Party season is also most upon us. A happy time. You’ve splurged on a particularly nice bottle of pinot noir or peppery shiraz to share with friends.

Try not to be too annoyed when one of them sighs and says: “I love red wine. But it doesn’t love me. Yeah, sure, I’ll have a small glass … but I’ll pay for it later with a killer headache. Nobody knows why this happens.”

This will no doubt set off a general discussion about the mystery of red wine and headaches, leaving you – who generously sprung for the top-notch drop – hating them all and otherwise speechless.

Which is a shame because you were hoping to be the centre of attention.

Revenge via knowledge

In the event of this occurring, you can continue to hold court by saying: “Mystery solved. And it’s pretty interesting. A new study from …”

The study, from the University of California, suggests that a type of flavanol found naturally in red wines can, for some people, “interfere with the proper metabolism of alcohol and can lead to a headache”.

What’s a flavanol?

Flavanols are natural compounds commonly found in foods and drinks such as cocoa, grapes, teas and the grapes used to make red wine.

Ironically, they’re actually said to be good for your brain.

As I reported in 2021, a low intake of flavonols is associated with doubling the risk of developing Alzheimer’s disease and related dementias.

The flavanol thought to cause red wine headaches is called quercetin, which has antioxidant and anti-inflammatory effects.

Quercetin is sold as a supplement to reduce swelling, kill cancer cells, control blood sugar, and help prevent heart disease.

None of these benefits have been proven as yet. But they also haven’t been ruled out either.

If quercetin is good for you, why the headaches?

Dr Andrew Waterhouse is a wine chemist and professor emeritus in the department of viticulture and enology at the University of California, Davis. He’s also co-author of the new study.

In a prepared statement he explained that when quercetin gets in your bloodstream, your body converts it to a different form called quercetin glucuronide.

In that form, he said, “it blocks the metabolism of alcohol”.

And that’s where the trouble starts

When you drink alcohol, your body breaks it down into a toxin called acetaldehyde. This is normally broken down by an enzyme. But quercetin glucuronide prevents that from happening.

When acetaldehyde builds up – instead of being metabolised – the toxin causes flushing, headache and nausea.

These are the same symptoms caused by medication prescribed to alcoholics.

Some people – including about 40 per cent of the East Asian population – have an enzyme that doesn’t work very well, allowing acetaldehyde to build up in their system.

Hence the headaches that can start within half an hour of drinking even a small amount of red wine – or creep up on you three hours later.

The new theory

Morris Levin is professor of neurology and director of the Headache Centre at the University of California, San Francisco. He is also a co-author of the new paper.

He said: “We postulate that when susceptible people consume wine with even modest amounts of quercetin, they develop headaches, particularly if they have a pre-existing migraine or another primary headache condition.

“We think we are finally on the right track toward explaining this millennia-old mystery.”

The theory is about to be tested, in a group of people who get these headaches, in a small clinical trial.

Previous theories

According to an explainer from Harvard Medical School, there are three long-standing theories:

Histamine is a compound found in grape skins. There is more of it in red wine than white wine, because “it’s made from the whole grape (including the skin), not just the juice”.

Some people have a shortage of an enzyme that breaks down histamine in the small intestine.

Alcohol also inhibits the enzyme, so the combination may boost histamine levels in the blood, which can dilate blood vessels and cause a headache.

Tannins, also found in grape skins, are implicated in the release of neurotransmitters associated with pain.

Sulfites, a preservative, have long been blamed. But many white wines and other foods also contain sulfites and don’t have an attendant headache.