Comparative evaluation of green and black tea consumption on the iron status of omnivorous and vegetarian people

The effect of tea polyphenols on the bioavailability of iron and the iron status of man is controversially discussed. Especially women prior to menopause are a vulnerable group regarding their iron status, with a vegetarian diet increasing this risk. This study aimed to determine several iron status parameters for men and women consuming a mixed diet or being vegetarians and drinking tea. In a cross-over study, the effect of tea consumption on the iron status of healthy male and female omnivorous compared to vegetarian volunteers was tested. All volunteers consumed either green tea or black tea (each 1 L/d) for four weeks together with meals or avoided tea for four weeks (cross-over design). Blood samples were withdrawn prior to the one week depletion period, at the start of the intervention phase and thereafter weekly during intervention. The iron status parameters hemoglobin, hematocrit, transferrin, total iron and iron binding capacity were not affected by the consumption of tea. In contrast, plasma ferritin values were significantly reduced after tea consumption, especially in those women with basal ferritin values lower than 25 μg/L, already after two weeks of intervention with tea (1 L/d).

Research highlights
► Omnivorous group and vegetarian group did not differ in iron status parameters.
► Iron status was mostly unaffected by consumption of green or black tea (1 L/d).
► Daily consumption of green or black tea did not affect iron status in men.
► Tea consumption led to significantly reduced plasma ferritin values in some women.
► Women had higher vitamin C contents in plasma, enhancing non-heme iron absorption.