Tea and Milk Don't Mix

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Addition of milk prevents vascular protective effects of tea

Lorenz1, Nicoline Jochmann1, Amélie von Krosigk1,

Martus2, Gert Baumann1, Karl Stangl1 and Verena Stangl1,*

1 Medizinische Klinik mit Schwerpunkt Kardiologie und Angiologie,

Charité—Universitätsmedizin Berlin, CCM, Charitéplatz 1, D-10117

Berlin, Germany

2 Institut für Biometrie und Klinische Epidemiologie, Charité—

Universitätsmedizin Berlin, CCM, Charitéplatz 1, D-10117 Berlin,

Germany

Received 13 September 2006; revised 28 November 2006; accepted 30

November 2006.

* Corresponding author. Tel: +49 30 450 513153; fax: +49 30 450

513932. E-mail address: verena.stangl@...

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.