The mechanism of the inhibition of iron absorption by tea.

Previous human studies have shown that drinking tea during meals significantly inhibits the absorption of both food iron and medicinal iron. This study provides evidence from experiments with rats that the tannins in the tea are responsible for the inhibition, probably by forming non-absorbable complexes with the iron within the intestinal lumen. The molar ratio of tannin: iron is dependent on the pH, being 1:1 at pH 2,0 2:1 at pH 5,5 and 3:1 at pH 8,0. Since tannins are present in many vegetable foods the formation of such complexes may be a factor in the poor availability for absorption of much food iron.