Globally, in terms of its popularity as a drink, tea ranks second only to water. While most people began sipping this brew for its taste and its ability to sooth the palate, researchers have recently turned up a variety of reasons to reinforce tea-quaffing habits. The newest: It slows the growth of germs that lead to cavities.
Take a microscopic look into any healthy mouth and you’ll probably find hundreds of species of bacteria. Some of these generate an enzyme that breaks down sucrose, or table sugar, into its building blocks—the simple sugars fructose and glucose. Others foster the conversion of glucose into long, sticky chain-like units, called glucan molecules.
Glucan helps cement diverse communities of bacteria (SN: 7/14/01, p. 28) onto the surfaces of our teeth, forming dental plaque. When it’s not flossed or brushed off, microbes living in the plaque mine it for bits of food that collects in its goo. As bacteria digest the food, they produce acids, which dissolve tooth enamel.
Initially, these acids pit a tooth’s surface. Over time, however, the erosions can deepen and expand into tiny craters that become visible to the naked eye. These are the cavities that trigger your dentist to reach for the drill.
However, new studies indicate that black tea—the primary type drunk throughout the West—can short-circuit this process by depressing the activity of the initial sucrose-degrading enzyme.
It takes fairly prolonged exposure for the tea to work its magic, according to data presented recently at the American Society of Microbiology annual meeting in Orlando, Fla. In one study, Christine D. Wu of the University of Illinois College of Dentistry in Chicago divided 20 volunteers into three groups. Some rinsed their mouth with water five times over a 15-minute period, with each rinse lasting a full 30 seconds. Others did the same thing, substituting black tea. A third group rinsed their teeth with tea, but only once for a half-minute.
A single rinse with tea had no effect on the plaque bacteria nor did rinsing more frequently with water. However, rinsing with tea five times daily clearly inhibited plaque bacteria. Notes Wu, “They grew more slowly”—and made less acid.
In a second, week-long study headed by her colleague, Peter Lingström at Göteborg (Sweden) University, men and women swigged and swished tea around their mouth for a minute. Some did it 5 times a day, others 10 times. As in Wu’s shorter test, the higher-frequency rinsing had a more profound effect. People in this group showed fewer cavity-forming bacteria in their plaque, and their plaque became less acidic.
Wu and James S. Wefel, director of the University of Iowa’s Dows Institute for Dental Research in Iowa City, also looked at the impact of tea on the fluoride levels in teeth. Tea contains fluoride, and fluoride protects teeth from plaque bacteria. Overall, people in the group with the more frequent tea exposure developed a somewhat enriched store of fluoride inside their plaque. However, a subsequent test-tube study with extracted human teeth showed that the amount of fluoride delivered by tea was not sufficient to help rebuild teeth already pitted by plaque-generated acids.
A component of tea that may play a more important role in protecting teeth is an antioxidant known as epigallocatechin gallate—or EGCG, for short. This catechin belongs to the class of chemicals known as polyphenols. Though there are potentially hundreds of polyphenols, Wu’s studies indicate that “this one works.” Other catechins “also work, but not as well,” she told Science News Online.
“We’re now trying to look at what else is active in black teas,” Wu says, and she will begin testing tea-free catechins as a rinse. The latter might be a boon for those who value a bright smile, because these unpigmented chemicals wouldn’t stain teeth the way the whole brew does.
Indeed, Wu acknowledges, people who prefer their tea with milk or cream may defeat the cariostatic action of the brew by binding up the active agents.
“We just don’t know, yet,” she says.
Green tea, oolong, and black tea all come from the same plant. The distinctive difference in their tastes traces to how the leaves were processed.
Wu notes that a lot more work has focused on the benefits of green tea, which is extremely popular in Japan and China. For instance, this tea appears to fight cancer (SN: 2/2/99, p. 15) and to reduce the formation of caries—both in animal studies and in people. The London-based Tea Trade Health Research Association, which funded Wu’s work, now wants to see whether black tea, the type preferred in Great Britain and North America, works similarly.
The bottom line: If you like green tea, don’t switch to black just in hopes of helping your teeth.
Looking for more incentives to up your tea consumption?
A new study in the July 10 Circulation documents a strong link between drinking black tea and artery health among people with existing heart disease. Indeed, in the 50 patients they studied, Joseph A. Vita of Boston University’s Whitaker Cardiovascular Institute and his colleagues found that those who were given tea showed some reversal of their endothelial impairment and improved dilation of their vessels.
Also this month, a team of Kentucky scientists showed that green tea polyphenols—including EGCG—ratcheted down the chronic inflammation experienced by mice suffering from an experimentally induced colitis, a type of inflammatory bowel disease. In this study, mice didn’t drink tea, just water to which tea polyphenols had been added. In the Journal of Nutrition, Craig J. McClain of the University of Louisville and his coworkers conclude that because these polyphenols tempered inappropriate inflammatory reactions in the gut, they “may have clinical significance in the [human] treatment of Crohn’s disease.”
Finally, an epidemiological study reported in the May 15 International Journal of Cancer finds that heavy green tea drinkers in China were half as likely to develop chronic stomach inflammation or stomach cancer as were people who eschewed the brew.
So, will it be green or black? One lump or two?