The Truth About the Health Benefits of Tea by Kate Lowenstein
Does it really fight cancer? Lower cholesterol? We filter
the research to find out which health claims actually hold
Blue Jean Images/CorbisThe way scientific studies and health
gurus alike have touted the perks of tea over the past few years,
you'd think the stuff was some kind of all-powerful magical elixir.
Improving heart health, reducing cancer risk, warding off dementia
and diabetes-there's barely a health benefit that hasn't been
credited to tea. It's true that the brew has disease-fighting
antioxidants, and, as far as anyone can tell, should be great for
us. "The science is certainly promising," says David L. Katz, MD,
director of Yale University's Prevention Research Center. "But the
hype goes beyond it and tends to make promises which the science
can't yet deliver." (No, tea probably will not cure depression,
eliminate allergies, or boost your fertility!) We talked to the
experts and weighed the studies to separate the truth from the
Why tea is so hot
First, a definition: When scientists talk about tea, they mean
black, green, white, or oolong teas-all of which are made from the
leaves of the Camellia sinensis plant. Herbal brews, like chamomile
and peppermint, are not technically considered tea; they're
infusions of other plants with different nutritional
characteristics. If you're not sure what kind you're drinking,
check the ingredients for the word "tea."
What makes the four tea types different from each other is the way
the leaves are prepared and how mature they are, which affects both
flavor and nutritional content. Black tea is made from leaves that
have been wilted (dried out) and then fully oxidized (meaning that
chemicals in the leaves are modified through exposure to air).
Green tea's leaves are wilted but not oxidized. Oolong tea is
wilted and then only partially oxidized, and white tea is not
wilted or oxidized at all.
All four types are high in polyphenols, a type of antioxidant that
seems to protect cells from the DNA damage that can cause cancer
and other diseases. It's the polyphenols that have made tea the
star of so many studies, as researchers try to figure out whether
all that chemical potential translates into real disease-fighting
punch. Most research has focused on black tea, which is what about
75% of the world drinks, and green tea, the most commonly consumed
variety in China and Japan. Green tea contains an especially high
amount of antioxidants-in particular, a type of polyphenol called a
catechin, the most active and abundant of which is
epigallocatechin-3-gallate (EGCG). That's why there are five times
more studies on green than black tea each year-and likely why
you're always hearing about the power of the green stuff, says
Diane L. McKay, PhD, assistant professor of nutrition at the Tufts
University Friedman School of Nutrition Science and Policy.
Boiling down the hype
Luzia Ellert/Getty ImagesThe
most promising claims about tea drinking include these perks:
- Cancer prevention: A 2009 review of 51 green
tea studies found that sipping three to five cups a day may lower
the risks of ovarian, colorectal, lung, and prostate cancers, but
not breast or other cancers, says lead author Katja Boehm, research
fellow at the Center of Integrative Medicine at the University of
Witten/Herdecke in Germany. As for black tea, the National
Institutes of Health (NIH) deems it "possibly effective" for
reducing the risk of ovarian cancer, and "possibly ineffective" for
lowering the risk of stomach and colorectal cancers.
- Brain benefits: Downing from one to four cups
of black or green tea a day has been linked with a lower risk of
Parkinson's disease, according to the NIH.
- Heart help: "Drinking tea may be helpful in
preventing or delaying certain risk factors of cardiovascular
disease, and lowering LDL (bad) cholesterol and triglycerides,"
says McKay. One Japanese study found that adults who drank five or
more cups of green tea per day had a 26% reduction in death from
heart attack or stroke compared with those who had one cup or less;
the effect was greater in women than in men.
More research needs to be done on other potential benefits. One
small study suggested that the catechins and caffeine in green tea
may give dieters a small metabolic boost that could amount to
burning a few dozen extra calories per day. There's also a slim
file on how drinking tea may help ward off osteoporosis and reduce
the incidence of cavities, due to the fluoride it contains. And
EGCG, that green-tea antioxidant, has been found to increase the
number of important immune-boosting cells (called regulatory
T-cells)-but only in one animal study.
All this sounds pretty compelling. So why aren't major health
organizations advising us to drink tea like crazy? It's a matter of
needing more hard-core evidence. "There are pearls of real promise
here, but they have yet to be strung," Dr. Katz says. "We don't
have clinical trials in human patients showing that adding tea to
one's routine changes health outcomes for the better." The vast
majority of the research conducted has been observational, meaning
scientists can't know if the medical boosts seen in tea drinkers
are definitely a result of that habit, or some other factor that
makes these people healthier. And many of the studies that have
looked at specific compounds in tea have been conducted in labs or
on animals, not on people. "These chemicals act as antioxidants in
a test tube, but they may not do the same in your body," explains
Emily Ho, PhD, associate professor in the department of nutrition
and exercise science at the School of Biological and Population
Health Sciences at Oregon State University. "You have to take the
claims with a grain of salt."
That said, experts agree that a daily cuppa, or five, won't hurt
you, and may well help fight disease. (If you're trying to limit
your caffeine intake, go for decaf-it has antioxidants too, though
fewer than the caffeinated kind.) "Tea is probably better than a
lot of other beverages," says Lona Sandon, RD, assistant professor
in the department of clinical nutrition at UT South-western Medical
Center and a spokesperson for the American Dietetic Association.
"Just make sure you've got other healthy lifestyle habits-you can't
count on tea alone to prevent cancer."
Source: Health.com November 2011
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