23/05/2026
Do not take coffee or tea with meals!
Coffee and tea contain polyphenols that bind non-heme iron in the gut and form insoluble complexes that pass through unabsorbed.
Hurrell and colleagues (1999, Br J Nutr) tested this directly using radio-labeled iron in adult humans eating a standardized bread meal with different beverages. Absorption was quantified by erythrocyte incorporation of the tracer.
Compared to water, beverages containing 20 to 50 mg of polyphenols per serving reduced iron absorption by 50 to 70%. At 100 to 400 mg, the reduction was 60 to 90%. Black tea: 79 to 94%. Peppermint tea: 84%. Cocoa: 71%. Chamomile: 47%. Adding milk did not meaningfully change the effect.
The mechanism is specific to galloyl structure, not total phenolic content. Brune, Rossander, and Hallberg (1989, Eur J Clin Nutr) showed that tannic acid inhibits in a dose-dependent manner that tracks galloyl content: 5 mg cut absorption 20%, 25 mg cut it 67%, and 100 mg cut it 88%. Gallic acid inhibited equivalently per mol of galloyl groups. Catechin, which lacks that structure, showed no inhibition at all. Chlorogenic acid, the dominant polyphenol in coffee, inhibits but less potently than tannins.
Heme iron behaves differently. It's absorbed intact through the HCP1 transporter inside its porphyrin ring, shielded from polyphenol binding entirely. Non-heme iron from plants, eggs, and fortified foods is the vulnerable pool.
Vitamin C counteracts the interaction by reducing Feยณโบ to Feยฒโบ and forming a soluble ascorbate-iron complex that resists polyphenol binding. Hallberg and Hulthen (2000, Am J Clin Nutr) showed that adding 50 mg of vitamin C to a meal with significant inhibitors increased non-heme iron absorption 3 to 6-fold.
For anyone with borderline iron status, menstruation-related losses, a plant-based diet, or pregnancy, timing matters. A two-hour gap between the beverage and iron-rich foods, or pairing the meal with vitamin C, is the simplest fix.
Hurrell 1999. Brune 1989. The mechanism has been in the literature for three decades. It's rarely in standard dietary counseling, rarely on any bottle, and almost never mentioned by the industry selling iron.
Hurrell et al., Br J Nutr, 1999
Brune et al., Eur J Clin Nutr, 1989
Hallberg & Hulthen, Am J Clin Nutr, 2000
