Myth: Asians can't break down alcohol

02 August 2016

Interview with

Dr Kat Arney, The Naked Scientists

Kat Arney is back with her mythconception and this week she's been busy A glass of Wheat beerresearching in the pub...

Kat - If you're from an Asian background, or if you've ever been out boozing with Asians, you've probably heard of 'Asian glow', and maybe even seen it in action. It's the flushed red face that some people get when they drink alcohol, along with other effects such as a fast heartbeat and a raised temperature after just one or two drinks. This isn't just restricted to Asians, but it is much more common in people from places such as Japan, China and Korea, affecting up to a third of the population there. As a result, many people think that 'Asian glow' is due to a genetic inability to break down alcohol. But in fact, this is a myth - or, at least, the truth is a bit more complicated.

Let's, err, break it down further. When you drink alcohol, whether it's in beer, wine or spirits, it gets broken down in the body, with the products ultimately ending up being used for energy  - or stored as fat (it's not called a beer belly for nothing...). The enzyme that starts the breakdown process is called alcohol dehydrogenase, or ADH. What it does is removes an atom of hydrogen from the chemical structure of ethanol - that's the scientific name for the alcohol we drink. This leaves a related chemical called acetaldehyde - and it's here where things get nasty. Ethanol itself isn't really that bad for your body - apart from the health risks of excessive drunkenness, including accidents and other risky behaviour. But acetaldehyde is relatively toxic, and can have several negative effects on the body, including the unpleasant symptoms of a horrendous hangover the day after, as well as dilating blood vessels in the skin and leading to the famous Asian glow while drinking.

Because of this toxicity, there's another enzyme called aldehyde dehydrogenase, ALDH. Somewhat confusingly, this actually adds an oxygen atom back onto the acetaldehyde, creating acetic acid - the main component of vinegar, and a chemical that our bodies can easily use for making energy. If you imagine the body to be a bit like a funnel, alcohol comes in the top, alcohol dehydrogenase breaks it down into acetaldehyde - which is toxic - and aldehyde dehydrogenase gets rid of that by turning it into acetic acid. If both these enzymes are working properly - and you don't overload the system with too much booze - then you can easily deal with a couple of drinks. But rather than having a problem with the first step of the process - breaking down ethanol - people who experience the Asian glow, or alcohol flush reaction as it's more formally known - have a genetic variation that means their aldehyde dehydrogenase is either ineffective or less efficient. So acetaldehyde quickly builds up, causing the rosy cheeks.

There's another part to the story too. Many Asian people actually have more efficient versions of the first enzyme in the chain - alcohol dehydrogenase - which means that they make acetaldehyde relatively quickly as soon as the first glass of booze hits them. And as well as being embarrassing for some people who suffer from it, this can have serious health effects. The genetic change has been associated with an increased risk of certain types of cancer - particularly cancer of the oesophagus, or foodpipe - due to higher levels of acetaldehyde that can cause damage to cells and DNA. Unfortunately there aren't any really good ways to counteract this, and the best advice is just to cut down on booze.

And finally, there are some bodily effects of alcohol that you can't blame on your genes at all - and that's the bad drunken dancing. Anyone for the Macarena?

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