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Green tea antioxidants more bioavailable than thought?

By Stephen Daniells , 22-Jan-2010

The bioavailability of antioxidant catechins from green tea may be more than previously thought, says a new study from Italy.

By taking into account metabolites called colonic ring fission metabolites the bioavailability of green tea flavan-3-ol and related compounds is almost 40 per cent, a lot higher than the 4 per cent reported earlier, according to findings published in Nutrition.

“It must be noted that the great majority of the excreted flavan-3-ol catabolites are microbial ring fission valerolactones, raising the bioavailability figure to almost 40 per cent, and that it would be much more feasible for these compounds to be bioactive, based on their high concentration in biological fluids,” wrote the researchers, led by Furio Brighenti from the Department of Public Health at the University of Parma.

“Unfortunately, the literature lacks reports on their biological effects and the fact that they are present in conjugated forms makes even more difficult their investigation as putative protective agents,” they added.

The news may well be welcomed by the burgeoning tea extract market, already valued at a around $44m (€29.7m), according to recent report from Frost & Sullivan. The market is expected to grow by more than 13 per cent over the next seven years.

The F&S analysts state that science is the reason for the ingredient's growing popularity, and that it is generally accepted that green tea has a beneficial role in reducing Alzheimer's, certain cancers, cardiovascular and oral health.

Study details

By combining high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS), the researchers measured all the known and some unknown metabolites of green tea following ingestion of a ready-to-drink green tea containing about 400 micromoles of flavan-3-ols by 20 healthy humans.

Thirty-nine compounds were identified, with epigallocatechin-3-gallate the only un-metabolized compound found in the blood, and in the highest amounts compared with epigallocatechin and epicatechin conjugates, they said.

The other compounds were metabolized by bacteria in the colon. “It is interesting to notice the great variability in urinary excretion of colonic metabolites among participants, probably related to differences in their own colonic microflora,” they said.

“This study demonstrates that green tea catechins are more bioavailable than previously observed when colonic ring fission metabolites are taken into consideration,” wrote the researchers.

“Regular consumption of ready-to-drink green tea containing flavan-3-ols allows a non-marginal exposure of the human body to these catabolites, somehow justifying the numerous beneficial actions described as linked to green tea intake,” they concluded.

Source: Nutrition
published online ahead of print, doi: 10.1016/j.nut.2009.09.021
“Bioavailability and catabolism of green tea flavan-3-ols in humans”
Authors: D. Del Rio, L. Calani, C. Cordero, S. Salvatore, N. Pellegrini, F. Brighenti

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