Addition of Milk Prevents Vascular Protective Effects of Tea by Lorenz M, Jochmann N, von Krosigk A, Martus P, Baumann G, Stangl K, Stangl V.
AIMS: Experimental and clinical studies indicate that tea exerts
protection against cardiovascular diseases. However, a question of
much debate is whether addition of milk modifies the biological
activities of tea. We studied the vascular effects of tea, with or
without milk, in humans and elucidated the impact of individual
milk proteins in cell culture experiments, with isolated rat aortic
rings and by HPLC analysis. METHODS AND RESULTS: A total of 16
healthy female volunteers consumed either 500 mL of freshly brewed
black tea, black tea with 10% skimmed milk, or boiled water as
control. Flow-mediated dilation (FMD) was measured by
high-resolution vascular ultrasound before and 2 h after
consumption. Black tea significantly improved FMD in humans
compared with water, whereas addition of milk completely blunted
the effects of tea. To support these findings, similar experiments
were performed in isolated rat aortic rings and endothelial cells.
Tea induced vasorelaxation in rat aortic rings and increased the
activity of endothelial nitric oxide synthase by phosphorylation of
the enzyme in endothelial cells. All effects were completely
inhibited by the addition of milk to tea. Of the various kinds of
milk proteins, the caseins accounted for these inhibiting effects
of milk, probably by formation of complexes with tea catechins.
CONCLUSION: Milk counteracts the favourable health effects of tea
on vascular function. This finding indicates the need for
particular awareness in the interpretation and design of studies
comprising nutritional flavonoids.
Medizinische Klinik mit Schwerpunkt Kardiologie und Angiologie,
Charité-Universitätsmedizin Berlin, CCM,
Charitéplatz 1, D-10117 Berlin, Germany.
PMID: 17213230 [PubMed - indexed for MEDLINE]
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