Mineral Deficiencies
Impaired Iron Absorption
Polyphenols in coffee can bind nonheme iron and inhibit its intestinal absorption. 204 Drinking 150–250 ml of coffee with a test meal has been found to inhibit the absorption of iron by 24–73%. 205 , 206 , 207 , 208 Discontinuing coffee consumption significantly improved the response to iron supplements in Guatemalan toddlers. 209 To maximize iron absorption from a meal or iron supplements, concomitant intake of coffee should be avoided.
Impaired Zinc Absorption
Dietary inhibitors of zinc absorption, particularly phytate, increase the risk of zinc deficiency. 210 Zinc chelating compounds have been identified in coffee, 211 and coffee has been found to inhibit the bioavailability of zinc in vitro by 21–32%. 212 The effect of coffee consumption on human zinc status has not been well studied. Although there is one report that coffee appeared to inhibit zinc absorption in human volunteers, 213 discontinuation of coffee for 5 months did not affect plasma zinc levels in Guatemalan toddlers. 209