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Illustration by REY RIVERA| Zoom
Judging by the headlines on health-news reports, it almost seems that if you drink enough green tea, you could live forever. In scientific journals and the popular press alike, this ancient beverage has been touted for benefits ranging from fighting cancer and heart disease to beautifying your skin and preventing cavities. How much of the recent excitement over green tea is science and not just hype?
Humans have been steeping tea leaves in boiling water for as long as a half-million years, according to archeological evidence. China and India, which were among the first cultures to cultivate tea plants, have traditionally used green tea as a stimulant (one cup contains about 30 mg. caffeine), diuretic, and astringent. Ancient medical practices credit green tea with protecting the heart, regulating blood sugar, improving digestion, sharpening the mind, and even treating flatulence.
Jeffrey B. Blumberg, PhD, of Tufts University in Boston, has researched the health effects of green tea. He has this to say, “As investigators continue to study the multiple effects that tea has on human health, more research supports tea’s potential in helping reduce the incidence of major diseases.” But despite the headlines, Blumberg adds, the health benefits of tea aren’t linked to the green variety: “Observational studies in Asia show benefits of green tea and observational studies in the US, UK, and the Netherlands show benefits of black tea. Herbal “tea,” however, is not included in such research showing benefits against chronic disease.
Green tea, like other varieties of true tea, comes from the leaves of the Camellia sinensis bush. All teas contain natural antioxidants, especially the class of flavonoids called catechins, thought to benefit the body not only by acting as antioxidants but by modulating biochemical pathways that alter gene expression. Unlike the more familiar black tea, which is fermented in a process that links many of its catechins into large compounds called oligomers, green tea is minimally processed: The leaves are simply withered and steamed, which preserves a much higher concentration of simple catechins. Green tea also retains more of its principal bioactive catechin, epigallo-catechin-3-gallate (EGCG).
Oolong tea is partly oxidized, with catechin levels between green and black tea. White tea is made from partly opened buds and young leaves, which are steamed and then dried. So white tea may contain a higher concentration of EGCG than green tea, but it is more expensive and has been less extensively studied.
Most of the modern evidence for green tea’s health benefits comes from population (epidemiological) studies, rather than from clinical trials. Such observational studies cannot prove cause and effect, however, and it could be that other factors are responsible for the apparent benefits of green tea consumption. In particular, most of the major studies have been done in Asia. Asian people also consume more fish and soy, while eating less red meat than in the typical Western diet. It can be challenging to separate the possible effects of the dietary differences from green tea.
Here’s what’s brewing in research on green tea:
• Cardiovascular benefits. In 2006, a large Japanese study found that people who drank five or more cups of green tea daily had a 26-percent lower risk of death from cardiovascular disease than those averaging less than one cup. The 11-year study of 40,350 adults, ages 40 to 79, showed that the association of green tea was particularly strong for reduced risk of clot-related strokes. Women seemed to benefit the most, possibly because Japanese men still commonly smoke cigarettes.
That same year, however, the US Food and Drug Administration (FDA) rejected a petition to allow green tea makers to promote cardiovascular benefits on their labels. In nixing the request for a “qualified health claim,” the agency said it reviewed more than 100 studies and found “no credible scientific evidence to support qualified health claims about the consumption of green tea and a reduction of a number of risk factors associated with cardiovascular disease.”
Subsequent evaluations of the evidence have been somewhat more positive. A 2008 meta-analysis of 133 studies of flavonoids and cardiovascular disease, while mostly negative about other antioxidant-rich foods, concluded that green tea reduced LDL (“bad”) cholesterol levels. To achieve clinically significant reductions, based on that analysis, you’d have to drink two to five cups of green tea daily.
In 2009, a review by the Cholesterol Treatment Center at Concord Hospital in New Hampshire concluded that “preliminary evidence supports the possibility that green tea catechins … may lower LDL.” And a British review found that “a positive effect of green tea catechins on vascular function is becoming apparent.”
• Fighting cancer. In 2005, the FDA also rejected a petition to label green tea as protective against breast, prostate, and other cancers. Since then, however, evidence has continued to trickle in. McGill University researchers in Canada have shown in the lab thatEGCG from green tea inhibits the growth of cancer cells. A Japanese study found that women with breast cancer were less likely to suffer a recurrence if they drank at least two cups of green tea daily. An analysis of 22 studies of green tea and lung cancer concluded that consuming two cups daily was associated with an 18-percent lower risk. And the Shanghai Women’s Health Study reported that participants who regularly drank green tea at the start of the study were 37 percent less likely to develop colorectal cancer over six years than those who seldom or never sipped it. Life-long green tea drinkers fared even better, with as much as a 57-percent relative risk reduction.
More recently, a 2009 review of the effectiveness of green tea in the prevention of cancers found that much of the evidence was inconclusive. “In selected areas,” however, “green tea was effective in slowing the progression of the earlier stages of cancer.”
• Weight control. Helping you lose weight might seem an unlikely benefit of green tea consumption, but several studies have shown that green tea has slimming power. More recently, researchers at the Povident Clinical Research Center in Indiana published results of a study in which 132 participants were split into two groups: Half received a beverage containing 625 mg. of green tea catechins plus 39 mg. of caffeine, while the rest drank a controlled beverage containing only the caffeine. For 12 weeks, participants engaged in at least 180 minutes per week of moderate exercise; calorie intake was kept the same between the two groups. Those in the catechin group tended to lose more weight and showed significantly greater lowering of abdominal fat as well as triglycerides.
A recent review of 15 similar studies concluded that green tea catechins with caffeine modestly reduced body mass index (BMI), body weight, and waist circumference, but not waist-to-hip ratio.
• Protecting against pneumonia. Among the latest proposed green tea benefit is the possibility that its antioxidants might help combat the growth of viruses and other microorganisms. That’s the suggestion of Japanese researchers who recently reported a link between green tea consumption and a reduced risk of dying of pneumonia, at least for women. The study, done at Tohuku University, found that women drinking five or more cups of green tea daily were 47 percent less likely to die of pneumonia, and even those sipping just a cup or so a day were at 41-percent lower risk. The same association was not seen in men, however.
• Keeping cells young. Finally, the notion that green tea might help you live if not forever, at least a little longer might not be so far-fetched. In another recent study, Hong Kong researchers reported that people who drank an average of three cups of tea daily had longer telomeres DNA sequences at the end of chromosomes that shorten with aging than those averaging a quarter-cup daily or less. The cellular difference corresponds to the equivalent of about five years of life, the researchers said, adding: “The antioxidant properties of tea and its constituent nutrients may protect telomeres from oxidative damage in the normal aging process.”
Diane L. McKay, PhD, another scientist at Tufts University, sums it up like this: “Taken altogether, the evidence certainly suggests that incorporating at least a few cups of green tea every day will positively affect your health … It’s not going to cure anything and shouldn’t be consumed as a drug, but it can complement an overall healthy diet.”
Source: Philippine Star
Humans have been steeping tea leaves in boiling water for as long as a half-million years, according to archeological evidence. China and India, which were among the first cultures to cultivate tea plants, have traditionally used green tea as a stimulant (one cup contains about 30 mg. caffeine), diuretic, and astringent. Ancient medical practices credit green tea with protecting the heart, regulating blood sugar, improving digestion, sharpening the mind, and even treating flatulence.
Jeffrey B. Blumberg, PhD, of Tufts University in Boston, has researched the health effects of green tea. He has this to say, “As investigators continue to study the multiple effects that tea has on human health, more research supports tea’s potential in helping reduce the incidence of major diseases.” But despite the headlines, Blumberg adds, the health benefits of tea aren’t linked to the green variety: “Observational studies in Asia show benefits of green tea and observational studies in the US, UK, and the Netherlands show benefits of black tea. Herbal “tea,” however, is not included in such research showing benefits against chronic disease.
Green tea, like other varieties of true tea, comes from the leaves of the Camellia sinensis bush. All teas contain natural antioxidants, especially the class of flavonoids called catechins, thought to benefit the body not only by acting as antioxidants but by modulating biochemical pathways that alter gene expression. Unlike the more familiar black tea, which is fermented in a process that links many of its catechins into large compounds called oligomers, green tea is minimally processed: The leaves are simply withered and steamed, which preserves a much higher concentration of simple catechins. Green tea also retains more of its principal bioactive catechin, epigallo-catechin-3-gallate (EGCG).
Oolong tea is partly oxidized, with catechin levels between green and black tea. White tea is made from partly opened buds and young leaves, which are steamed and then dried. So white tea may contain a higher concentration of EGCG than green tea, but it is more expensive and has been less extensively studied.
Most of the modern evidence for green tea’s health benefits comes from population (epidemiological) studies, rather than from clinical trials. Such observational studies cannot prove cause and effect, however, and it could be that other factors are responsible for the apparent benefits of green tea consumption. In particular, most of the major studies have been done in Asia. Asian people also consume more fish and soy, while eating less red meat than in the typical Western diet. It can be challenging to separate the possible effects of the dietary differences from green tea.
Brewing research
Here’s what’s brewing in research on green tea:
• Cardiovascular benefits. In 2006, a large Japanese study found that people who drank five or more cups of green tea daily had a 26-percent lower risk of death from cardiovascular disease than those averaging less than one cup. The 11-year study of 40,350 adults, ages 40 to 79, showed that the association of green tea was particularly strong for reduced risk of clot-related strokes. Women seemed to benefit the most, possibly because Japanese men still commonly smoke cigarettes.
That same year, however, the US Food and Drug Administration (FDA) rejected a petition to allow green tea makers to promote cardiovascular benefits on their labels. In nixing the request for a “qualified health claim,” the agency said it reviewed more than 100 studies and found “no credible scientific evidence to support qualified health claims about the consumption of green tea and a reduction of a number of risk factors associated with cardiovascular disease.”
Subsequent evaluations of the evidence have been somewhat more positive. A 2008 meta-analysis of 133 studies of flavonoids and cardiovascular disease, while mostly negative about other antioxidant-rich foods, concluded that green tea reduced LDL (“bad”) cholesterol levels. To achieve clinically significant reductions, based on that analysis, you’d have to drink two to five cups of green tea daily.
In 2009, a review by the Cholesterol Treatment Center at Concord Hospital in New Hampshire concluded that “preliminary evidence supports the possibility that green tea catechins … may lower LDL.” And a British review found that “a positive effect of green tea catechins on vascular function is becoming apparent.”
• Fighting cancer. In 2005, the FDA also rejected a petition to label green tea as protective against breast, prostate, and other cancers. Since then, however, evidence has continued to trickle in. McGill University researchers in Canada have shown in the lab thatEGCG from green tea inhibits the growth of cancer cells. A Japanese study found that women with breast cancer were less likely to suffer a recurrence if they drank at least two cups of green tea daily. An analysis of 22 studies of green tea and lung cancer concluded that consuming two cups daily was associated with an 18-percent lower risk. And the Shanghai Women’s Health Study reported that participants who regularly drank green tea at the start of the study were 37 percent less likely to develop colorectal cancer over six years than those who seldom or never sipped it. Life-long green tea drinkers fared even better, with as much as a 57-percent relative risk reduction.
• Weight control. Helping you lose weight might seem an unlikely benefit of green tea consumption, but several studies have shown that green tea has slimming power. More recently, researchers at the Povident Clinical Research Center in Indiana published results of a study in which 132 participants were split into two groups: Half received a beverage containing 625 mg. of green tea catechins plus 39 mg. of caffeine, while the rest drank a controlled beverage containing only the caffeine. For 12 weeks, participants engaged in at least 180 minutes per week of moderate exercise; calorie intake was kept the same between the two groups. Those in the catechin group tended to lose more weight and showed significantly greater lowering of abdominal fat as well as triglycerides.
A recent review of 15 similar studies concluded that green tea catechins with caffeine modestly reduced body mass index (BMI), body weight, and waist circumference, but not waist-to-hip ratio.
• Protecting against pneumonia. Among the latest proposed green tea benefit is the possibility that its antioxidants might help combat the growth of viruses and other microorganisms. That’s the suggestion of Japanese researchers who recently reported a link between green tea consumption and a reduced risk of dying of pneumonia, at least for women. The study, done at Tohuku University, found that women drinking five or more cups of green tea daily were 47 percent less likely to die of pneumonia, and even those sipping just a cup or so a day were at 41-percent lower risk. The same association was not seen in men, however.
• Keeping cells young. Finally, the notion that green tea might help you live if not forever, at least a little longer might not be so far-fetched. In another recent study, Hong Kong researchers reported that people who drank an average of three cups of tea daily had longer telomeres DNA sequences at the end of chromosomes that shorten with aging than those averaging a quarter-cup daily or less. The cellular difference corresponds to the equivalent of about five years of life, the researchers said, adding: “The antioxidant properties of tea and its constituent nutrients may protect telomeres from oxidative damage in the normal aging process.”
Diane L. McKay, PhD, another scientist at Tufts University, sums it up like this: “Taken altogether, the evidence certainly suggests that incorporating at least a few cups of green tea every day will positively affect your health … It’s not going to cure anything and shouldn’t be consumed as a drug, but it can complement an overall healthy diet.”
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Source: Philippine Star
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