Metabolism and Bioavailability

Although trans-resveratrol appears to be
well-absorbed by humans when taken orally, its bioavailability is relatively low
due to its rapid metabolism and elimination (7, 8). Resveratrol metabolites are
primarily detected upon oral exposure to trans-resveratrol. When six healthy men
and women took an oral dose of 25 mg of trans-resveratrol, only traces of the
unchanged resveratrol were detected in plasma (blood). Plasma concentrations of
resveratrol and metabolites peaked around 60 minutes later at concentrations
around 2 micromoles/liter (491 micrograms/liter) (7). A study in 12 healthy men
administered an oral dose of 25 mg of trans-resveratrol per 70 kg of body weight
reported that serum concentration of resveratrol and metabolites peaked at 30
minutes after administration. The concentration of total resveratrol
(resveratrol and metabolites) ranged from 416 to 471 micrograms/liter, depending
on whether resveratrol was administered in wine, vegetable juice, or grape juice
(9). Results of another study suggested that the bioavailability of resveratrol
from grape juice, which contains mostly glucosides of resveratrol (piceid), may
be even lower than that of trans-resveratrol (10). A recent study reported that
bioavailability of trans-resveratrol from red wine did not differ when the wine
was consumed with a meal (low- or high-fat) versus on an empty stomach

Information about the bioavailability of resveratrol in
humans is important because much of the basic research on resveratrol has been
conducted in cultured cells exposed to unmetabolized resveratrol at
concentrations that are often 10-100 times greater than peak concentrations
observed in human plasma after oral consumption (12). Although cells that line
the digestive tract are exposed to unmetabolized resveratrol, research in humans
suggests that other tissues are exposed primarily to resveratrol metabolites.
Little is known about the biological activity of resveratrol metabolites, and it
is not known whether some tissues are capable of converting resveratrol
metabolites back to resveratrol (7)

Direct Antioxidant

In the test tube, resveratrol effectively scavenges
(neutralizes) free radicals and other oxidants (13) and inhibits low density
lipoprotein (LDL) oxidation (14, 15). However, there is little evidence that
resveratrol is an important antioxidant in vivo (16). Upon oral consumption of
resveratrol, circulating and intracellular levels of resveratrol in humans are
likely to be much lower than that of other important antioxidants, such as
vitamin C, uric acid, vitamin E, and glutathione. Moreover, the antioxidant activity of
resveratrol metabolites, which comprise most of the circulating resveratrol, may be lower
than that of resveratrol.
It's very important to understand the
difference between results observed from cultures and those produced in vivo.
The data provided as "substantially significant" in support of resveratrol
efficacy is not data from human subjection. Also, as stated, these tests utilize
greatly concentrated percentages not observed in peak human serum levels.
Regardless of the size of the supplements ingested, the human body can/will only
metabolize a small amount of that supplement whilst the excess is disposed of as
waste. So, the overall relevance of the data collected from high concentration
administration is largely inapplicable... especially considering the
inefficiency of resveratrol metabolites (and lacking understanding

A few resources (there are hundreds if you look):

Resveratrol - Wikipedia, the free encyclopedia

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