Add milk at your peril

New Delhi, Jan. 9: Tea drinkers may have to choose between flavour and health. A new study released today says adding milk to black tea wipes out its protective effect against heart disease.

The study by researchers in Germany has shown that proteins in milk interact with tea to decrease the concentrations of certain chemicals found in tea that protect against cardiovascular disease.

Milk counteracts the favourable health effects of black tea on the function of blood vessels, the researchers at the Charite Hospital in Berlin said, reporting their findings in the European Heart Journal.

“The addition of milk to black tea completely prevents its beneficial effect on the blood vessels,” cardiologist and principal investigator Verena Stangl told The Telegraph.

“This was a small study, but it provides us insights into mechanisms underlying this effect.”

“People who drink tea for health reasons might be better off by not adding milk,” she said in a telephone interview.

In their study, the researchers gave healthy postmenopausal women half a litre of freshly brewed black tea, black tea with 10 per cent milk, or just plain boiled water. They used ultrasound to examine the forearm artery of each volunteer before and two hours after the drink.

The scientists found that while drinking tea significantly increased the ability of the artery to relax and expand to accommodate increased blood flow compared with drinking water, the addition of milk eliminated this biological effect.

In recent years, medical studies have highlighted multiple health benefits of tea. “Our results provide a possible explanation for the lack of beneficial effects of tea on the risk of heart disease in countries where milk is usually added,” Stangl said.

Tea is the second most consumed drink in the world after water. But India and the UK are among several countries worldwide where people prefer to add milk to black tea.

Milk contains a large number of proteins and the researchers screened several proteins to discover that a class of proteins called caesins are responsible for interfering with the protective effects of tea. The caesins interact with compounds called catechins in tea that contribute to its protection against heart disease.

Stangl’s team explored the underlying mechanism of tea by studying its effect on rat hearts and found that tea relaxed the lining of arteries by producing nitric oxide.

“Tea activates an enzyme that leads to the release of nitric oxide, but this is completely blocked when milk is added to tea,” Stangl said.

The researchers caution that the findings relate only to black tea and not to green tea, which is almost exclusively consumed without milk.

While the addition of milk may improve the taste of black tea, it may also lower its heart-protective properties, said Mario Lorenz, a molecular biologist and team member.

While previous studies have also highlighted the protective effect of tea against cancer, Stangl said the new results may have implications for this effect too.