Red wine is a complex mixture of a number of polyphenolic substance, that may explain some of its beneficial health effects. Of the polyphenolics present in red wine, flavonoids represent one group that have shown beneficial effects against cardiovascular disease and cancer. The flavon-3-ol group of flavonoids are present in red wine in relatively high concentrations and individual members include catechin and epicatechin, as well as complex flavan-3-ol oligomers called procyanidins. The exact quantity of flavan-3-ols in red wine varies between the variety, but generally concentrations of catechin equivalents vary from between 4.0 and 5.4 µmol/mL1. Research suggests that catechins are bioavailable in humans, but only around 12.5% of the absorbed catechin is detected in the plasma unmetabolised. Urine analysis shows that 60% of the catechin is metabolised and that 3’-O-methylcatechin and glucuronide and sulfate conjugates are formed.
Researchers2 have investigated the absorption of catechin in five male and four female volunteers. Subjects ingested 120mL of red wine or non-alcoholic red wine on different days, with each sample standardised to contain 35 mg of catechin. Blood samples of the subjects were taken an analysed for catechin and 3’-O-methylcatechin and its sulphated and glucuronidated metabolites. At baseline before consumption of red wine, catechin and all conjugates were less that 2 nmol/L. One hour post consumption, the levels of all catechin and catechin conjugates had risen to 91 nmol/L and 81 nmol/L in red wine and non-alcoholic red wine, respectively. Of the catechin present in the plasma sample at 1 hour, <2% of the catechin and 3’-O-methylcatechin were unconjugated. Catechin was present as sulfate and sulfo-glucuronide conjugates, but 3’-O-methylcatechin was primarily glucuronidated.
These results suggest that catechin is absorbed in humans and that during the process, there is an extensively metabolised to produce a variety of conjugate forms. This supports previous and subsequent work that shows that flavonoids are present in humans plasma and urine mainly as conjugates and that the parent flavonoids are always present in low concentrations. This would tend to suggest that the protective effects of flavonoids are due to their metabolised forms. The total flavonoid content of the plasma following red wine consumption is likely to be higher than reported here, due to the presence of other flavonoids, notably flavonols such as quercetin, in the wine. Further, it would appear that the presence of ethanol does not influence the metabolism and absorption of catechins as both normal red wine and the non-alcoholic equivalent produced similar plasma levels of flavon-3-ols.
RdB
