Tuesday, December 4, 2012
Tea’s health benefits look promising
The washington Post
A tea timeout is my favorite way to de-stress. It feels so civilized to relax with a warm cup of jasmine-scented green tea or perhaps the traditional English treat, black tea with milk — white, as they say. Still, with all the myths we hear about nutrition, I’ve always wondered, is tea as healthful as many people believe?
Although tea has been enjoyed around the world for some 5,000 years, it wasn’t until relatively recently that scientists started searching for the facts.
From the 1970s to the 1990s, epidemiological studies — the kind following large populations’ eating and disease patterns — found that drinking tea might be associated with better health. No clear cause-and-effect relationship between health and tea was established, though.
“More careful clinical and laboratory studies are needed,” said Johanna Dwyer, a professor at Tufts Medical School in Boston, at the fifth International Scientific Symposium on Tea and Human Health, held Sept. 19 at the U.S. Department of Agriculture.
Recent studies have been promising. What did they find? Just about every cell in the body could potentially benefit from tea, with virtually no downsides.
All true tea (white, green, oolong and black, as opposed to herbal varieties) comes from one plant: Camellia sinensis. The differences are in how they are processed, with white and green being the least processed, oolong in the middle and black the most processed. The processing changes the nutritional profile and some of the health effects. No matter the process, all tea leaves are dense with flavonoids, health-promoting chemicals found in fruits, vegetables, whole grains and most plants.
“About one-third of the weight of a tea leaf is flavonoids, which is high, especially when you consider there are virtually no calories,” said Jeffrey Blumberg, professor of nutrition science and policy at Tufts University and chairman of the tea symposium. “A serving of tea is like adding a serving of fruits or vegetables to your diet.”
Can tea produce more health benefits than fruits or vegetables? Flavonoid research results are exciting but mixed.
There are “small but possibly significant health effects, but study quality needs to improve. … The variety, geography, processing and brewing of tea must be considered since it will dramatically change flavonoid content and possibly associated health benefits,” Dwyer said. “Tea is not a drug, and to expect a druglike effect is unrealistic.”
The exciting news about tea includes:
It helps your heart by keeping blood vessels unclogged and flexible. Blood pressure and stroke risk were reduced in epidemiological and clinical studies (even with sugar added).
In one study in which hypertensive men drank one cup of black tea daily, both systolic and diastolic blood pressures fell. The blood-pressure-lowering effect was maintained even after a large intake of fatty, sugary food, which usually constricts blood vessels, showing that “cardiovascular protection can be achieved even without much sacrifice and with normal intakes,” said Claudio Ferri, a professor at Italy’s University of L’Aquila School of Internal Medicine and co-author of the study.
Healthier blood vessels create better blood flow, which means all of your organs, including the brain, receive more blood, oxygen and nutrients, enhancing your body’s ability to fight disease.
It improves bone health. After drinking four to six cups of green tea daily for six months, post-menopausal women with low bone mass (osteopenia) achieved an improvement in certain short-term measures of bone health in a National Institutes of Health-funded study conducted at Texas Tech University Health Sciences Center. They also improved muscular strength. Tea reduced oxidative stress and inflammation, preventing the usual bone and muscle breakdown.
It can help your thinking. When your brain receives better blood flow and oxygen, and inflammation and oxidative stress decline, cognitive function improves, according to studies. In fact, a 25 percent reduction in impairments of activities of daily living was found when adults drank three to four cups of tea daily.
It might reduce cancer risk. Many animal and test-tube studies have found anti-cancer effects of tea, but human studies have been less consistent. “In lab studies, compounds in tea show a lot of cancer-fighting promise. Many act as antioxidants, slow tumor growth and even increase cancer cell death,” said Alice Bender of the American Institute for Cancer Research.
It can help you lose weight. Not only does tea have fewer calories than most beverages (zero without milk and sugar), but certain compounds in tea, and especially green tea, burn body fat.
Tea can help you de-stress. An amino acid called L-theanine, in combination with caffeine, might reduce stress. Studies have shown this combination, which occurs naturally in tea, reduces cortisol, the stress hormone, and improves mental alertness.
Katherine Tallmadge is a registered dietitian and author of Diet Simple: 195 Mental Tricks, Substitutions, Habits & Inspirations.
It’s tea time
“Tea catechins are stable in dry tea leaves but diminish as brewed tea is held/stored. To make sure you are consuming the tea phytonutrients (flavonoids) that may promote health, brew tea fresh,” nutritionist Beverly Clevidence of the USDA’s Agricultural Research Service said in an email. To maintain the healthful nutrients, keep tea leaves in an airtight container away from light and heat.
Many people believe tea dehydrates the body. But the National Academy of Sciences has refuted that, saying tea and coffee are as hydrating as water.
Some avoid tea because of its effect on iron absorption, but the effect is small. If you have iron-deficiency anemia, drink tea be- tween meals to minimize inter- ference, and eat your iron-contain- ing foods with vitamin C-contain- ing foods to maximize absorption.
Milk (or any protein, for that matter) might bind with and prevent absorption of some flavonoids but could enhance absorption of others. Studies have been too limited to determine the extent of the effect.
Drink tea throughout the day to keep the flavonoids in your system and get maximum benefit — various studies have suggested between one and six cups a day — and don’t forget a balanced diet.
Stick with the tea you enjoy most, whether white, green, oolong or black. All impart health benefits, and the studies are not detailed or numerous enough to choose one over another.
Be wary of bottled ready-to-drink teas or products containing tea extracts or supplements, as there is no way of knowing their flavonoid content, if any.