Supplements
ferritin decreases 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 2024 · Int J Mol Sci | observational | contradicts | moderate | Population case-control: low ferritin associated with thyroid functional abnormalities and autoimmunity |
| 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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