NutriStack
Grape Seed Extract and Iron, timing-sensitive.
Taken at the same time as an iron supplement, grape seed extract can bind iron in the digestive tract and reduce how much is absorbed. The effect is concentration-dependent: higher polyphenol loads block more iron. This matters most for people supplementing to correct or prevent iron deficiency (for example menstruating women, vegetarians, or those with diagnosed anemia), where reduced absorption can slow repletion. It is far less of a concern for those with adequate iron stores.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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At a glance
- Substances
- Grape Seed Extract and Iron
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Moderate
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Supplement
- Last verified
- May 30, 2026
Timing Sensitive · Moderate evidence
Timing Sensitive
What is happening. Taken at the same time as an iron supplement, grape seed extract can bind iron in the digestive tract and reduce how much is absorbed. The effect is concentration-dependent: higher polyphenol loads block more iron. This matters most for people supplementing to correct or prevent iron deficiency (for example menstruating women, vegetarians, or those with diagnosed anemia), where reduced absorption can slow repletion. It is far less of a concern for those with adequate iron stores.
Mechanism. Grape seed extract is rich in oligomeric proanthocyanidins and other polyphenols carrying catechol and galloyl groups. In the gut lumen these groups chelate dietary iron, forming insoluble, poorly absorbable iron-polyphenol complexes. Absorption and cell-culture studies show this lowers iron uptake in a dose-dependent way, an effect best established for non-heme iron and broadly consistent with the known inhibition of iron absorption by polyphenol-rich foods and beverages.
Recommendation. Separate grape seed extract and iron supplements by at least 2 hours. Take iron on an empty stomach or with vitamin C earlier in the day, and take grape seed extract with a different meal. If you are treating iron deficiency, prioritize the iron dose timing and keep polyphenol-rich supplements well away from it. Recheck ferritin and hemoglobin per your clinician if repletion seems slow.
Minimum separation. 2 hours
Sources (3)
- Human and Caco-2 cell absorption studies showing dietary polyphenols inhibit iron uptake in a dose-dependent manner.
- Studies on inhibition of non-heme iron absorption in humans by polyphenol-containing beverages.
- Pharmacology and nutrition reviews on polyphenol-iron chelation and non-heme iron bioavailability.
Stack Score
How this pair moves the number.
Effect on the composite score
If both Grape Seed Extract and Iron are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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