Is Resveratrol Bioavailable in Humans?

Resveratrol is one of the major polyphenolic components of red wine. Polyphenols are a group of chemicals that have been shown to have beneficial health effects in humans. However, for polyphenols to be beneficial, they must be absorbed, and there are questions still remaining as to the efficiency of the absorption of many polyphenolic substances. Polyphenol absorption is complicated further by red wine because the chemical composition of the wine is not fully understood and each bottle may have quite different polyphenolic profiles. Research using isolated polyphenols can provide a clearer picture of their absorption rates and patterns, but are not realistic because polyphenols are not found isolated in foods. That being said, they are a useful model to determine the general absorption characteristics of polyphenols such as resveratrol. Human studies suggest that resveratrol is bioavailable in humans, but extensive metabolism of the parent compounds in wine may occur rapidly prior and following absorption.

Red wine consumption under various conditions has been investigated by researchers. For example, in one study1 subjects consumed red wine with a standard mixed meal, a high fat meal, a low fat meal and under fasting conditions. The plasma of the subjects was then analysed using analytical chemistry. The results of the study showed that resveratrol, the main stilbene polyphenolic compound in red wine, was found in its unmetabolised free form in plasma for only 30 minutes following wine consumption. After this time, the glucuronide metabolite of resveratrol became the dominant resveratrol form in the plasma. There was also no effects of meal content on the bioavailability of the resveratrol form. In addition, there was considerable variability in the metabolism of resveratrol between subjects. These data support other studies that show that polyphenols are extensively and rapidly metabolised to phase 2 conjugates in humans. The biological effects of phase 2 conjugates are however controversial.

Therefore consumption of red wine in its whole form forms confirms the results of studies using isolated resveratrol. Resveratrol, once ingested passes to the enterocytes of the small intestine, where it is absorbed. Here much of the resveratrol is metabolised to phase 2 conjugates and many of these are effluxed back to the gut lumen, where they are further metabolised by the microflora in the large intestine. Any resveratrol in its free aglycone form that is absorbed to the circulation is metabolised rapidly during first pass metabolism in the liver, resulting in its rapid disappearance from circulation. Most of the cell culture experiments that investigate the effects of polyphenols are performed with the free form of the compound. That the polyphenols are extensively metabolised and present largely in the glucuronide or sulfate form in plasma suggests that their bioactive properties are far more complex that may have been considered. This is an ongoing area of research and so little is understood about tissue effects in vivo.

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1Vitaglione, P., Sforza, S., Galaverna, G., Ghidini, C., Caporaso, N., Vescovi, P. P., Fogliano, V. and Marchelli, R. 2005. Bioavailability of trans-resveratrol from red wine in humans. Molecular Nutrition and Food Research. 49: 495-504

About Robert Barrington

Robert Barrington is a writer, nutritionist, lecturer and philosopher.
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