Supplements
iron deficiency worsens thyroid function
Part of: • Iron & ferritin
📅 Last reviewed: 2026-07-15 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: All trials, pooled (Meta-analysis)
How the studies fall
What the evidence shows
Iron deficiency impairs thyroid function (higher TSH, lower thyroid hormones, more thyroid autoimmunity) — iron is a cofactor for thyroid peroxidase (TPO).
The evidence (12)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Wei H et al 2026 · study_type: observational | observational | supports | low | Narrative review of Fe/Zn/Cu across thyroid diseases; states literature on iron-thyroid relationship is 'inconsistent' |
| Roeth E et al 2025 · study_type: observational | observational | mixed | low | 12-wk personalized supplementation, n=48: anti-TPO antibodies fell up to 22% in women alongside ferritin changes; multi-nutrient protocol, no isolated iron arm |
| Garofalo V, et al. 2023 · Nutrients | meta-analysis | supports | low | Iron deficiency associated with higher TSH, lower thyroid hormones, and thyroid autoimmunity (TPO is iron-dependent). |
| Suyama A et al 2026 · study_type: observational | observational | tested-null | low | Long-COVID cohort n=811: IGF-1 SD negatively correlated with ferritin (rho=-0.125,p<0.05) and TSH (rho=-0.202,p<0.01); FT4 positive with IGF-1 |
| eftekhari-2008 2008 | RCT | supports | moderate | Double-blind RCT (n=94 iron-deficient girls, 12wk ferrous sulfate vs placebo): iron repletion IMPROVED thyroid indices — TT4 +12%, TT3, T3RU up, rT3 -47% (all p<0.001 vs placebo). First interventional evidence iron->thyroid. |
| Abdo N et al 2026 · study_type: observational | observational | supports | moderate | Jordan cross-sectional n=3605: ID/IDA groups had lower FT3/FT4, higher TSH vs controls; hypothyroidism higher in IDA (p=0.0011) |
| Al-Fawaeir S et al 2025 · study_type: observational | observational | tested-null | low | Female hair-loss case-control n=200: hair-loss group had lower ferritin AND lower TSH/FT4 (concordant-low, not predicted inverse direction) |
| Vargas-Uricoechea, Urrego-Noguera, Vargas-Sierra, Pinzon-Fernandez 2024 · Int J Mol Sci | observational | contradicts | moderate | Ferritin NULL: median 73.5 ng/mL (IQR 32-125) in 524 AITD cases vs 76 (IQR 39-148) in 524 controls, p=0.278; low ferritin 20.6% vs 18.1%, p=0.31 (Table 2). 'No significant differences were found in relation to ferritin levels between cases and controls.' Every positive finding in this paper is ZINC, not iron. Authors attribute the null partly to excluding pregnant, lactating, anemic and abnormally-bleeding women. |
| Gierach 2024 · Endokrynol Pol | observational | supports | moderate | SR: iron/ferritin deficiency impairs heme-enzyme TPO activity and is associated with hypothyroidism |
| Al Khofi AS et al 2025 · study_type: observational | observational | supports | low | Saudi pregnancy cohort n=8542: low ferritin & low Hgb each associated with elevated TSH (p=0.001, p=0.034) |
| Sakhr HM et al 2026 · study_type: observational | observational | supports | low | Egyptian pediatric case-control n=150: thyroid-disorder children had lower ferritin + higher TSH; TPO Arg386His genotype linked to highest TSH |
| Mu SC et al 2026 · study_type: observational | observational | mixed | low | Taiwanese toddlers n=110: breastfeeding group had lower ferritin AND higher FT4 (opposite of predicted direction), thyroid all in normal range |
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