If you enjoy a shiraz or Chianti from time to time, you may be familiar with the dreaded "red wine headache." That pain may stem from a compound called quercetin, which disrupts the body's ability to break down alcohol, scientists have discovered.
Quercetin is an antioxidant found in fruit and vegetables, including grape skins, and some people take it as a supplement for its purported health benefits. However, at least in the lab, scientists discovered that it inhibits an enzyme called aldehyde dehydrogenase (ALDH) that's key for metabolizing alcohol in the liver.
Alcohol in the body first gets intercepted by alcohol dehydrogenase (ADH), which breaks it down into a toxic compound called acetaldehyde. ALDH then quickly diffuses that toxin, transforming it into something that can be broken down into water and carbon dioxide. But if what happens in lab dishes also occurs in the body, quercetin may cause acetaldehyde to accumulate. High levels of the toxin in the body can cause flushing, headaches and nausea.
The findings, published Monday (Nov. 20) in the journal Scientific Reports, have yet to be confirmed in humans. But as red wine contains much more quercetin than other alcoholic drinks, the authors say the compound is likely to be the cause of the headaches.
Related: What happens to your body when you stop drinking alcohol?
"We think we are finally on the right track toward explaining this millennia-old mystery," co-senior study author Dr. Morris Levin, a professor of neurology at the University of California, San Francisco, said in a statement.
Scientists have previously proposed many theories to explain the headache that often arrives half an hour after that first sip of merlot, such as preservatives in wine called sulphites being responsible or the inflammatory chemical histamine. But other studies have refuted these ideas. For instance, different levels of histamine in pinot noir had no effect on people's wine tolerance in one study, The New York Times reported.
Now, the authors of the new study think they may have found the answer. "When it [quercetin] gets in your bloodstream, your body converts it to a different form called quercetin glucuronide," study co-author Andrew Waterhouse, a wine chemist at the University of California, Davis, said in the statement. "In that form, it blocks the metabolism of alcohol," he said.
The authors ran specific chemical tests in the lab using samples of quercetin and related compounds, as well as a purified ALDH enzyme. After discovering that quercetin glucuronide inhibits ALDH, the authors estimated that one standard glass of red wine — around 5 ounces (147 milliliters) — would theoretically result in levels of quercetin glucuronide in the blood that could inhibit ALDH by up to 40%. These rough estimates are based on previous studies that examined quercetin levels in people's blood after drinking wine which were factored into the current study's predictions of ALDH inhibition.
The authors plan to test their hypothesis in a small human study where they'll compare people's reactions to red wines with different amounts of quercetin, to see if people are more or less likely to develop headaches.
If proven in humans, the findings could provide opportunities to give customers more choice in the amount of quercetin that ends up in their glass.
Quercetin is produced when grapes are exposed to sunlight, so varieties that are grown in different regions will contain different amounts of the compound. How much the wine touches grape skins during fermentation, as well as how it is clarified and aged, can also influence quercetin levels. To make red wine, wine makers leave the grape skins in during fermentation, whereas they remove the skins when making white wine; that's why red wine contains more quercetin than white.
"It will be potentially very helpful for people who drink red wine to be able to choose wines less likely to cause headaches," Levin told The Guardian. "Also, winemakers may use our findings to reduce quercetin in their wines," he said.
This article is for informational purposes only and is not meant to offer medical advice.
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