Iodine for Cognitive Function
Adequate iodine during pregnancy protects a child's developing brain, and correcting maternal deficiency is one of the best-documented ways to prevent avoidable IQ loss. This evidence does not show that adults taking iodine supplements improve their own thinking or prevent dementia.
Why this grade7-layer evidence engine
The grade rests on a consistent, large body of observational and ecological research on maternal iodine status and offspring neurodevelopment. A Chinese meta-analysis of 37 studies (Qian, PMID 15734706) found children in iodine-deficient regions scored about 12.45 IQ points lower than those in sufficient regions, with roughly +8.7 points recoverable when supplementation began before or during pregnancy but only +1.5 points when it started in school age. A larger meta-analysis (Bougma, PMID 23609774; n=12,291) put the severe-deficiency deficit near 8 IQ points, and a systematic review (Skeaff, PMID 22254096) describes a 10-15 point penalty in severe deficiency.
Even mild maternal deficiency in otherwise iodine-replete countries matters. In the UK ALSPAC cohort (Bath, PMID 23706508; n=1,040), children of mildly deficient mothers had higher odds of bottom-quartile verbal IQ and reading (OR ~1.58). A Tasmanian cohort (Hynes, PMID 23633204) found literacy deficits of about 0.5 SD at age 9 that persisted even after the children themselves became iodine-replete, pointing to irreversible in-utero programming, so prevention must happen before and during pregnancy.
The grade is Moderate rather than higher because the Cochrane review of 14 trials (Harding, PMID 28260263; n=2,716) rated randomized cognitive-outcome data as low to very-low quality, even though the direction favored supplementation and trials in severely deficient areas are now considered unethical. Regulators and clinics back the developmental role: EFSA approves the claim that iodine contributes to normal cognitive function, NIH ODS and WHO stress its necessity for fetal brain development and endorse salt iodization, and Cleveland Clinic notes congenital hypothyroidism is a leading preventable cause of intellectual disability. Harvard and NHS add caution: aim for dietary or iodized-salt adequacy, since high-dose supplements can disturb thyroid function and offer no proven cognitive benefit in already-sufficient adults.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸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 = 0.748
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (1 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status