Green tea, the infusion prepared from leaves of the Camellia sinensis plant, is proving to be an exciting “functional food” for addition to a comprehensive program of heart health and atherosclerotic plaque control. Anti-inflammatory and anti-oxidative properties have gained increasing attention, as well as thermogenic visceral fat-reducing effects.
Green tea can also be a source of great pleasure. Ever since its discovery by Chinese emperor Shen Nung in 2700 BC who, according to legend, was sipping hot boiled water in his garden when the leaf from a tea bush fell into his cup yielding a fragrant and delicious infusion, tea has fascinated, soothed, and provided pleasure for the nearly 50 centuries since. All manner of health benefits have been attributed to tea, from enhanced virility to a cure for cancer, beliefs that likely originate with the mood-lifting methylxanthines (theobromine, caffeine, and trace quantities of theophylline) and theanine. The simple perceived and immediate benefits of tea are now yielding to an appreciation of the greater potential health benefits of tea flavonoids, components that do not yield perceptible effects but may provide substantial health benefits with long-term consumption.
Can you say “catechin”?
Like other plants, the leaves of Camellia sinensis contain chlorophyll, vitamins, minerals, oils, and other components. They are also unusually rich in flavonoids, especially a unique class of flavonoids called catechins. Approximately 30-36% of the dry weight of tea leaves are catechins (Manning 2003).
More than blueberries, pomegranates, or red wine, green tea packs a considerable wealth of healthy flavonoids. Per 100 gram serving, for instance, red wine typically provides 27.77 mg total flavonoids (mostly anthocyanins, catechins, and quercetin), blueberries provide 224.29 mg flavonoids (also mostly anthocyanins, catechins, and quercetin), and 100 g brewed green tea typically provides 133.34 mg flavonoids, nearly all catechins, 58% of which (77.81 mg) are epigallocatechin-3-gallate. This means that an 8 oz (226.8 grams) serving of brewed green tea provides an impressive 302.4 mg total flavonoids (USDA Flavonoid Database 2007). Decaffeinated teas have less than half the catechin content of caffeinated teas due to catechins lost during the caffeine extraction process (Henning 2003).
The presumed active ingredients for health effects in green tea include the catechins epicatechin, epicatechin-3-gallate, epigallocatechin, and epigallocatechin-3-gallate (EGCG). Catechins comprise 30-36% of the dry weight of green tea, of which epigallocatechin-3-gallate is the most plentiful, comprising approximately 58% of all flavonoids in green tea (Lin 2000).
From USDA Flavonoid Database 2007
After ingestion, catechin blood levels peak at 30-60 minutes and drift back down to baseline levels after four hours with a dose of 455 mg (Hsu 2007). Higher doses of up to 1600 mg peak at 1.3-2.2 hours after ingestion (Ullmann 2003). Analyses have demonstrated that bioavailability, i.e., the quantity of active metabolites available at the blood level, increases 60% with EGCG intake of 800 mg or more per day, likely due to exceeding the body's capacity to metabolize EGCG to a less active (glucoronidated) form (Chow 2003).
Flavonoids from all sources, tea and otherwise, experience limited absorption, but tea catechins are somewhat better absorbed than most others with up to 40% of ingested quantity measurable in the bloodstream (Del Rio 2010; Roowi 2010).
Green tea also contains caffeine, approximately 20-30 mg per 8 oz, or about 25% that of coffee. White teas, teas prepared from an immature tea plant but containing similar catechin composition to green tea, is naturally lower in caffeine.
Cardiovascular benefits of green tea
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