Effects of green and black tea on iron uptake, storage, and availability for free radical reactions.
The interaction of iron with tea is important to health not only because tea polyphenols bind iron, but also because polyphenols may release iron from ferritin storage, resulting in free radical formation. In this study, we tested the effects of green and black teas on iron uptake and ferritin storage in Caco-2 cells, and on iron availability for free radical reactions in a cell-free system. Green and black teas (3 types each) were brewed at 1g/100ml for 5 minutes and tested for total phenol content. The two green and black teas most similar in total phenol content were used for subsequent experiments. Caco-2 cells were grown to confluence over 21 days and subsequently treated for 24 hours with 1, 2, or 4% green or black teas in the presence or absence of 100uM ferrous sulfate and ImM vitamin C. Green tea (at 2 and 4%) and black tea (at 4% only) reduced soluble intracellular iron content, apical iron content (at all levels except 1 % green), as well as intracellular ferritin (green at 2 and 4%, black at 4%) in Caco-2 cells (P < 0.05). Both black and green teas, at 15% strength, released iron from ferritin storage and induced significant (p < 0,0001) increases in hydroxyl radical formation in the presence of 110mg/ml ferritin. These data indicate that green and black teas reduce soluble intracellular and apical iron levels, and that they also reduce intracellular ferritin levels. Green tea was most effective at reducing intracellular iron levels. In addition, both teas are capable of releasing iron from ferritin storage and inducing free radical formation in the presence of ferritin.