Jul 15, 2012
The next time you’re offered a choice between Earl Grey and green tea, you might want to go green—as long as it’s matcha.
Matcha is a stone-ground, powdered high-grade green tea used in Japanese tea ceremonies and certain food products in Japan. Those fortunate enough to drink this elegant tea ingest the entire leaf, not just the steep as with brewed green tea. Young tea leaves are harvested in early May and lightly steamed to prevent fermentation and oxidation. This process accounts for the tea’s unusually beautiful green color.
High-quality matcha tea is like regular green tea on steroids. Studies show that it contains far more of a special form of EGCG called epigallocatechin 3-O-gallate than other green teas. In addition, matcha contains approximately 137 times the amount of EGCG as regular steeped green tea. This is one reason why studies have found that consuming matcha significantly lowers glucose, triglyceride, and total cholesterol levels in the blood and liver and mitigates kidney damage in type 2 diabetics.
Why Go Green?
Matcha is clearly the most healthful type of green tea but in a pinch, any type of green tea will make a beneficial beverage. Although green tea polyphenols have been extensively studied as preventive agents in cardiovascular disease and cancer in lab animals, the effects of green tea consumption in humans have remained murky.
To address this research shortfall, investigators in Japan conducted a large population-based, prospective cohort study initiated in 1994 among 40,530 Japanese adults aged 40 to 79 years without history of stroke, coronary heart disease, or cancer at baseline. Participants lived in the northeastern part of Japan, where green tea is widely consumed. In region, 80 percent of the population drinks green tea and more than half consume 3 or more cups and day. Investigators followed study participants up to 11 years for all-cause mortality and for up to 7 years for cause-specific mortality.
During the 11-year follow-up, 4,209 participants died, and over 7 years of follow-up, 892 participants died of cardiovascular disease and 1,134 participants died of cancer. The researchers determined that green tea consumption was inversely associated with all causes of death and to cardiovascular disease. Compared with participants who drank less than 1 cup/d of green tea, those who consumed 5 or more cups/d had a risk of all-cause mortality and CVD mortality 16 percent lower (during 11 years of follow-up) and 26 percent lower (during 7 years of follow-up), respectively.
The inverse association for green tea consumption was observed in both sexes, however inverse associations of all-cause and CVD mortality were stronger among women. In women, compared with those who consumed less than 1 cup/d of green tea, those who consumed 5 or more cups/d enjoyed a 31 percent lower risk of CVD death. CVD is the leading cause of death among women living in the US.
Green Tea Supports Healthy Endothelial Function
Endothelial dysfunction is a key event in the progression of atherosclerosis, which is the blockage of arteries that increases the risk of heart attack, stroke, and congestive heart failure. Oxidative stress, as occurs with hypertension, high levels of oxidized LDL-cholesterol, diabetes, cigarette smoking, and the aging process itself inactivates nitric oxide, responsible for among other things, the relaxation of the arterial endothelium. Such stresses cause or contribute to endothelial dysfunction.
Drinking green tea can rapidly improve endothelial function. One recent study found that the consumption of green tea rapidly improves flow-mediated dilatation (FMD) of the brachial artery, which represents an estimate of endothelial function. FMD was measured at 30, 90 and 120 minutes after consumption of green tea. Dilatation of the brachial artery as a result of increased blood flow (following a brief period of ischemia of the upper limb) is related to endothelial function and is known to be an independent predictor of cardiovascular risk.
Study results showed that endothelium-dependent brachial artery dilatation increased significantly after drinking green tea, with a peak increase of 3.9 per cent 30 minutes after consumption. Separate FMD tests using caffeine or plain hot water had no significant effect.
Green Tea and Bone Health
There’s freshly brewed evidence that green tea improves bone health—specifically by stimulating bone formation and slowing its breakdown.
Few studies have explored the exact chemicals in tea that might be responsible for this effect. Study investigators exposed a group of cultured bone-forming cells (osteoblasts) to three major green tea components — epigallocatechin (EGC), gallocatechin (GC), and gallocatechin gallate (GCG) — for several days. They found that EGC increased the activity of a key enzyme that promotes bone growth by up to 79 percent. EGC also significantly elevated levels of bone mineralization in the cells. Investigators also discovered that high concentrations of ECG blocked the activity of a type of cell (osteoclast) that breaks down or weakens bones. The green tea components caused no toxic effects to the bone cells, as popular osteoporosis drugs such as bisphosphonates do.
A Stroke Of Luck
If you want to reduce you risk of stroke, it seems tea color doesn’t matter. “By drinking three cups of tea a day, the risk of a stroke was reduced by 21 percent. It didn’t matter if it was green or black tea,” concluded researchers who identified and summarized all human clinical and observational data on tea and stroke. Though no one is certain which compounds in tea are responsible for this effect, researchers speculate that in addition to EGCG found in green tea, the amino acid theanine, found in green and black teas, may be an important bioactive ingredient. EGCG has a poor bioavailability in humans due to but theanine is nearly 100-percent absorbed by the body and it can cross the blood-brain barrier.
Study authors analyzed data from 9 studies involving 4378 fatal and non-fatal strokes among 194,965 individuals. The main outcome was the occurrence of fatal or nonfatal stroke. They found that regardless of their country of origin, individuals consuming > or =3 cups of tea per day enjoyed a 21% lower risk of stroke than those consuming <1 cup per day.
If one drinks three cups a day, the risk falls by 21 percent; follow that with another three cups and the risk drops another 21 percent. Please note that this effect was found in tea made from the plant Camellia sinensis, not from herbal teas.
Investigators concluded that although a randomized clinical trial would be necessary to confirm the effect, results of their meta-analysis suggest that daily consumption of either green or black tea equaling 3 cups per day could prevent the onset of ischemic stroke.
• To boost absorption of EGCG, scientists suggest taking onions (rich in the flavonoid, quercetin) or quercetin supplements with green tea.
• Drink tea no hotter than 70°C (158° F)—cooler is healthier. Drinking very hot tea can increase the risk of cancer of the esophagus. Cancers of the esophagus kill more than 500,000 people worldwide each year.
• Even though Emily Post would frown, jiggle your teabag while steeping to release the maximum amount of green tea polyphenols.
• Can’t find matcha tea in your local supermarket? Try an Asian grocery store or teavana.com or matchasource.com.
• Black tea theaflavins offer powerful disease prevention, so don’t completely eschew conventional English teas.
☆ Disclaimer: This is my informed opinion. I could be wrong. What do you think?
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