KYOTO, JAPAN. There is now general agreement that oxidation of low-density cholesterol (LDL) is a crucial step in the development of atherosclerosis. There is also considerable evidence that this oxidation can be prevented by some types of alcoholic beverages, notably red wine. Japanese researchers now report that red wine does indeed protect LDL against oxidation, but that white wine, beer and alcohol by itself are ineffective. The researchers carried out two experiments. In the first plasma LDL was incubated for periods varying from 1 to 32 hours with samples of red wine, white wine, beer, alcohol and grape juice in vitro and then allowed to oxidize in the presence of a copper catalyst. The extent of oxidation was followed by measuring the level of thiobarbituric acid reactive substances (TBARS). The results showed that red wine and grape juice are both very effective in preventing oxidation in vitro while white wine, beer, and alcohol itself have no effect. The second experiment involved 20 volunteers aged 20 to 53 years who had blood samples taken one and two hours after ingesting either 300 ml of California red wine, 450 ml of Mosel white wine, 750 ml of Kirin beer or 300 ml of Kagome 100 per cent grape juice. The LDL fraction of the blood was isolated and subjected to copper-catalyzed oxidation. TBARS analyses showed that red wine significantly inhibited oxidation while white wine, beer, alcohol, and grape juice did not. The researchers believe that the active compounds in red wines are the flavonoids especially quercetin. A separate experiment showed that quercetin by itself is highly effective in preventing TBARS formation in incubated LDL plasma. They also suggest that the reason why grape juice is ineffective in vivo even though its flavonoid content is high is that alcohol is needed to facilitate the absorption of flavonoids in the intestines.
Miyagi, Yuko, et al. Inhibition of human low-density lipoprotein oxidation by flavonoids in red wine and grape juice. American Journal of Cardiology, Vol. 80, December 15, 1997, pp. 1627-31