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Iodine for Hypothyroidism
Verdict: Published with Warning
Across 6 PubMed studies, the evidence for Iodine in Hypothyroidism grades Tier C — weak evidence. Effective, but with safety or population caveats.
C 🟠 C Weak Evidence Published with Warning
Why this grade7-layer evidence engine
Iodine is essential for thyroid hormone synthesis, but supplementing iodine in established hypothyroidism is not standard treatment. The Cochrane anchor (PMID 28260263) addresses pregnancy/preconception iodine supplementation, not hypothyroidism therapy.
Mayo Clinic L5b warns excess iodine can worsen hypothyroidism. Meta-analyses address deficiency/pregnancy populations, not clinical hypothyroidism management.
Tier C/PWW with scope warning is appropriate. Correct deficiency under medical supervision, but do not self-treat hypothyroidism with iodine supplements.
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Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditableRaw score 0.45
D
C
B
A
S
← counter-evidence / ineffectiveeffective / strong evidence →
Final grade
C · Published with Warning
Confidence
91%
Highly consistent evidence
Evidence level
E1
Cochrane high-quality SR/MA
▸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 = 0.448
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (1 positive vs 1 negative)，由 raw_score 決定
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 1 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status
PubMed studies (6)L2 · primary research & systematic reviews
Iodine supplementation for women during the preconception, pregnancy and postpartum period (Cochrane Review)
Finding: Across 14 trials (11 contributing data, >2700 women), iodine supplementation showed no clear effect on maternal hypothyroidism during pregnancy (RR 1.90, 95% CI 0.57-6.38) but reduced postpartum hyperthyroidism (RR 0.32, 95% CI 0.11-0.91) while increasing digestive intolerance (RR 15.33); authors concluded there were insufficient data to reach meaningful conclusions.
View on PubMed Effect of iodine supplementation in pregnant women on child neurodevelopment: a randomised, double-blind, placebo-controlled trial
Finding: In 832 mildly iodine-deficient pregnant women (median UIC 131 ug/L), 200 ug/day iodine had no effect on child IQ (verbal diff -0.7, 95% CI -2.9 to 1.5, p=0.77; performance diff -1.6, 95% CI -4.5 to 1.3, p=0.44) and did not improve maternal thyroid function (in fact free/total T4 fell slightly more in the iodine group, p<0.05).
View on PubMed Effect of excess iodine intake on thyroid diseases in different populations: A systematic review and meta-analyses including observational studies
Finding: Pooling observational studies (50 articles), adults with excess versus adequate iodine intake had roughly tripled odds of overt hypothyroidism (OR 2.78, 95% CI 1.47-5.27) and doubled odds of subclinical hypothyroidism (OR 2.03, 95% CI 1.58-2.62).
View on PubMed Association of Mild-to-Moderate Iodine Deficiency With Thyroid Function-A Systematic Review and Meta-analysis
Finding: Across 72 observational studies, mild-to-moderate iodine deficiency was NOT associated with altered thyroid function (e.g., in pregnant women TSH difference 0.03 mIU/L, 95% CI -0.05 to 0.12; fT4 -0.20 pmol/L, 95% CI -0.94 to 0.53), challenging the assumption that mild deficiency causes measurable thyroid dysfunction.
View on PubMed 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
Finding: Across 37 publications (10 RCTs, 4 non-RCT, 23 observational), iodine supplementation had no significant effect on child cognition (MD -0.18, 95% CI -1.22 to 0.87), language (MD 1.28, 95% CI -0.28 to 2.83) or motor scores (MD 0.28, 95% CI -1.10 to 1.66), and most studies showed no effect on maternal/infant TSH or free T4.
View on PubMed Effects of iodine supplementation on thyroid function parameter: Systematic review and meta-analysis
Finding: Across 11 studies (low/moderate risk of bias), 200 ug/day iodine reliably improved the surrogate marker urinary iodine concentration, but effects on maternal thyroid hormone concentrations were inconsistent (several studies showed no effect) and no pooled clinical thyroid-disease outcome was reported.
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
Cautious
It's best not to take iodine supplements unless your healthcare professional tells you to do so. Getting too much iodine from supplements could cause hypothyroidism or make it worse. It's rare to have low levels of iodine in the United States and many other developed countries. That's because iodine is added to foods such as salt. source↗
L5c Cleveland Clinic
Cautious
The main symptom of iodine deficiency is hypothyroidism. Hypothyroidism occurs when your body's iodine level decreases and your thyroid gland can't produce thyroid hormone. Your healthcare provider will treat your iodine deficiency with iodine supplements. Most adults should get 150 micrograms of iodine daily. In the U.S. and many other parts of the world, much of our food is already fortified … source↗
L5d Harvard Health
Cautious
In people with a genetic susceptibility, the onset of Hashimoto's thyroiditis can be triggered by factors such as high iodine intake, pregnancy, or cigarette smoking. source↗
L5e Specialty Society (condition-mapped)
Cautious
Infants, the elderly, pregnant and lactating women, and individuals with preexisting thyroid disease are susceptible to adverse effects of excess iodine intake. Many iodine, potassium iodide, and kelp supplements contain iodine in amounts that are up to several thousand times higher than the daily Tolerable Upper Limits. The ATA advises against the ingestion of iodine and kelp supplements conta… source↗