salt, and salt restriction for hypertension without an alternative iodine source[7][13] |
| Avoidance of dairy products and seafood | Vegan and dairy-free diets remove the principal iodine sources in many national food supplies[7] |
| Malabsorption | Impairs iodine assimilation and is listed as an indication for supplementation in women planning pregnancy[7] |
| Infancy and early childhood | Weaning infants not receiving iodine-containing complementary foods are at particular risk even where school-age children are replete[8] |
| Coexisting selenium, iron or vitamin A deficiency | Blunts thyroid hormone synthesis and the response to iodine repletion[1] |
| Goitrogen exposure | Inadequately processed cassava or millet, tobacco smoking, and environmental perchlorate or thiocyanate[1] |
Screening
There is no recommended programme for screening asymptomatic individuals for iodine deficiency, and this is a deliberate methodological position rather than an omission. There are no validated biomarkers with which to assess chronic iodine intake at the individual level; currently available biomarkers, including urinary iodine concentration, are intended to be interpreted only as medians in populations.[7] This limitation is quantitative as well as conceptual: ten repeat collections, whether spot samples or 24-hour samples, are required to estimate an individual woman's iodine status reliably.[18]
Screening in iodine deficiency is therefore population surveillance, undertaken with standardised indicators.
| Indicator | Target population | Criterion for sufficiency | Limitations |
|---|---|---|---|
| Median urinary iodine concentration | School-age children; pregnant women | 100 to 199 µg/L in school-age children; 150 to 249 µg/L in pregnancy | Reflects recent intake only; valid as a group median, not for individuals[4][7][18] |
| Serum or whole-blood thyroglobulin | School-age children; pregnant women | Responds to both deficient and excess intake | No consensus threshold values in pregnancy and poor harmonisation between assays[7] |
| Neonatal TSH | Newborns in regions with congenital hypothyroidism screening | Prevalence of neonatal TSH greater than 5.0 mU/L should be less than 3% | Affected by timing relative to the neonatal TSH surge and by iodophor antiseptic use at delivery[7] |
| Breast milk iodine concentration | Lactating women | Median of 100 to 200 µg/L suggested as adequate | Reflects recent intake; substantial intra-individual variability; no formal minimum threshold established[7] |
| Total goiter rate | School-age children | Less than 5% | Slow to respond to programme change; observer-dependent when assessed by palpation[4] |
| Household iodized salt coverage | General population | Programme indicator of intervention reach | Measures delivery rather than physiological status[6] |
Serum thyroid function tests are not sensitive indicators of population iodine status in most groups, including pregnant and postpartum women, because of substantial variation between individuals in the capacity of the thyroid to adapt to insufficient iodine, even in severely deficient regions.[7] Consistent with recommendations for the general population, there is insufficient evidence to support universal thyroid function screening in women planning pregnancy, in pregnant women or postpartum; testing is instead directed by risk factors, of which residence in a severely iodine-insufficient area is one.[7]
Natural History, Complications and Prognosis
Natural History
Deficiency is initially compensated, and a diffuse goiter may be the only manifestation for years. With continued deficiency the gland becomes nodular and develops functional autonomy, so that the epidemiology of thyroid disease in a chronically deficient population shifts from goiter in the young toward toxic nodular disease in the elderly.[10] When deficiency is severe, adaptation fails and overt hypothyroidism supervenes; when it occurs during gestation, the consequences fall on the fetus and are largely irreversible.
Complications
| Severity of deficiency | Established complications | Strength of evidence |
|---|---|---|
| Severe | Adverse obstetrical outcomes, maternal and neonatal hypothyroidism, perinatal and infant mortality, low child intelligence quotient and child neurocognitive impairment | Strong[7] |
| Severe, gestational | Neurological cretinism with intellectual disability, deaf-mutism, strabismus and spasticity with a thyroid that is usually present; myxedematous cretinism with profound hypothyroidism, short stature and an atrophic thyroid | Strong[2][1] |
| Mild to moderate, obstetric outcomes | Not associated with adverse obstetric outcomes | Consistent across studies[7] |
| Mild to moderate, child neurodevelopment | Observational data show associations with impaired fetal brain development; children of women deficient before 14 weeks of gestation had lower intelligence quotient scores in a dose-dependent manner | Observational only; adequately powered randomised trials have not been performed[7][17] |
| Childhood | Impaired cognitive and motor function and reduced somatic growth, both of which improve with repletion | Randomised trial evidence[19][20][9] |
| Following population repletion | Transient increase in the incidence of hyperthyroidism, predominantly in young people, and a sustained increase in the incidence of hypothyroidism in young and middle-aged subjects | Prospective population data[11][21] |
The observational evidence linking milder gestational deficiency to child outcomes is substantial. In an individual participant data meta-analysis of 6180 mother and child pairs from three European cohorts, maternal iodine status showed a positive curvilinear association with mean verbal intelligence quotient, and the association was strongest before 12 weeks of gestation, weaker between 12 and 14 weeks, and no longer present after 14 weeks.[17] In a first-trimester analysis of 1040 women in the Avon Longitudinal Study of Parents and Children, inadequate maternal iodine status was associated with poorer child cognitive outcomes at eight years.[22] In the Tasmanian Gestational Iodine Cohort, children of mothers with gestational urinary iodine concentration below 150 µg/L had poorer educational outcomes at nine years, and these reductions persisted into adolescence at 15-year follow-up despite the children growing up in an iodine-replete environment.[23][24]
Prognosis
Prognosis depends almost entirely on the life stage at which deficiency occurs and on how early it is corrected. Repletion in childhood reverses goiter and improves cognitive and motor function.[19][20] Long-standing multinodular goiter with established autonomy does not regress and may become thyrotoxic on repletion.[10] Neurological cretinism is irreversible once established: iodine given before conception prevents it, whereas treatment begun after the second trimester or after delivery confers little neurological benefit.[3]
Diagnosis
History and Symptoms | Physical Examination | Laboratory Findings | Electrocardiogram | X Ray | CT | MRI | Echocardiography or Ultrasound | Other Imaging Findings | Other Diagnostic Studies
History and Symptoms
The clinical presentation of iodine deficiency is that of hypothyroidism and its sequelae, together with the local effects of thyroid enlargement.[7] Many affected individuals are asymptomatic and present only with a visible or palpable goiter. Symptomatic patients may report fatigue, cold intolerance, weight gain, constipation, dry skin, menstrual disturbance or subfertility. A large or retrosternal goiter may cause neck discomfort, dysphagia, dyspnea or positional stridor.
The history should establish geographic origin and residence, use of iodized salt at home and in prepared foods, intake of dairy products, eggs and marine foods, adherence to vegan or elimination diets, use of prenatal or other supplements containing iodine, exposure to goitrogens including cassava and tobacco smoking, recent exposure to iodinated contrast media or amiodarone, and, in women, pregnancy status and pregnancy planning.[7][1]
Physical Examination
Examination centres on the thyroid. The World Health Organization grading system classifies goiter as grade 0 when the thyroid is neither palpable nor visible, grade 1 when it is palpable but not visible with the neck in the neutral position, and grade 2 when it is visible with the neck in the neutral position.[4] Diffuse symmetrical enlargement is typical in children and young adults, whereas nodularity and asymmetry predominate in older adults with long-standing deficiency. Signs of hypothyroidism such as bradycardia, delayed relaxation of the deep tendon reflexes, dry skin and periorbital edema indicate severe deficiency. In children, growth and developmental assessment should be documented.
Laboratory Findings
| Test | Expected finding | Interpretive caution |
|---|---|---|
| Serum TSH | Normal in mild deficiency; elevated in moderate to severe deficiency | Best single marker of thyroid status but an insensitive marker of iodine status in most groups[7][12] |
| Serum free thyroxine | Normal until deficiency is severe | Assay-dependent, and the pregnancy-specific reference interval differs from the non-pregnant interval[7] |
| Serum thyroglobulin | Elevated, falling with repletion | Bidirectional marker that also rises with iodine excess; no consensus threshold in pregnancy and poor assay harmonisation[7] |
| Thyroid peroxidase antibody | Negative in pure iodine deficiency | Positive result redirects the diagnosis toward autoimmune thyroid disease[7] |
| Spot urinary iodine concentration | Low group median | Not interpretable in an individual; ten repeat collections are required for an individual estimate[18][7] |
| Neonatal TSH on newborn screening | Prevalence of values above 5.0 mU/L rises above 3% | Confounded by timing relative to the neonatal surge and by iodophor antiseptic use[7] |
Electrocardiogram
There is no electrocardiogram abnormality specific to iodine deficiency. Because the clinical presentation of deficiency is that of hypothyroidism and its sequelae, findings such as sinus bradycardia, low QRS voltage and prolonged QT interval may be encountered when deficiency has produced overt hypothyroidism, and they resolve with restoration of euthyroidism.[7]
Imaging and Other Diagnostic Studies
Thyroid ultrasound is the imaging modality of choice and permits measurement of thyroid volume, which is used as a population indicator and to monitor the response to repletion, and characterisation of nodules. Chest x ray, computed tomography and magnetic resonance imaging have no role in the diagnosis of iodine deficiency itself and are reserved for assessing retrosternal extension and tracheal compression in large goiters; iodinated contrast should be avoided where possible in a nodular gland because of the risk of precipitating hyperthyroidism. Radioiodine uptake is characteristically increased in iodine deficiency and is markedly reduced in iodine excess, which can help resolve an ambiguous presentation.[1][10] Fine needle aspiration is indicated for nodules with suspicious sonographic features rather than for the evaluation of deficiency.[7]
| Goiter, features of hypothyroidism, or dietary and geographic risk factors for iodine deficiency | |||||||||||||||||||||||||||
| Serum TSH and free thyroxine; thyroid peroxidase antibody; thyroid ultrasound if goiter is present | |||||||||||||||||||||||||||
| Antibody positive with heterogeneous hypoechoic gland: Hashimoto's thyroiditis or other autoimmune thyroid disease | Antibody negative with dietary or geographic risk: assess iodine intake, group median urinary iodine concentration and serum thyroglobulin | ||||||||||||||||||||||||||
| Optimise dietary iodine and supplement as indicated; treat overt hypothyroidism with levothyroxine; avoid abrupt large iodine loads in nodular goiter | |||||||||||||||||||||||||||
Treatment
Medical Therapy | Surgery | Primary Prevention | Secondary Prevention | Cost-Effectiveness of Therapy | Future or Investigational Therapies
Initial Management
Initial management establishes the severity and context of deficiency rather than treating a laboratory number. The clinician should determine whether overt hypothyroidism is present, whether the patient is pregnant, planning pregnancy or lactating, whether the goiter is diffuse or nodular, and whether there are compressive symptoms. Iodine intake is optimised ideally before conception rather than after it, since the fetal brain is most vulnerable in the first trimester.[7][17]
Two cautions apply at the outset. First, an abrupt large iodine load given to a chronically deficient patient with an autonomous nodular gland may precipitate hyperthyroidism; population data from a cautious fortification programme showed an increase in the incidence of hyperthyroidism predominantly in young people, and a sustained increase in the incidence of hypothyroidism in young and middle-aged subjects with previous moderate deficiency.[11][21] Second, excessive iodine exposure should be avoided in pregnancy except for defined medical indications such as saturated solution of potassium iodide or iodinated contrast media.[7]
Medical Therapy
| Setting | Recommended regimen | Strength and certainty |
|---|---|---|
| Pregnant and lactating women | Total daily iodine intake of 250 mcg, provided by dietary iodine complemented by supplements as required | Strong recommendation, moderate certainty[7] |
| Women at risk of deficiency by geographic region, dietary restriction or malabsorption | 150 mcg per day of supplemental iodine, ideally started at least 3 months before planned pregnancy and continued until lactation is complete | Conditional recommendation, moderate certainty[7] |
| Low-resource countries or regions of severe deficiency where neither salt iodization nor daily supplements are feasible | An annual dose of 400 mg iodized oil to women of childbearing age and pregnant women | Conditional recommendation, moderate certainty; not intended as a long-term strategy where other options exist[7] |
| Pregnant women taking antithyroid drugs for Graves' disease or levothyroxine for hypothyroidism | Apply the same iodine supplementation recommendations as for other pregnant women | Conditional recommendation, low certainty[7] |
| All pregnant women | Avoid sustained dietary intake and supplement use exceeding 500 mcg daily | Strong recommendation, moderate certainty[7] |
| Deficient children and adolescents | Repletion through iodized salt or supplementation | Randomised trials show improvement in cognitive performance following repletion[19][20] |
| Overt hypothyroidism from severe deficiency | Levothyroxine in addition to iodine repletion, titrated to a normal TSH | Standard management of overt hypothyroidism[7] |
Supplemental iodine doses reported in the literature for the assessment of obstetric and offspring outcomes have ranged from 50 to 300 mcg per day, in line with the range of region-specific background dietary intakes of the populations studied.[7]
The evidence base underlying these recommendations should be represented honestly on this page rather than flattened. In mildly iodine-deficient pregnant women, daily iodine supplementation had no effect on child neurodevelopment at ages 5 to 6 years in a randomised, double-blind, placebo-controlled trial.[25] A systematic review of 37 publications comprising 10 randomised controlled trials, 4 non-randomised interventions and 23 observational studies found that most studies showed no effect of supplementation on maternal or infant TSH or free thyroxine, although most randomised trials showed a reduction in maternal thyroglobulin and three showed prevention or diminution of the gestational rise in thyroid volume; meta-analysis of two randomised trials showed no effect on child cognitive scores (mean difference -0.18; 95% CI -1.22, 0.87), language scores (mean difference 1.28; 95% CI -0.28, 2.83) or motor scores (mean difference 0.28; 95% CI -1.10, 1.66).[26] An earlier systematic review of 9 randomised controlled trials and 8 observational studies found that gestational supplementation reduced maternal thyroid volume and serum thyroglobulin, and pooled analysis of two randomised trials measuring cognitive function in school-age children showed modest benefits on perceptual reasoning (standardised mean difference 0.55; 95% CI 0.05, 1.04; P = 0.03) and on the global cognitive index (standardised mean difference 0.27; 95% CI 0.10, 0.44; P = 0.002), with significant heterogeneity between studies.[27] A Cochrane review of 14 trials conducted in 13 countries found that supplementation may reduce postpartum hypothyroidism and perinatal mortality, with low certainty.[28]
Current guidance therefore rests on biological extrapolation from severe deficiency rather than on demonstrated neurodevelopmental benefit in mild-to-moderate deficiency, a limitation that the guideline itself makes explicit.[7]
Procedural / Surgical Therapy
There is no procedural or surgical treatment for uncomplicated iodine deficiency, and repletion is the definitive therapy. Intervention is directed at the structural and functional consequences of long-standing deficiency.
| Indication | Procedure | Comment |
|---|---|---|
| Compressive or retrosternal goiter with dysphagia, dyspnea or stridor | Thyroidectomy | Long-standing nodular goiter does not regress with iodine repletion[10] |
| Suspicion of thyroid cancer on fine needle aspiration | Thyroidectomy | Managed according to oncological principles[7] |
| Toxic multinodular goiter or iodine-induced hyperthyroidism in an autonomous gland | Radioactive iodine therapy or thyroidectomy | Anticipated when a chronically deficient nodular gland is repleted[11][10] |
| Graves' disease in pregnancy requiring surgery | Preoperative saturated solution of potassium iodide | One of the defined exceptions to the avoidance of excess iodine in pregnancy[7] |
Long-Term Management
Long-term control is a public health rather than an individual undertaking. Universal salt iodization is the mainstay, and its durability is demonstrated by the fact that 88% of the global population uses iodized salt and that the number of countries with adequate iodine intake nearly doubled from 67 in 2003 to 118 in 2020.[6] Programmes require periodic surveys of median urinary iodine concentration with standardised methodology, monitoring of household salt coverage, and surveillance for excess as well as deficiency, since 13 countries had excessive intakes in 2020 attributable either to high groundwater iodine or to over-iodized salt.[6]
At the individual level, patients repleted for deficiency should have thyroid function reassessed after repletion, and those with nodular goiter monitored for the development of thyrotoxicosis. Discontinuation of an effective programme leads to recurrence, so sustainability rather than short-term correction is the therapeutic goal.[1] Annual iodized oil should not be used as a long-term strategy or in regions where other options for adequate iodine nutrition are available.[7]
Special Populations
| Population | Management considerations |
|---|---|
| Women planning pregnancy | 150 mcg per day of supplemental iodine, ideally begun at least 3 months before conception, since the association between maternal iodine status and child verbal intelligence quotient is strongest before 12 weeks of gestation and absent after 14 weeks[7][17] |
| Pregnant women | Total intake of 250 mcg daily; ceiling of 500 mcg daily; supplementation advised for women in general during this life stage rather than only for those in at-risk areas, although strategies vary by geographic region[7] |
| Lactating women and their infants | Continue 250 mcg daily; direct infant supplementation and maternal supplementation have both been studied in randomised comparison, and the optimal metric for assessing population iodine status during lactation remains unclear[7][29] |
| Weaning infants and young children | At risk even where school-age children in the same population are replete; iodine-containing complementary foods are required[8] |
| Patients on vegan, dairy-free or seafood-free diets, or not using iodized salt | Higher supplemental amounts may be needed, guided by regional population iodine status and individual dietary pattern[7] |
| Patients with multinodular goiter and functional autonomy | Repletion may precipitate hyperthyroidism; monitor thyroid function after any increase in iodine intake and avoid unnecessary iodinated contrast media and amiodarone[11][7] |
| Populations undergoing new salt iodization | Anticipate a transient rise in hyperthyroidism incidence and a sustained rise in hypothyroidism incidence in those with previous moderate deficiency; these risks are small relative to the benefits of correcting deficiency[21][1] |
| Low-resource settings without salt iodization or supplement access | An annual dose of 400 mg iodized oil to women of childbearing age and pregnant women, as an interim measure only[7] |
Case Studies
References
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 Zimmermann MB (2009). "Iodine deficiency". Endocrine Reviews. 30 (4): 376–408. doi:10.1210/er.2009-0011. PMID 19460960.
- ↑ 2.0 2.1 2.2 2.3 Delange F (1994). "The disorders induced by iodine deficiency". Thyroid. 4 (1): 107–28. doi:10.1089/thy.1994.4.107. PMID 8054857.
- ↑ 3.0 3.1 Cao XY, Jiang XM, Dou ZH, Rakeman MA, Zhang ML, O'Donnell K, Ma T, Amette K, DeLong N, DeLong GR (1994). "Timing of vulnerability of the brain to iodine deficiency in endemic cretinism". The New England Journal of Medicine. 331 (26): 1739–44. doi:10.1056/NEJM199412293312603. PMID 7984194.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 "Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, 3rd edition". World Health Organization, UNICEF and ICCIDD. 2007. Retrieved 2026-08-12.
- ↑ 5.0 5.1 Andersson M, Karumbunathan V, Zimmermann MB (2012). "Global iodine status in 2011 and trends over the past decade". The Journal of Nutrition. 142 (4): 744–50. doi:10.3945/jn.111.149393. PMID 22378324.
- ↑ 6.0 6.1 6.2 6.3 6.4 Zimmermann MB, Andersson M (2021). "GLOBAL ENDOCRINOLOGY: Global perspectives in endocrinology: coverage of iodized salt programs and iodine status in 2020". European Journal of Endocrinology. 185 (1): R13–R21. doi:10.1530/EJE-21-0171. PMID 33989173 Check
|pmid=value (help). - ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 7.24 7.25 7.26 7.27 7.28 7.29 7.30 7.31 7.32 7.33 7.34 7.35 7.36 7.37 7.38 7.39 7.40 7.41 7.42 7.43 7.44 7.45 7.46 7.47 7.48 7.49 7.50 7.51 7.52 7.53 7.54 7.55 7.56 7.57 7.58 7.59 7.60 7.61 Korevaar T, Leung AM, Alexander EK, Bliddal S, Boelaert K, Brenta G, Chou R, Dhillon-Smith R, Dosiou C, Eaton JL, Guan H, Kilpatrick SJ, Lasserre BJ, Lee SY, Maraka S, Meister KD, Morris-Wiseman LF, Nguyen CT, Pearce EN, Shan Z (2026). "American Thyroid Association 2026 Guidelines for Thyroid Disease in Preconception, Pregnancy, and Postpartum". Thyroid. 36 (5): 481–544. doi:10.1177/10507256261445624. PMID 42219800 Check
|pmid=value (help). Vancouver style error: initials (help) - ↑ 8.0 8.1 8.2 8.3 Zimmermann MB (2012). "The effects of iodine deficiency in pregnancy and infancy". Paediatric and Perinatal Epidemiology. 26 (Suppl 1): 108–17. doi:10.1111/j.1365-3016.2012.01275.x. PMID 22742605.
- ↑ 9.0 9.1 Zimmermann MB (2011). "The role of iodine in human growth and development". Seminars in Cell & Developmental Biology. 22 (6): 645–52. doi:10.1016/j.semcdb.2011.07.009. PMID 21802524.
- ↑ 10.00 10.01 10.02 10.03 10.04 10.05 10.06 10.07 10.08 10.09 10.10 Zimmermann MB, Boelaert K (2015). "Iodine deficiency and thyroid disorders". The Lancet. Diabetes & Endocrinology. 3 (4): 286–95. doi:10.1016/S2213-8587(14)70225-6. PMID 25591468.
- ↑ 11.0 11.1 11.2 11.3 11.4 11.5 Bülow Pedersen I, Laurberg P, Knudsen N, Jørgensen T, Perrild H, Ovesen L, Rasmussen LB (2006). "Increase in incidence of hyperthyroidism predominantly occurs in young people after iodine fortification of salt in Denmark". The Journal of Clinical Endocrinology and Metabolism. 91 (10): 3830–4. doi:10.1210/jc.2006-0652. PMID 16849408.
- ↑ 12.0 12.1 Aarsland TE, Aakre I, Stea TH, Henjum S, Markhus MW, Strand TA, Dahl L, Korevaar T, Bakken KS, Sleire SN (2025). "Association of Mild-to-Moderate Iodine Deficiency With Thyroid Function: A Systematic Review and Meta-analysis". Advances in Nutrition. 16 (9): 100471. doi:10.1016/j.advnut.2025.100471. PMID 40633808 Check
|pmid=value (help). Vancouver style error: initials (help) - ↑ 13.0 13.1 "Iodine: Fact Sheet for Health Professionals". Office of Dietary Supplements, National Institutes of Health. Retrieved 2026-08-12.
- ↑ Andersson M, Takkouche B, Egli I, Allen HE, de Benoist B (2005). "Current global iodine status and progress over the last decade towards the elimination of iodine deficiency". Bulletin of the World Health Organization. 83 (7): 518–25. PMID 16175826.
- ↑ "Global scorecard of iodine nutrition 2025". Iodine Global Network. 2025. Retrieved 2026-08-12.
- ↑ Pearce EN, Andersson M, Zimmermann MB (2013). "Global iodine nutrition: where do we stand in 2013?". Thyroid. 23 (5): 523–8. doi:10.1089/thy.2013.0128. PMID 23472655.
- ↑ 17.0 17.1 17.2 17.3 17.4 Levie D, Korevaar T, Bath SC, Murcia M, Dineva M, Llop S, Espada M, van Herwaarden AE, de Rijke YB, Ibarluzea JM, Sunyer J, Tiemeier H, Rayman MP, Guxens M, Peeters RP (2019). "Association of maternal iodine status with child IQ: a meta-analysis of individual-participant data". The Journal of Clinical Endocrinology and Metabolism. 104 (12): 5957–5967. doi:10.1210/jc.2018-02559. PMID 30920622. Vancouver style error: initials (help)
- ↑ 18.0 18.1 18.2 König F, Andersson M, Hotz K, Aeberli I, Zimmermann MB (2011). "Ten repeat collections for urinary iodine from spot samples or 24-hour samples are needed to reliably estimate individual iodine status in women". The Journal of Nutrition. 141 (11): 2049–54. doi:10.3945/jn.111.144071. PMID 21918061.
- ↑ 19.0 19.1 19.2 Zimmermann MB, Connolly K, Bozo M, Bridson J, Rohner F, Grimci L (2006). "Iodine supplementation improves cognition in iodine-deficient schoolchildren in Albania: a randomized, controlled, double-blind study". The American Journal of Clinical Nutrition. 83 (1): 108–14. PMID 16400058.
- ↑ 20.0 20.1 20.2 Gordon RC, Rose MC, Skeaff SA, Gray AR, Morgan KM, Ruffman T (2009). "Iodine supplementation improves cognition in mildly iodine-deficient children". The American Journal of Clinical Nutrition. 90 (5): 1264–71. doi:10.3945/ajcn.2009.28145. PMID 19726593.
- ↑ 21.0 21.1 21.2 Petersen M, Knudsen N, Carlé A, Andersen S, Jørgensen T, Perrild H, Ovesen L, Rasmussen LB, Thuesen BH, Bülow Pedersen I (2019). "Increased Incidence Rate of Hypothyroidism After Iodine Fortification in Denmark: A 20-Year Prospective Population-Based Study". The Journal of Clinical Endocrinology and Metabolism. 104 (5): 1833–1840. doi:10.1210/jc.2018-01993. PMID 30551165.
- ↑ Bath SC, Steer CD, Golding J, Emmett P, Rayman MP (2013). "Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC)". Lancet. 382 (9889): 331–7. doi:10.1016/S0140-6736(13)60436-5. PMID 23706508.
- ↑ Hynes KL, Otahal P, Hay I, Burgess JR (2013). "Mild iodine deficiency during pregnancy is associated with reduced educational outcomes in the offspring: 9-year follow-up of the gestational iodine cohort". The Journal of Clinical Endocrinology and Metabolism. 98 (5): 1954–62. doi:10.1210/jc.2012-4249. PMID 23633204.
- ↑ Hynes KL, Otahal P, Burgess JR, Oddy WH, Hay I (2017). "Reduced Educational Outcomes Persist into Adolescence Following Mild Iodine Deficiency in Utero, Despite Adequacy in Childhood: 15-Year Follow-Up of the Gestational Iodine Cohort Investigating Auditory Processing Speed and Working Memory". Nutrients. 9 (12): 1354. doi:10.3390/nu9121354. PMID 29236073.
- ↑ Gowachirapant S, Jaiswal N, Melse-Boonstra A, Galetti V, Stinca S, Mackenzie I, Thomas S, Thomas T, Winichagoon P, Srinivasan K, Zimmermann MB (2017). "Effect of iodine supplementation in pregnant women on child neurodevelopment: a randomised, double-blind, placebo-controlled trial". The Lancet. Diabetes & Endocrinology. 5 (11): 853–863. doi:10.1016/S2213-8587(17)30332-7. PMID 29030199.
- ↑ Dineva M, Fishpool H, Rayman MP, Mendis J, Bath SC (2020). "Systematic review and meta-analysis of the effects of iodine supplementation on thyroid function and child neurodevelopment in mildly-to-moderately iodine-deficient pregnant women". The American Journal of Clinical Nutrition. 112 (2): 389–412. doi:10.1093/ajcn/nqaa071. PMID 32320029 Check
|pmid=value (help). - ↑ Taylor PN, Okosieme OE, Dayan CM, Lazarus JH (2014). "Therapy of endocrine disease: Impact of iodine supplementation in mild-to-moderate iodine deficiency: systematic review and meta-analysis". European Journal of Endocrinology. 170 (1): R1–R15. doi:10.1530/EJE-13-0651. PMID 24088547.
- ↑ Harding KB, Peña-Rosas JP, Webster AC, Yap CM, Payne BA, Ota E, De-Regil LM (2017). "Iodine supplementation for women during the preconception, pregnancy and postpartum period". The Cochrane Database of Systematic Reviews. 3: CD011761. doi:10.1002/14651858.CD011761.pub2. PMID 28260263.
- ↑ Bouhouch RR, Bouhouch S, Cherkaoui M, Aboussad A, Stinca S, Haldimann M, Andersson M, Zimmermann MB (2014). "Direct iodine supplementation of infants versus supplementation of their breastfeeding mothers: a double-blind, randomised, placebo-controlled trial". The Lancet. Diabetes & Endocrinology. 2 (3): 197–209. doi:10.1016/S2213-8587(13)70155-4. PMID 24622750.