[Factors which modify the nutritional state of iron: tannin content of herbal teas]

Tannins are natural compounds that abound in herbs, wood and fruits. Their numerous hydroxyl radicals confer them a strong avidity for metals such as Fe, Zn and Cu. This property makes them strong inhibitors for the gastrointestinal absorption of these metals. Our purpose was to determine the tannin content of herbal infusions commonly consumed in Chile and other Latino American countries. The determination was performed from dessicated herbs with the Folin-Denis technique. Yerba mate, tea and oregano had the highest tannin content (117, 100 and 84 mg of tannic acid/g dry herb respectively). An intermediate level (between 20 and 40 of tannic acid/g) was for coca, matico, boldo, palto, laurel, orange and binojo. The lowest level of tannin for paico, cedrón, apio and manzanilla (< 10 mg/g). We conclude that the consumption of herbal teas at or around meals may inhibit the absorption of metals such as Fe, Zn, or Cu by decreasing their bioavailability.