Flavanol is found naturally in red wines, the suspected culprit flavanol is called quercetin, and it is naturally present in all kinds of fruits and vegetables, including grapes. Levels of the flavanol can vary dramatically in red wine depending on sun exposure and how the wine is made. Quercetin is considered to be a healthy anti-aging antioxidant and it is also available in supplement form. However, when it is metabolized with alcohol, it can be problematic for some people.
“When it gets in your bloodstream, your body converts it to a different form called quercetin glucuronide,” said wine chemist and corresponding author Andrew Waterhouse, professor emeritus with the UC Davis Department of Viticulture and Enology. “In that form, it blocks the metabolism of alcohol.”
People can end up with an acetaldehyde toxin buildup that leads to flushing, headache, and nausea, explains lead author Apramita Devi, a postdoctoral researcher with the UC Davis Department of Viticulture and Enology. “Acetaldehyde is a well-known toxin, irritant, and inflammatory substance,” said Devi. “Researchers know that high levels of acetaldehyde can cause facial flushing, headache, and nausea.”
Interestingly, the medication disulfiram that is prescribed to alcoholics to discourage drinking can also cause the same symptoms because the drugs also cause the toxin to build up when normally an enzyme within the body would break it down. Close to 40% of the East Asian population carry an enzyme that is not very efficient, allowing acetaldehyde to build up.
“We postulate that when susceptible people consume wine with even modest amounts of quercetin, they develop headaches, particularly if they have a preexisting migraine or another primary headache condition,” said co-author Morris Levin, professor of neurology and director of the Headache Center at the University of California, San Francisco. “We think we are finally on the right track toward explaining this millennia-old mystery. The next step is to test it scientifically on people who develop these headaches, so stay tuned.”
“Quercetin is produced by the grapes in response to sunlight,” Waterhouse said. “If you grow grapes with the clusters exposed, such as they do in the Napa Valley for their cabernets, you get much higher levels of quercetin. In some cases, it can be four to five times higher.”
This small clinical trial leaves many unknowns about the causes of red wine headaches, and it is still unclear as to why some people seem to be more susceptible than others. Moving forward the researchers plan to compare red wines with higher levels of quercetin to those with little to test out their theory about red wine headaches on people.
“If our hypothesis pans out, then we will have the tools to start addressing these important questions,” Waterhouse said.
