CHINA GREEN TEA is the second most consumed drink world […]
CHINA GREEN TEA is the second most consumed drink worldwide, following water, but there is an abundance of beverage options, so tea consumption lags behind soft drinks, bottled water, beer, milk, coffee and fruit drinks.
At Cooper Aerobics, everything always begins and ends with science. How much science is there–lots of research or very little? Is the research primarily with mice or people? How long and large are the studies?
Across multiple studies, are the findings generally positive? Are there any “red flags” where the ingredient was found to have a potentially serious negative affect on any group of people? And is there a fairly clear idea of what the appropriate “dose” should be in generally healthy people, to positively impact health? Building a body of research on an ingredient takes years, but if the science doesn’t support it, it will not be added. With these questions in mind, we’ve done research about tea.
All tea – black, white, oolong and green, come from the same camellia sinensis plant. During processing, the tea leaves are wilted, rolled and left in a humid environment to promote enzymatic changes. The difference between the varieties is essentially how long the tea stays in this humid environment and how much oxygen the leaves absorb. Tea is an antioxidant, and oxygen oxidizes it, exactly the same way sliced apple starts to brown and eventually turns black, the longer it is left out. Black tea has been exposed to the most oxygen during processing and is most oxidized, while white tea has been exposed to the least amount of oxygen and is lightest in color. Between white and black tea, there’s green tea, which is un-oxidized and oolong tea, which is partially oxidized. Herbal tea actually isn’t a tea at all – it’s simply a blend of dried flowers, fruits and herbs.
Green tea processing involves withering and steaming with no fermentation of the tea leaf, while oolong tea is semi-fermented, and black tea is fermented. All tea contains polyphenols, powerful antioxidants that may neutralize free radicals, The polyphenols in tea are classified as catechins. While there are six primary catechin compounds, the most abundant is epigallocatechin 3-o-gallate (EGCG), and green tea has more of these catechins, as fermentation for oolong and black teas reduces their levels.
Tea Health Benefits
There is good research supporting tea, particularly green tea and it’s positive impact on health. The Archives of Internal Medicine published a study in January 2012, reporting that three cups of green tea showed drops in systolic and diastolic blood pressure.
The April 2012 Tufts Nutrition letter reported on research conducted at the University of Western Australia in Perth that found the group who drank three cups of black tea daily saw an average drop in systolic pressure of two to three points, and about a two point drop in diastolic pressure compared to the control group who did not consume tea (but did consume caffeine) over a six month period. Previous research on tea found the polyphenols in tea can improve the function of the cells that line the interior of blood vessels. Other studies link these antioxidant compounds to reductions in abdominal fat and body weight which can also affect blood pressure.
In June 2012, Environmental Nutrition reported that green tea “appears to reduce inflammation and pain in arthritis.”
Pennsylvania State University Researcher Joshua Lambert, PhD, studies dietary phytochemicals (including the polyphenols derived from tea, and their impact on obesity and fatty liver disease. In a mice study, Dr. Lambert fed a group of obese mice a green tea compound (equivalent to 10 cups of green tea in humans) along with a high-fat diet for six weeks. The control group simply ate the high-fat diet, and the study found that the mice who also received the green tea compound gained weight 45 percent more slowly than the control group. The mice receiving the compound also had almost a 30 percent increase in fecal lipids, so potentially green tea limits fat absorption. Dr. Lambert says “There seem to be two prongs to this – first, (the compound) reduces the ability to absorb fat, and second, it enhances the ability to use fat.”
A 2010 study reported in the American Journal of Clinical Nutrition, found that one cup of green tea, containing 45 mg caffeine and 200 mg EGCG, had a “small effect on weight loss.” The September, 2011 issue of Environmental Nutrition reported that preliminary evidence suggests 270 mg ECGC (green tea extract) helps burn an extra 50 to 100 calories a day in overweight individuals who are also following a reduced-calorie diet.
Green Tea Health Recommendations
Cooper Clinic Registered Dietitians understand the positive health effects of green tea (and generally tea overall), and offer these suggestions about tea:
Drink tea. While all types of tea are good, green tea has the highest level of catechins and is the most commonly preferred tea.
Aim to drink two eight-ounce cups of green tea twice per day. In reviewing the research, a “cup” of tea is not a standard eight ounces. A review of many studies had “cup” sizes as small as 3.4 ounces.
Drink what you like. Different brands and forms of tea all taste a little bit different. Many grocery stores include tea in their bulk areas. Loose tea usually has more flavor and this can be a good, affordable option, as well as a way to experiment with a variety of blends.
Tea freshness counts. The level of EGCG and the other catechins falls dramatically as the tea ages. Green tea leaves that are six months old have EGCG levels almost 30 percent lower than fresh leaves.
It matters what you add to your tea. A bit of lemon or other citrus fruits helps the body absorb the catechins, while adding milk can bind with the catechins in the tea and make it difficult for the body to absorb.
Green tea is delicate. While black tea is best brewed in boiling 212 degree water, the catechins in green tea, as well as oolong and white tea, are damaged when prepared in water that is more than 180 degrees. This can be a difficult problem, as electric kettles heat water to boiling and Keurig® systems brew at 192 degrees, although the newest systems allow the temperature to be adjusted down to 187 degrees.
Caffeine in tea varies. The length of steeping, the type of tea and even the location of the leaf on the actual tee plant, all play a role in the caffeine level in tea. Green tea typically has 24 to 40 mg caffeine per eight ounce cup, where black tea averages 14 to 61 mg.
Green Tea Supplement Concern
With all this good news, what is the issue? While EGCG has a long history of being safe in the diet, researcher Dr. Lambert is concerned about the much higher doses of EGCG found in green tea supplements. Dr. Lambert’s lab has discovered that mice given high-dose EGCG developed liver damage.
The American Institute for Cancer Research (AICR’s) second expert report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, cautions that very high amounts of green tea, typically found from supplement use, can negatively interact with drugs that affect blood clotting, including aspirin.
In 2010, the European Food Safety Authority suspended their endorsement of antioxidant health claims in food, including green tea. The endorsement was removed as much of the positive research has been conducted in laboratories and animal studies.
Potential liver damage and issues with blood clotting are huge. When he talks about green tea benefits, Dr. Lambert stresses that “natural” does not always mean safe, and that “there are things in the diet that have biological activity that can be either good or bad, depending on the dose. It’s that issue of ‘if something’s good, more isn’t always better.”
We continually reevaluates their product line and examines the latest scientific research. At this time, there are no plans to offer green tea supplements in the supplement line. There needs to be long-term studies with green tea consumption and consumption of green tea extract, to determine if the antioxidants of green tea, in either tea or extract form, are truly beneficial to health.