Green tea is made up of around 30% polyphenols, of these the vast majority are the flavanols known as catechins. The catechins are of four main types: epigallocatechin-3-gallate (EGCG), epigallocatechin (EGC), epicatechin-3-gallate (ECG) and epicatechin (EC). It has been shown that epigallocatechin-3-gallate can be found in quantities as high as 90mg in a standard cup of tea (made from 2.5g of green tea).

Green Tea Flavonol Availability

It is well known that catechins have health benefits, but how much of the flavonols found in green tea are biological available to the consumer? Much research has been carried out on the study of tea catechins.

It has been shown in rats that all four types of catechins have been found in the portal vein, this suggests that the catechins that are found in green tea are absorbed in the intestines. Further work on rats has shown that the most abundant form of catechin found in the plasma are epigallocatechin and epicatechin; this contrasts to that seen in the original green tea where epigallocatechin-3-gallate are by far the most common form of catechins. These results were not the same when the same experiment was carried out with mice; in this case EGCG was the most abundant. These results suggest that the way that the health giving proteins that are found in teas are dependent on species.

Experiments that looked at catechin levels in humans, showed similar results to that found in rats, with EGC being present in the plasma at higher rates than is seen for EGCG tea. After 24 hours of the study is was seen that the extra EGCG levels had disappeared from the plasma whereas that of ECG remained raised.

Where do Tea Catechins work in the Body

Work carried out on rats has looked into the distribution of catechin polyphenols in the body. It was found that.

1. EGC and EC concentrations.
    1. high in the kidney, lung, prostate, large intestine, bladder, esophagus
    2. low in the liver, heart, spleen, thyroid.
2. EGCG concentrations
    1. higher in the esophagus, large intestine
    2. lower in other organs

It can be seen from the above that much work has been carried out into if and how EC, EGC and EGCG tea polyphenols that are consumed by green tea drinkers, are available for the body to use.

References
Kim et al. (2000) Plasma and tissue levels of tea catechins rats and mice during chronic consumption of green tea polyphenols. Nutr Cancer 37: 41 to 48
Cabrera et al. (2006) Beneficial effects of green tea - a review. J. Am. Coll. Nutr. 25: 79 to 99O
kushio et al. (1996) of tea catechins into rat portal vein. Biol Pharm Bull 19: 326 to 329