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Lots of studies suggest that drinking tea is good for you. Researchers have demonstrated beneficial effects on your heart and blood pressure. Compounds in tea might even help you keep the pounds off. But, and this is bad news for me, some scientists now believe that adding milk to your tea may diminish those benefits. NPR's Allison Aubrey reports.

ALLISON AUBREY, BYLINE: Tea connoisseur, Robert Rex-Waller, has a few strong opinions about what makes for a perfect cup of tea.

ROBERT REX-WALLER: I have just a small electric kettle.

AUBREY: As steam rises up in the tea room here at the Park Hyatt Hotel in D.C. where Rex-Waller overseas tea service, he waits for the moment when just a few bubbles start to form.

REX-WALLER: I believe in not boiling it over.

AUBREY: So really you don't want it to reach a full boil?

REX-WALLER: I don't want it to reach a full boil.

AUBREY: Where are we temperature wise?

REX-WALLER: We're probably at about 130, 140.

AUBREY: Anything hotter may be too harsh, he says, for the classic Chinese green tea he's serving up. It's called Dragon Well, and after he scoops some tea leaves into an infuser and adds water, he's ready to taste what he's come to appreciate as a very distinctive flavor.

REX-WALLER: I mean this has a, for me, a very spinachy flavor. And you can really see that the, this great, bright green chlorophylls all still there, I mean it's got this, I don't know if you can smell it?

AUBREY: Oh, I can definitely smell that. You get the sort of spinachy-seaweed essence.

REX-WALLER: Right, exactly.

AUBREY: This is the taste of pure, unadulterated green tea, Rex-Waller says. And you certainly don't need to add milk or sugar to it.

REX-WALLER: There are some teas where I would cringe a little bit if someone poured milk into them.

AUBREY: After studying in China, Rex-Waller says he adopted the tea customs he learned there.

REX-WALLER: A Chinese person would not add any milk to that tea. I think it would be considered sacrilegious to a point.

AUBREY: Sacrilegious.

REX-WALLER: Well, someone who's making these teas - they're really pouring their soul into it, so to take away from that I think would just be, would dishonor the tea.

AUBREY: The case for pure tea, unadulterated by milk, may be a struggle in a society that has a communal sweet tooth and maybe a penchant for cream. Even Starbucks serves up a sweetened green tea latte with steamed milk. But researchers who study the potential health benefits of tea, say the Chinese way may be the best way to go. Dutch researcher Rick Hursel of Maastricht University is convinced.

RICK HURSEL: We always recommend two to three cups a day in between meals. No milk. That's my recommendation.

AUBREY: Hursel and his colleagues study compounds in tea called flavonols, which are thought to be beneficial. One type of flavonol in green tea, called catechins, are the focus of a lot of research these days. Black tea has similar compounds. What Hursel has demonstrated in small short term studies, is that these catechins may have a positive influence on body weight regulation. Meaning they may slightly modify a person's metabolic set point.

HURSEL: We've shown that green tea is able to increase your energy expenditure, so the amount of calories you burn, and also to increase the amount of fat you are burning.

AUBREY: Now, before you get too excited, it's important to point out here that the effects are very small and perhaps only fleeting. More research is needed to determine whether this holds up in a significant way. But Hursel says the interesting thing is that when they add milk to the tea, the metabolic effects seem diminished.

HURSEL: Something happens which we don't want to happen.

AUBREY: Hursel says it's not exactly clear what. The theory is that the proteins in the milk bind or stick to the beneficial catechins, making it tough for the body to absorb them efficiently. And this has also been observed among scientists who study tea's effect on blood vessel health. Flavonols in tea seem to play a role in helping regulate blood pressure, at least in preliminary studies. But the effect may be diminished when milk proteins or other types of protein are eaten with it. Now, not all scientists are convinced that the effect of milk is strong enough to cancel out potential health benefits.

ALAN CROZIER: There is no convincing evidence that milk's a problem.

AUBREY: That's researcher Alan Crozier of Glasgow University. He says, given the very high levels of flavonols in tea, and the very small amount of milk added to a typical cup of tea, the effect is likely minimal.

CROZIER: The amount of milk is not going to greatly interfere with the way they're absorbed. The fats in the milk might slow down the absorption, but there's no evidence that they cause irreversible binding and stopping the bioactive compounds being absorbed.

AUBREY: Whether it's dictated by tradition or potential health benefits, Robert Rex-Waller of the Park Hyatt Hotel says, really, people should enjoy tea the way they like it.

REX-WALLER: I used to scoop sugar onto everything there was. And so everyone has their own preference.

AUBREY: He says if you prefer black tea with milk and sugar, one idea is to have that with breakfast. Then later in the day, try to add in a cup of green tea sans milk and sugar. Allison Aubrey, NPR News.

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