I'm a serious tea drinker. I'll down it hot or cold, plain or with lemon. Like most Americans, however, I don't regularly add milk. But when my colleague David Lindley, an editor here at Science News, was growing up, his family certainly did.
Being a Brit, David comes from a culture that holds considerable reverence for this brew and might be accused of being fussy about its preparation. When I add milk to tea, which I do only occasionally, I'm not careful about the amount. It's typically a big slosh—and always added after the tea is fully brewed and sitting in a mug.
In the Lindley household, by contrast, "a little milk was put into the bottom of a cup—just a touch," before any tea was added, David notes. And his mom invariably made tea in the pot, brewing it from some black, loose-leaf variety.
Because adding milk to tea is routine in the United Kingdom, a team of Scottish researchers decided to investigate the potential health significance of this practice. Their concern: Because milk can bind to some of tea's antioxidants, it might prevent them from countering free radicals.
These radicals can wreak havoc on DNA and other components of cells. And with the onslaught of age, disease, and pollutant exposures, our bodies find it harder to keep those radicals in check. The result: Studies have begun linking excessive free-radical production to a host of chronic disorders, from cancer and diabetes to heart disease.
Against this backdrop, Janet A.M. Kyle and her colleagues at the Rowett Research Institute purchased different teas from local stores, brewed them up, and then assayed their antioxidant activity. In a paper published online and in the June 13 Journal of Agricultural and Food Chemistry, they report finding some brand-related differences in the inherent antioxidant activity of a brew. The good news: Adding milk doesn't alter that activity.
Moreover, they found, adding milk to tea doesn't diminish the amount of antioxidants—such as the epigallocatechin gallate, which many commercial teas tout as EGCG—that ends up in tea-drinkers' blood. So, it appears one can safely boost the protein content of your brew, by adding milk, without sacrificing tea's antioxidant bounty.
Rich in antioxidants
When it comes to quashing free radicals, tea provides an antioxidant bonanza. Best known are its catechins, a family of compounds whose star, EGCG, has been linked not only to weight loss but also to diminished cancer risk.
Teas also contain polyphenolic chemicals, another class of antioxidant compounds that appear capable of lowering an individual's risk of heart disease and cancer. Tea's chief polyphenol constituents are quercetin and kaempferol. However, because milk can bind to these, there had been concern that such chemical pairings might limit the polyphenols' biological activity or even their uptake by the body.
To test that, Kyle's group purchased six locally popular teas and evaluated the composite antioxidant activity of each. They boiled water and added 3 grams of tea leaves—the amount in a typical U.K. tea bag, but 50 percent more than is found in typical European tea bags—for each brewed cup. Chemical assays showed that the brews' levels of polyphenols and catechins rose steadily for about 7 minutes.
"Except for the cheapest supermarket brand," Kyle notes, "we got similar results for these teas." The low-cost outlier proved lower than the name brands in terms of the free-radical-quenching punch it delivered, mostly owing to its low concentrations of polyphenols.
The researchers selected the tea that had exhibited the strongest antioxidant performance for their follow-up human trials. On three separate occasions, each of 9 healthy men in their mid-20s to mid-30s avoided tea for at least a day, fasted overnight, and then drank a test beverage for breakfast.
On one morning, each man got two cups of black tea that had been steeped for 7 minutes. Together, the cups contained 300 ml of tea mixed with 100 ml of hot water. Another day, volunteers got 300 ml of tea mixed with 100 ml of skim milk. On the remaining test day, each recruit downed 300 ml of hot water that had been doctored with 100 ml of milk. (Didn't the latter taste ghastly? "It did," Kyle concedes, "and I'm very grateful to my volunteers for actually drinking it.")
Before and at various points over a 3-hour period following the consumption of each day's beverage, Kyle's group sampled the volunteers' blood to measure polyphenols, catechin levels, and the blood's ability to quash free radicals. While the gross, milky hot water had no effect on these parameters, both brews showed equivalent increases in circulating antioxidants and radical-thwarting prowess, which peaked about 60 minutes after tea had been consumed.
Kyle says her group now hopes to examine tea's antioxidant performance in a larger group of people and for a longer period. She's hoping it proves substantial because the only other source of the antioxidant chemicals being looked at in her study come from fruits and vegetables—and "we don't eat a lot of those in Scotland," she says, "but we do drink a lot of tea."
And what about David: After 24 years in the United States, does he still blend a touch of milk with his tea? No, he says. Milk is for black tea, which doesn't much agree with his constitution. Today, his brews are "mostly green and herbal teas."
By the way, David's not just one of our editors. The author-physicist also has 6 books under his belt. On Feb. 20, Doubleday published his latest—Uncertainty: Einstein, Heisenberg, Bohr, and the Struggle for the Soul of Science.
Editor's note: David Lindley played no role in assigning or editing this article.
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Janet A.M. Kyle
Rowett Research Institute
Aberdeen AB21 9SB
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