By Janet Raloff
From San Francisco, at the spring national meeting of the American Chemical Society
For years, researchers have been extolling green tea as a natural source of compounds that appear to fight cancer by protecting DNA. Now, scientists have identified a relatively rare tea that may offer DNA even more protection. The surprise: Some share of this brew’s anticancer activity may result from its caffeine content, about twice that of green tea.
Known for its pale hue and delicate flavor, white tea comes from the same plant, Camellia sinensis, as green and other true teas. What distinguishes white tea is the buds that it contains and the way that it’s processed—steamed, rather than fermented or roasted. Many of the plant’s potent cancer fighters, its polyphenol antioxidants, “become oxidized or destroyed as green tea is further processed into oolong and black teas,” explains Roderick H. Dashwood of Oregon State University in Corvallis. White tea undergoes even less processing than green, so he suspects that it might “be more beneficial” to health.
In one test, his team incubated bacteria in cultures containing white or green tea and then compared each brew’s ability to protect the bacterial DNA from damage by a heterocyclic amine known as IQ. This carcinogen can form in fried or broiled meats. “White tea was a much more powerful antimutagen than green tea,” reports Oregon’s Gilberto Santana-Rios, a coauthor of the study. Although its potency varied somewhat between tests, white tea was always more protective than green tea, sometimes by a factor of more than five.
The researchers then offered rats either tepid white tea or water as their only liquid for 8 weeks. Each rodent also received PhIP, the most common heterocyclic amine in well-done meats (SN: 4/24/99, p. 264: https://www.sciencenews.org/pages/sn_arc99/4_24_99/bob1.htm). PhIP triggers the development of colon abnormalities—aberrant crypt foci—that presage cancer.
Tea-drinking rats developed fewer foci than did animals slaking their thirst with plain water. Santana-Rios reports that lacing the water with caffeine in a concentration equal to that in the tea also protected rats against precancerous foci, though not nearly as much as white tea did.
