Teacup1980 wrote: if you infuse 4g of tea leaves -->4g x 15% x 15% = 90mg
Nah, I really don't think it is as simple as that. You are underestimating the power of fresh high quality leaf along with other variables.
Most of the tea studies you see floating around usually don't get into the specifics of leaf quality, harvest season,brewing parameters, specific varietal etc etc. There's a lot to speculate on from the current science out there. Then you take into account the effect multiple boiling infusions has on a single pot of leaf and its gets even more inconclusive.
Teacup1980 wrote:I think the "tea containing 690mg catechins" is not technically tea.
A definite possibility. It could have been tea leaves brewed with ethanol to enhance extraction. I have seen a few studies like this.