Iodine for Goiter

Verdict: Strong evidence: iodine prevents and reverses iodine-deficiency goiter

For goiter caused by iodine deficiency, adequate iodine intake is one of the best-proven interventions in all of nutrition: correcting deficiency shrinks the enlarged thyroid and prevents endemic goiter. This does not apply to goiter from autoimmune or nodular thyroid disease, where extra iodine offers no benefit and can be harmful.

S 🟢 S Strong Evidence Published

🔬Why this grade7-layer evidence engine

The Strong rating rests on an unusually deep and consistent evidence base for iodine-deficiency (endemic) goiter. A double-blind randomized trial in moderately deficient schoolchildren (PMID 16400058, n=310) showed that even a single oral iodine dose significantly reduced thyroid volume on ultrasound versus placebo, and a Cochrane review of iodine fortification (PMID 34528704) found moderate-certainty evidence that it lowers goiter prevalence and thyroid volume. Global surveillance and seminar reviews (PMIDs 18947032, 22378324, 18815969) document 70-90% drops in goiter where salt iodization reaches the population, with thyroid volume normalizing within 6-12 months.

Regulators and clinics are aligned. The WHO calls universal salt iodization a 'safe and effective strategy' for preventing iodine-deficiency disorders, and the FDA, EFSA, and NIH classify iodine as an essential nutrient required for thyroid-hormone production. This convergence of a population-level effect, a confirmatory RCT, and unanimous authority support is what pushes the grade to the top tier.

The crucial caveat is cause. In iodine-replete settings, most goiter stems from autoimmune (Hashimoto's) or nodular disease, not deficiency, and iodine will not regress these. The UK NHS warns that high-dose iodine over long periods 'could change the way your thyroid gland works,' and Harvard notes goiter can itself result from excess iodine. People with thyroid conditions should seek adequacy, not megadoses, and consult a clinician before supplementing.

⚖️

Scoring transparency

All scores computed by a 7-layer evidence engine — fully auditable

Raw score 0.80

← counter-evidence / ineffectiveeffective / strong evidence →

Final grade

S · Published

Confidence

74%

Broadly consistent

Evidence level

Cochrane high-quality SR/MA

How strongly each layer supports this effect

lower = less supportive

L1 ExamineGlobal benchmark

0.50

L3 MechanismPlausibility

0.75

L2 PubMedPrimary literature

0.85

L5 Clinical bodiesAuthoritative stance

0.85

L11 AI re-checkIndependent read

0.95

Against Mixed Supports

▸View the full decision path (audit trail)

compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.8
tier_from_score — 依分數區間映射至 tier letter
apply_hec_rules — 無高階證據可裁決
tier_strict_requirement_check — A 級條件達標
detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
decide_status — 依 tier + dispute 結果決定 status

📄PubMed studies (7)L2 · primary research & systematic reviews

Iodine deficiency in 2007: global progress since 2003

PMID: 18947032 2008 Other

Finding: Between 2003 and 2007 the number of iodine-deficient countries fell from 54 to 47 and the number with adequate iodine intake rose from 67 to 91. Household coverage of iodized salt reached approximately 70% globally, with corresponding sharp declines in school-age goiter prevalence in formerly endemic regions; authors (Andersson, de Benoist, Rogers) document USI as the single most successful population micronutrient intervention.

🟢 High quality Government Effect size: Number of iodine-sufficient countries: 67 (2003) -> 91 (2007); ~70% global household iodized salt coverage

View on PubMed

Iodine deficiency

PMID: 18815969 2008 Other

Finding: Comprehensive review concludes that salt iodization reduces goiter prevalence by 70-90% in formerly endemic areas within 1-5 years and effectively eliminates endemic cretinism; thyroid volume in schoolchildren decreases within 6-12 months of adequate intake. Iodized oil and iodized salt programs produce comparable goiter regression in remote populations. Authors describe iodine supplementation as 'one of the simplest and most cost-effective public health measures'.

🟢 High quality Academic Effect size: 70-90% reduction in goiter prevalence post-USI; thyroid volume normalization within 6-12 months

View on PubMed

Global iodine status in 2011 and trends over the past decade

PMID: 22378324 2012 Cross-sectional

Finding: Andersson et al. report that the number of iodine-deficient countries fell from 54 (2003) to 32 (2011) and iodine-sufficient countries rose to 105; goiter prevalence in school-age children dropped substantially in nearly every WHO region tracked, with the largest gains in Africa and South-East Asia. Confirms USI as the dominant driver of endemic goiter elimination over the past two decades.

🟢 High quality Government Effect size: Iodine-deficient countries 54 (2003) -> 32 (2011); ~30% of remaining global population still at risk

View on PubMed

Symposium on 'Geographical and geological influences on nutrition': Iodine deficiency disorders in the iodine-replete environment

PMID: 23472655 2013 Other

Finding: Zimmermann reviews controlled studies in mild-to-moderate deficiency: school-age children given iodine show measurable thyroid volume reduction and goiter regression within months; meta-analytic data place mean IQ gain at ~13 points in formerly severely deficient populations after iodine repletion. Endemic goiter is essentially abolished where USI achieves adequate coverage.

🟢 High quality Academic Effect size: Thyroid volume reduction documented within months; IQ gain ~13 points (severe deficiency repletion)

View on PubMed

Iodine supplementation improves cognition in iodine-deficient schoolchildren in Albania: a randomized, controlled, double-blind study

PMID: 16400058 2006 RCT (double-blind) n = 310

Finding: Zimmermann et al.: at 24 weeks the iodine group showed significantly higher median UIC, significantly reduced thyroid volume (i.e. goiter regression on ultrasound), and improved cognitive performance compared to placebo. Demonstrates that even a single oral iodine dose produces objective regression of goiter in moderately deficient children.

🟢 High quality Academic Effect size: Significant thyroid volume reduction vs placebo; UIC normalization

View on PubMed

Iodine fortification of foods and condiments, other than salt, for preventing iodine deficiency disorders

PMID: 34528704 2021 Cochrane SR

Finding: Cochrane review of 12 controlled studies (mostly schoolchildren in iodine-deficient regions) finds moderate-certainty evidence that non-salt iodine fortification reduces goiter prevalence and thyroid volume and increases UIC versus non-fortified comparator; effects directionally consistent with the much larger USI evidence base. Authors note salt iodization remains the gold-standard population strategy.

🟢 High quality Academic Effect size: Significant reductions in goiter prevalence and thyroid volume (moderate-certainty)

View on PubMed

Iodine deficiency in industrialized countries

PMID: 19460960 2009 Other

Finding: Re-emergence of mild iodine deficiency in several industrialized countries (UK, Australia, parts of Europe) is paralleled by rising goiter rates among schoolchildren and pregnant women; reintroduction or strengthening of mandatory salt iodization reverses these trends, recapitulating the historical USI evidence at a smaller scale.

🟢 High quality Academic Effect size: Reintroduction of USI reverses goiter trends in industrialized settings

View on PubMed

🏛️Regulatory & authoritative positionsL4/L5 · FDA / EMA / NIH ODS / Cochrane / Mayo …

L4a US FDA

Supportive

Iodized salt or iodized table salt is the article of commerce, salt for human food use, to which has been added cuprous iodide or potassium iodide. The label shall bear the statement 'This salt supplies iodide, a necessary nutrient'. Cuprous iodide and potassium iodide may be added to table salt as a source of dietary iodine in an amount not greater than 0.01 percent. source↗

L4b EU EFSA

Supportive

Iodine contributes to normal cognitive function, normal functioning of the nervous system, the maintenance of normal skin, normal production of thyroid hormones and normal thyroid function, and contributes to normal growth of children source↗

L4c UK NHS

Cautious

Adults need 140 micrograms (μg) of iodine a day. Most people should be able to get all the iodine they need by eating a varied and balanced diet. Taking high doses of iodine for long periods of time could change the way your thyroid gland works. This can lead to a wide range of different symptoms, such as weight gain. Taking 0.5mg or less a day of iodine supplements is unlikely to cause any harm. source↗

L4d TW TFDA / 衛福部

Supportive

孕婦碘的每日建議攝取量為225微克，較一般成人140微克高出許多；衛生福利部建議孕婦及哺乳婦使用加碘鹽，並可適量攝取含碘量豐富的食物，如海帶、海藻類等。 source↗

L4e WHO

Supportive

All food-grade salt, used in household and food processing should be fortified with iodine as a safe and effective strategy for the prevention and control of iodine deficiency disorders in populations living in stable and emergency settings. source↗

L5a NIH Office of Dietary Supplements

Supportive

Iodine is a mineral found in some foods. The body needs iodine to make thyroid hormones. These hormones control the body's metabolism and many other important functions. The body also needs thyroid hormones for proper bone and brain development during pregnancy and infancy. source↗

L5b Mayo Clinic

Supportive

L5c Cleveland Clinic

Supportive

L5d Harvard Health

Supportive

Goiter, a lump in the front of the neck from an enlarged inflamed thyroid gland, can result from hypothyroidism, hyperthyroidism, or an excessive iodine intake. source↗

L5e Specialty Society (condition-mapped)

Supportive

✓PMID 100% verifiedevery citation checked via NCBI Entrez

🔬7 PubMed studiesindependently re-checked by multiple sub-agents

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