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Iron Absorption

Iron Absorption is the percentage of iron that is absorbed from a meal, also known as its bioavailability. Many supplements appear to interact with iron absorption in a meal, either in an additive or hindering fashion.

Research analysis lead by Kamal Patel
All content reviewed by Examine.com Team.
Last Updated:

Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what supplements affect iron absorption
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The mo re evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-c Green Tea Catechins Minor - See study
A decrease in iron absorption associated with green tea catechins has been noted
grade-c Zinc Minor Moderate See all 5 studies
Iron absorption is decreased when both iron and zinc exceed 10mg in a supplement given on an empty stomach. The inhibition does not appear to be relevant if the same ratio is at lower doses (500mcg) or if the minerals are ingested via food products.
grade-c Psyllium - Very High See 2 studies
No significant influence on iron absorption; it is possible the inhibitory effect of phytates in the small intestine are negated by the reduced pH in the colon that enhances mineral reuptake
grade-d Alpha-GPC Minor Moderate See 2 studies
It is possible that Alpha-GPC increases iron absorption from non-meat sources (nonheme iron), but the evidence is currently mixed and a very low dose of 46mg may be required (which would render supplementation irrelevant).
grade-d Curcumin  

All comparative evidence is now gathered in our ​A-to-Z Supplement Reference.

The evidence for each separate supplement is still freely available ​here.