European Heart Journal Advance Access originally published online on April 28, 2007
European Heart Journal 2007 28(10):1265-1266; doi:10.1093/eurheartj/ehm092
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Addition of milk prevents vascular protective effects of tea
Department of Physiology and Biochemistry of Nutrition
Federal Research Centre for Nutrition and Food
Location Kiel
Hermann-Weigmann-Str. 1
Kiel 24103
Germany
Department of Physiology and Biochemistry of Nutrition
Federal Research Centre for Nutrition and Food
Location Kiel
Hermann-Weigmann-Str. 1
Kiel 24103
Germany
Tel: +49 431 609 2234 fax: +49 431 609 2472 E-mail address: maria.pfeuffer{at}bfel.de
The paper of Lorenz et al.1 concludes that milk may counteract the favourable health effect of tea on vascular function. Impaired vasodilation is one of the mechanisms underlying hypertension. We agree with the authors in that all dietary components should be considered, and that potential interactions should be examined when interpreting effects.
We, however, would like to address two major aspects. That there was a significant positive effect of a large serving of tea on vasodilation is plausible considering what we know about the biological function of tea ingredients and phenolic compounds in other foods. It was, however, minor in absolute terms, just 3.5% above the control response. It is open how long the effect would last and what it could mean for the vasodilatory response throughout a whole day.
The authors then assumed that the inhibitory effect (or rather non-stimulatory) effect of tea if consumed together with milk might be caused by casein complexing the tea catechins. If such a complex is formed in the intestinal tract, would catechins remain complexed once casein is broken down to amino acids and peptides? We doubt this. Casein is a well-digestible protein. But casein forms a curd in the stomach. Release into the small intestine is delayed in comparison with other proteins, like whey proteins. When milk was fed to miniature pigs, whose gastrointestinal physiology is reasonably close to that of humans,2 the majority of proteins consumed was still in the stomach after 2 h of intake. Milk processing influenced the degree of retention.3 Therefore, complexed tea catechins might also remain in the stomach for an extended time, but would probably be released and absorbed later on, influence vasodilation at a later time post-prandially, and last longer. Of note, milk does not necessarily delay catechin absorption. When 25% milk was added to coffee, up to 40% of chlorogenic acid were bound to milk proteins, but these interactions tended to decrease during in vitro gastric and intestinal digestion.4 When ingested with a regular breakfast, there was no different appearance of catechins in blood between tea alone and tea with 100 ml of milk.5 Lorenz et al.1 served tea or tea plus milk with a croissant. We advise to perform repeated tests of the post-prandial vasodilatory response to tea and tea plus milk, at least up to 6 h. We would also suggest to perform an additional test with milk alone (plus water) as a control.
A major focus of research is on the health effects of dietary fats. Dietary fats mostly impair post-prandial vasodilation, but a number of substances, for example polyphenols from olive oil6 have the potential to prevent this impaired response or even improve vasodilation above the fasting level. Concurrent consumption of soy protein or casein did also prevent the fat-induced impaired vasodilation.7 In experiments of our group, a fat-rich mixed meal containing casein did not impair post-prandial vasodilatation (unpublished results). In fact, milk products seem to have beneficial effects of their own. A number of epidemiological studies observed an inverse correlation between consumption of milk and milk products and hypertension, and several intervention studies demonstrated a reduction of blood pressure with consumption of milk and milk products.8 Milk is rich in calcium and other minerals and low in sodium, and vasoactive peptides are encrypted in milk proteins. A trial within the so-called DASH programme (Dietary Approach to Stop Hypertension) showed that a diet rich in fruits, vegetables, and low-fat milk products reduces blood pressure significantly better than a fruit and vegetable diet alone, in individuals with both optimal and elevated blood pressure. Inclusion of dairy products nearly doubled the effect.9 Therefore, before drawing premature conclusions, one should carefully examine the diet context.
The cell culture results look impressive, but in vivo endothelial cells are not exposed to casein or other milk proteins. The observed protein effects are dictated by physicochemical properties. Such studies give no meaningful information.
References
- Lorenz M, Jochmann N, van Krosigk A, Martus P, Baumann G, Stangl K, Stangl V. Addition of milk prevents vascular protective effects of tea. Eur Heart J. doi:10.1093/eurheartj/ehl442.
- Barth CA, Pfeuffer M, Scholtissek J. Animal models for the study of lipid metabolism, with particular reference to the Göttingen minipig. J Animal Physiol Animal Nutr (1990) 20(suppl. 20):39–49.
- Meisel H, Hagemeister H. Influence of different technological treatments of milk on digestive processes in the stomach. II. Gastrointestinal passage of milk components (Zum Einfluss unterschiedlicher technologischer Behandlung von Milch auf die Verdauungsvorgänge im Magen. II. Magenpassage verschiedener Milchinhaltsstoffe). Milchwissenschaft (1984) 39:262–266.
- Dupas CJ, Marsset-Baglieri AC, Ordonaud CS, Ducept FMG, Maillard MN. Coffee antioxidant properties: effects of milk addition and processing conditions. J Food Sci (2006) 71:S253–S258.[CrossRef][ISI]
- 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]
- Ruano J, Lopez-Miranda J, Fuentes F, Moreno JA, Bellido C, Perez-Martinez P, Lozano A, Gomez P, Jimenez Y, Perez Jimenez F. Phenolic content of virgin olive oil improves ischemic reactive hyperemia in hypercholesterolemic patients. J Am Coll Cardiol (2005) 46:1864–1868.
[Abstract/Free Full Text] - Westphal S, Taneva E, Kastner S, Martens-Lobenhoffer J, Bode-Boger S, Kropf S, Dierkes J, Luley C. Endothelial dysfunction induced by post-prandial lipemia is neutralized by addition of proteins to the fatty meal. Atherosclerosis (2006) 185:313–319.[CrossRef][ISI][Medline]
- Pfeuffer M, Schrezenmeir J. Milk and the metabolic syndrome. Obes Rev (2007) 8:109–118.[ISI][Medline]
- Appel LJ, Moore TJ, Obarzanek E, Vollmer WM, Svetkey LP, Sacks FM, Bray GA, Vogt TM, Cutler JA, Windhauser MM, Lin PH, Karanja N. A clinical trial of the effects of dietary patterns on blood pressure. DASH collaborative Research Group. N Engl J Med (1997) 336:1117–1124.
[Abstract/Free Full Text]
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