Biotech Values

[ThomasS]

o/t: Tea enthusiasts: For Vascular Benefit of Black Tea, Hold the Milk ( I mix together black tea with green tea to cover all bases; there are known benefits from both }

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
BERLIN, Jan. 9 -- Black tea's purported cardiovascular benefits are blunted when milk, even skimmed milk, is mixed into the brew, found researchers here. Action Points

Advise patients who ask that the results of this small, preliminary study must be confirmed by larger studies.
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.