Plain Tea Is Fine

Brew A Healthy Ticker Studies suggest that drinking black tea can reduce your risk of heart attack and stroke. Chemicals in tea called catechins seem to increase the amount of nitric oxide produced in artery walls, helping your arteries to relax and expand (dilate), to accommodate blood as it's pumped from the heart. But a small study from Germany finds that adding milk may cancel out the cardio-protective effects of tea.

The researchers compared the effects of drinking boiled water and hot tea (both with and without milk-added) in 16 healthy women. They used ultrasound to measure how well arteries in the participants' forearms dilated before they drank tea and two hours afterwards. Compared to plain boiled water, black tea significantly improved blood flow, but when milk was added to the tea it blocked these effects. Lab tests in rats produced similar results.

Milk proteins called caseins decrease the amount of beneficial catechins in tea, the researchers reported in the European Heart Journal. They speculate that the findings could help explain why countries such as Britain, where milk is usually added to tea, have not shown a decrease in the risk of heart disease and stroke that could be attributed to tea drinking.

Since tea drinking is also linked to reduced risk of some cancers, the researchers called for further studies into the effects of milk on the activity of catechins. The data only applies to black tea is usually drunk without milk.

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