NutriStack
Calcium and Iron, a conflict.
Calcium significantly inhibits both heme and non-heme iron absorption when taken simultaneously.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
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What the row says.
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At a glance
- Pair type
- Conflict
- Evidence (highest tier)
- Strong
- Source citations
- 3 sources
- Stack Score effect
- −10 to your Stack Score (per scored conflict row).
- Scope
- Supplement × Supplement
- Last verified
- May 30, 2026
Conflict · Strong evidence
Conflict
What is happening. Calcium significantly inhibits both heme and non-heme iron absorption when taken simultaneously.
Mechanism. Calcium noncompetitively inhibits DMT1 and reduces ferroportin trafficking at the basolateral membrane. Calcium is NOT transported by DMT1. Reduces iron uptake by up to 50-60%.
Recommendation. Separate iron and calcium by at least 2 hours. Take iron in the morning on an empty stomach, calcium with a different meal.
Minimum separation. 120
Sources (3)
- Hallberg L et al. Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. Am J Clin Nutr. 1991 PMID 1831564
- Liu C, Kuang X, Li K, Guo X, Deng Q, Li D. Effects of combined calcium and vitamin D supplementation on osteoporosis in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials. Food & Function. 2020. PMID 33237064
- Yao P, Bennett D, Mafham M et al.. Vitamin D and Calcium for the Prevention of Fracture: A Systematic Review and Meta-analysis. JAMA Network Open. 2019. PMID 31860103
Stack Score
How this pair moves the number.
Effect on the composite score
If both Calcium and Iron are in the same stack, this pair applies −10 to your Stack Score (per scored conflict row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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