For Vascular Benefit of Black Tea, Hold the Milk

[Guest guest]

>

> BERLIN -- Black tea's purported cardiovascular

> benefits disappear when milk, even skimmed milk,

> is mixed into the brew, found researchers here.

>

> +++++

> Lorenz M, Jochmann N, von Krosigk A, et al.

> Addition of milk prevents vascular protective

> effects of tea. Eur Heart J. Advanced online

> publication January 8, 2007.

>

> http://eurheartj.oxfordjournals.org/cgi/content/abstract/ehl442v1

> http://eurheartj.oxfordjournals.org/cgi/content/full/ehl442v1

> http://eurheartj.oxfordjournals.org/cgi/reprint/ehl442v1

>

> ++++

>

> © The European Society of Cardiology 2007.

>

> Addition of milk prevents vascular protective effects of tea

> Mario Lorenz1, Nicoline Jochmann1, Amélie von

> Krosigk1, Peter 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 (AT) charite (DOT) de

>

>

> 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.

>

> Key Words: Endothelial function * Nitric oxide *

> Tea * Milk * Flow-mediated dilation

>

>

> Online ISSN 1522-9645 - Print ISSN 0195-668x

> 2006 European Society of Cardiology

>

>

> +++++

>

> For Vascular Benefit of Black Tea, Hold the Milk

>

> By Jeff Minerd, Contributing Writer, MedPage Today

> Reviewed by Zalman S. Agus, MD; Emeritus

> Professor at the University of Pennsylvania

> School of Medicine.

> January 09, 2007

>

> Action Points

>

> * Advise patients who ask that the results of

> this small, preliminary study must be confirmed

> by larger studies.

>

> BERLIN, Jan. 9 -- Black tea's purported

> cardiovascular benefits are blunted when milk,

> even skimmed milk, is mixed into the brew, found

> researchers here.

>

> In a study of 16 postmenopausal women, those who

> drank about two cups of black tea without milk

> had a greater than four-old increase in

> flow-mediated vasodilation from baseline in the

> forearm brachial artery (P<0.01), said Verena

> Stangl, M.D., of the Charité-Universitätsmediz in

> Berlin, and colleagues.

>

>

> However, those who drank a mix of 90% black tea

> with 10% skimmed milk had no more of an increase

> in vasodilation than if they had consumed two

> cups of hot water, Dr. Stangl and colleagues

> reported online today in European Heart Journal.

>

>

> "The most striking finding of our study is that

> addition of milk to black tea completely prevents

> the biological activity of tea in terms of

> improvement of endothelial function," the authors

> said.

>

>

> They cited evidence from experimental and

> clinical studies indicating that tea exerts

> antioxidative, anti-inflammatory, and

> vasodilating effects, "thereby rendering

> protection against cardiovascular diseases" the

> researchers said.

>

>

> However, they added, it was not known whether it

> mattered if milk were added to tea.

>

>

> The study of black tea and milk included healthy

> women whose average age was about 59. In

> crossover fashion, each participant consumed 500

> mL (about two cups) of freshly brewed black tea

> without milk, tea with 10% skim milk, and a

> control beverage of boiled water. Flow-mediated

> dilation of the forearm brachial artery was

> measured before consuming each beverage and two

> hours afterward.

>

>

> Consumption of tea without milk was associated

> with a more than 400% increase in flow-mediated

> dilation compared with boiled water (P<0.01).

> However, consumption of tea with milk resulted in

> the same flow-mediated dilation increase as that

> of boiled water, (P not significant), the study

> found.

>

>

> To determine which milk compounds might be

> responsible for inhibiting the vasodilatory

> properties of tea, the researchers performed a

> series of cell culture experiments with the six

> major single milk proteins.

>

>

> The experiments were conducted on isolated rat

> aortic rings and endothelial cell cultures. The

> researchers measured the amount of nitric oxide,

> a mediator of flow-mediated dilation, that the

> cell cultures generated in response to

> stimulation with each milk protein combined with

> black tea, compared with black tea alone and

> black tea with skim milk.

>

>

> Three of the milk proteins-alpha-casein,

> beta-casein, and kappa-casein-blunted nitric

> oxide production about as much as milk did. The

> three other proteins-alpha-lactalbumin,

> beta-lactoglobulin, and serum albumin-appeared to

> have no effect on nitric oxide production.

>

>

> "Our results thus provide a possible explanation

> for the lack of beneficial effects of tea on the

> risk of heart disease in the United Kingdom,

> where milk is usually added to tea," they said.

>

>

> The three casein proteins in milk may form

> complexes with certain flavonoids in tea, called

> catechins, and thereby block their vasodilatory

> effect, the researchers speculated.

>

>

> "In conclusion, milk may counteract the favorable

> health effects of tea on vascular function," the

> authors said. "The finding that the tea-induced

> improvement of vascular function in humans is

> completely attenuated after addition of milk may

> have broad implications on the mode of tea

> preparation and consumption."

>

> The study authors reported no financial support or conflicts of

> interest.

>

>

> Primary source: European Heart Journal

> Source reference:

> Lorenz M et al. "Addition of milk prevents

> vascular protective effects of tea." Eur Heart J.

> Advanced online publication January 8, 2007.

> ----

> --

> © 2004-7 MedPage Today, LLC. .

>

>

> http://www.medpagetoday.com/PrimaryCare/DietNutrition/dh/4826

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