European Heart Journal Advance Access originally published online on April 28, 2007
European Heart Journal 2007 28(10):1266-1267; doi:10.1093/eurheartj/ehm093
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Addition of milk prevents vascular protective effects of tea: reply
Medizinische Klinik mit Schwerpunkt Kardiologie und Angiologie
Charité—Universitätsmedizin Berlin, CCM
Charitéplatz 1
D-10117 Berlin
Germany
Medizinische Klinik mit Schwerpunkt Kardiologie und Angiologie
Charité—Universitätsmedizin Berlin, CCM
Charitéplatz 1
D-10117 Berlin
Germany
Medizinische Klinik mit Schwerpunkt Kardiologie und Angiologie
Charité—Universitätsmedizin Berlin, CCM
Charitéplatz 1
D-10117 Berlin
Germany
Tel: +49 30 450 513186 Fax: +49 30 450 513941 E-mail address: mario.lorenz{at}charite.de
Tel: +49 30 450 513075 Fax: +49 30 450 513932 E-mail address: karl.stangl{at}charite.de
Tel: +49 30 450 513153 Fax: +49 30 450 513932 E-mail address: verena.stangl{at}charite.de
We appreciate the interesting comments of Pfeuffer and Schrezenmeir regarding our paper. The authors state that the increase in flow-mediated dilation (FMD) after consumption of black tea in our study was just 3.5% above the control response. However, this value lies within the physiological range in the increase in FMD after consumption of beverages or food. Similar increases in FMD were observed after consumption of a high-flavanol cocoa drink as well as after oral ingestion of epicatechin,1 after consumption of dark chocolate,2 drinking of white and red wine,3 and consumption of black tea.4,5
We measured FMD after 2 h, according to maximal flavonoid bioavailability. Chronic tea consumption for 4 weeks improved FMD after volunteers had consumed the tea the evening before measurements.5
The authors further doubt whether complexes between catechins and casein, if formed at all in the intestinal tract, would remain once the caseins are broken down to amino acids and peptides. As we have shown in Table 2 of our paper, tea catechins become complexed as soon as milk is added to tea. Whether these complexes are broken down after digestion of the caseins and whether the catechins are subsequently released and absorbed later on represent interesting questions. We are also aware of the study by van het Hof et al.,6 who did not observe a difference in plasma catechin concentrations after consumption of black tea with or without milk. This objection needs to be further investigated. A plausible explanation of the fact that we observed an impairment of FMD response after addition of milk to tea may be that the catechins, owing to the longer retention period in the digestive tract, could have been modified and thus rendered physiologically inactive. The suggestion by the authors to measure the vasodilatory response at later time points is an important issue that should be addressed in future studies.
The remarks of the authors on the beneficial effects of milk products, including casein, on blood pressure are interesting. At no point, however, are we questioning these effects, nor did we intend to investigate the effects of milk alone on vasodilatory responses. We merely attempted to study the interaction of milk with tea and to determine whether milk could have an adverse affect on the well-known positive vasodilatory effects of tea.
All participants of our study fasted overnight and consumed only a croissant without filling, thus limiting the influence of fat or any surrounding food matrix on the FMD response.
We fully agree with the authors that, in vivo, the endothelial cells lining the blood vessels would not be exposed to caseins or other milk proteins. This part of the study was conducted as a supplementary line of evidence to the in vivo measurements of FMD as proof of principle. We especially attempted to identify the individual milk proteins that could diminish the effects of tea on cellular level and on vasodilation in rat aortic rings. By adding each milk protein individually in equal amounts to tea, these experiments were able to show which of the various milk proteins were inhibiting the vasodilatory effects of tea on isolated aortic rings and on NO production on endothelial cells. Since only the group of caseins actually prevented the effects of tea in vitro, our experiments evidenced that caseins complexed the physiologically active compounds in tea, long before the beverage reached the digestive tract in the body.
References
- Schroeter H, Heiss C, Balzer J, Kleinbongard P, Keen CL, Hollenberg NK, Sies H, Kwik Uribe C, Schmitz HH, Kelm M. (–)-Epicatechin mediates beneficial effects of flavanol-rich cocoa on vascular function in humans. Proc Natl Acad Sci USA (2006) 103:1024–1029.
[Abstract/Free Full Text] - Vlachopoulos C, Aznaouridis K, Alexopoulos N, Economou E, Andreadou I, Stefanadis C. Effect of dark chocolate on arterial function in healthy individuals. Am J Hypertens (2005) 18:785–791.[CrossRef][ISI][Medline]
- Whelan AP, Sutherland WH, McCormick MP, Yeoman DJ, de Jong SA, Williams MJ. Effects of white and red wine on endothelial function in subjects with coronary artery disease. Intern Med J (2004) 34:224–228.[CrossRef][ISI][Medline]
- Hodgson JM, Burke V, Puddey IB. Acute effects of tea on fasting and postprandial vascular function and blood pressure in humans. J Hypertens (2005) 23:47–54.[CrossRef][ISI][Medline]
- Duffy SJ, Keaney JF Jr, Holbrook M, Gokce N, Swerdloff PL, Frei B, Vita JA. Short- and long-term black tea consumption reverses endothelial dysfunction in patients with coronary artery disease. Circulation (2001) 104:151–156.
[Abstract/Free Full Text] - van het Hof KH, Kivits GA, Weststrate JA, Tijburg LB. Bioavailability of catechins from tea: the effect of milk. Eur J Clin Nutr (1998) 52:356–359.[CrossRef][ISI][Medline]
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