Red wine may be on your Thanksgiving menu, but for some people, even a small glass can result in a headache. Now researchers say they may have figured out why.

In a new study, published in the Scientific Reports journal on Monday, scientists at the University of California, Davis, found the culprit may be a flavanol that occurs naturally in red wines and can interfere with the proper metabolism of alcohol. Flavonols are a group of compounds found in many plants.

The flavanol, called quercetin, is naturally present in grapes and other fruits and vegetables and is considered a healthy antioxidant. However, when metabolized with alcohol, issues can occur. 

"When it gets in your bloodstream, your body converts it to a different form called quercetin glucuronide," wine chemist and corresponding author Andrew Waterhouse, professor emeritus with the UC Davis Department of Viticulture and Enology, said in a news release about the study. "In that form, it blocks the metabolism of alcohol."

The result is a build up of acetaldehyde, an inflammatory toxin that can cause facial flushing, headache and nausea.

Red wine headaches — not to be confused with hangover headaches the day after drinking — do not require excessive amounts of wine, the study notes. In most cases, the headache starts 30 minutes to 3 hours after drinking only one or two glasses.

The amount of quercetin in wines also varies greatly, the researchers note. Factors like the sunlight exposure the grapes receive and how the wine is made can impact the amount present in the final product.

"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,"  Waterhouse said.

So, is there a way to avoid the risk of a headache besides skipping the sipping? That's what scientists are looking to research next.

"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," co-author Morris Levin, professor of neurology and director of the Headache Center at the University of California, San Francisco, said in the release.

That research, a small human clinical trial funded by the Wine Spectator Scholarship Foundation and led by UCSF, intends to determine why some people are more susceptible to these headaches than others and if quercetin or acetaldehyde is the primary target for ameliorating these effects. 

"If our hypothesis pans out, then we will have the tools to start addressing these important questions," Waterhouse said.

In:
• Wine
• alcohol

Sara Moniuszko

Sara Moniuszko is a health and lifestyle reporter at CBSNews.com. Previously, she wrote for USA Today, where she was selected to help launch the newspaper's wellness vertical. She now covers breaking and trending news for CBS News' HealthWatch.

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