Vitamin C for Iron Absorption
Vitamin C clearly improves the absorption of non-heme (plant-based) iron from meals, but adding it to iron supplements does not meaningfully improve treatment outcomes in people who already have iron-deficiency anemia.
Why this grade7-layer evidence engine
The moderate (A) grade rests on a robust, well-understood mechanism. Classic single-meal radioisotope work by Lynch & Cook (PMID 6940487) and Hallberg (PMID 3700141) shows ascorbic acid reduces ferric iron to the more absorbable ferrous form and roughly doubles to triples non-heme iron uptake, reversing inhibition from tea, calcium, and phytate, with about 50 mg per meal as the practical threshold. Effects on heme iron are minimal.
Regulators and major clinics converge on this absorption effect: EFSA has authorized a cause-and-effect claim for non-heme iron absorption, and NIH ODS, Mayo Clinic, Cleveland Clinic, Harvard, and the American Society of Hematology all affirm pairing vitamin C with plant iron. The UK NHS is more cautious, urging diet over high-dose supplements.
The grade is held at moderate, not higher, because the mechanism does not translate into anemia treatment. An RCT (PMID 33136134, n=440) found iron plus vitamin C equivalent to iron alone, and meta-analyses (PMID 37739692, n=905; PMID 40765927, n=1930) found either no significant benefit or a statistically significant but clinically trivial hemoglobin gain (about 0.14 g/dL). High-dose vitamin C should also be avoided in hereditary hemochromatosis.
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 = 0.745
- 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 — 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