Zinc and iron compete for absorption
High doses of zinc can interfere with iron absorption, and vice versa. Both use the same transport mechanisms.
Take zinc and iron supplements at different times.
Separate by at least 2 hours
Zinc and iron compete for absorption. Take zinc and iron supplements at different times.
Separate by at least 2 hours
This interaction is rated “Caution” by Formulate. High doses of zinc can interfere with iron absorption, and vice versa. Both use the same transport mechanisms.
Studies from our registry that mention iron or zinc. Each links to the primary source and the other Formulate pages citing it.
Mentions zinc · 2017
Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage
Hemilä H · JRSM Open
Meta-analysis of 7 RCTs (n=575) found zinc lozenges (≥75mg/day elemental zinc) shortened cold duration by ~33%, with no significant difference between acetate and gluconate forms.
Mentions iron · 2017
Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women
Stoffel NU, Cercamondi CI, Brittenham G, et al. · Blood
Landmark absorption study showing iron supplements taken daily (or twice-daily) trigger hepcidin elevation that blocks subsequent absorption — supporting alternate-day dosing as more efficient for iron repletion.
Mentions zinc · 2013
Oral zinc for the common cold (Cochrane Review)
Singh M, Das RR · Cochrane Database of Systematic Reviews
Cochrane review of 18 RCTs found zinc reduced common cold duration and severity in healthy adults when taken within 24 hours of symptom onset, though adverse effects (taste disturbance, nausea) were common.
Mentions iron · 2010
Iron bioavailability and dietary reference values
Hurrell R, Egli I · American Journal of Clinical Nutrition
Reviews enhancers (vitamin C, meat) and inhibitors (phytate, polyphenols, calcium) of non-heme iron absorption, providing the mechanistic basis for pairing iron with vitamin C and separating it from tea/coffee.
Mentions zinc · 2005
Zinc-induced copper deficiency: a report of three cases initially recognized on bone marrow examination
Willis et al. · American Journal of Clinical Nutrition
Documented cases of copper deficiency from chronic high-dose zinc supplementation — supports the 1–2 mg copper pairing guideline.
Mentions iron · 2000
Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability
Hallberg and Hulthén · American Journal of Clinical Nutrition
Foundational model for non-heme iron absorption factoring vitamin C, phytates, tannins, and calcium interactions.
Guide
Zinc Supplement Guide 2026: Evidence-Based & Ranked
Learn which zinc forms actually shorten colds, how dosing affects testosterone and copper balance, and who faces the highest deficiency risk.
Guide
Iron Supplements Guide 2026: Evidence-Based & Ranked
Learn who needs iron supplements, what bloodwork to get, and which forms won’t wreck your stomach. Covers dosing science most doctors skip.
Guide
Zinc for Immune Support: Timing and Form Matter More Than Dose
Zinc genuinely shortens colds, but only when taken correctly. Lozenges within 24 hours of first symptoms — not pills, not after you're already sick.
Other interactions to know
Zinc depletes copper over time
Calcium significantly reduces iron absorption
Iron reduces levothyroxine absorption
Fluoroquinolones and tetracyclines chelate iron
Calcium may reduce zinc absorption
Antacids significantly reduce iron absorption
PPIs reduce non-heme iron absorption
Phytates in fiber reduce non-heme iron absorption
Check your full stack in the free interaction checker.
The free checker lets you add any combination of supplements and medications at once. The free web app goes further — every stack change surfaces interaction alerts automatically.
Medical disclaimer. This page is for educational purposes only and does not replace advice from a qualified healthcare provider.
Last medically reviewed: