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MONDAY, Jan. 8 (HealthDay News) -- Plenty of studies have suggested that tea is a boon for cardiovascular health, but new research has found that adding milk to your favorite brew negates those benefits.
The culprits in milk is a group of proteins called caseins that interact with tea, decreasing the concentration of catechin -- the flavonoids in tea that are responsible for its protective effects against heart disease, according to the study authors.
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"There are a lot of studies that show that tea is protective against cardiac diseases," said lead researcher Dr. Verena Stangl, professor of cardiology at the Charite Hospital, Universitatsmedizin-Berlin, in Germany. "If you look at the studies, you see that in Asia there are less cardiac diseases, but in England that's not the case. So the question is, is the addition of milk a reason for this difference between Asia and England, where tea is often taken with milk?" she said.
In the study, 16 healthy postmenopausal women drank either half a liter of freshly brewed black tea, black tea with 10 percent skimmed milk, or boiled water on three different occasions under similar conditions. The researchers then measured the function of the cells lining the brachial artery in the forearm, using high resolution ultrasound before and two hours after tea consumption.
Stangl's team found that black tea significantly improved the ability of the arteries to relax and expand. "But when we added milk, we found the biological effect of tea was completely abolished," she said.
Additional experiments on rat aortas and rat endothelial cells -- which line blood vessels -- found that tea relaxed the vessels. But adding milk blunted the effect.
"If you want to drink tea for its health effects, don't drink it with milk," Stangl said.
The study findings are published in the Jan. 9 online edition of the European Heart Journal.
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