Why do Asians get red when they drink alcohol? -- Mechanism behind alcohol flush

Welcome to my first post! This week, let’s talk about why some people get red when they drink alcohol.

Asian flush reaction (Image via Wikipedia)

The reddening reaction after alcohol consumption is known as alcohol flush reaction or Asian flush. The blushing is caused by the dilation of blood vessels in the face or the entire body. But why does this happen?

Alcohol is toxic to your body. When you drink alcohol, your body tries to change it into something non-toxic. Alcohol is first converted into acetaldehyde (toxic) and then into acetic acid (main component of vinegar). This alcohol metabolism mainly happens in the liver, so drinking too much will damage your liver!

The conversion of alcohol into acetaldehyde is mediated by enzymes called alcohol dehydrogenases (ADHs). (Enzymes are proteins that help speed up a reaction.) There is another set of enzymes that breaks down acetaldehydes into acetic acid. These enzymes are called acetaldehyde dehydrogenases (ALDHs).

Alcohol –(mediated by ADHs)–> Acetaldehyde (toxic!) –(mediated by ALDHs)–> Acetic acid

Some people carry mutations in either ADHs or ALDHs or both. Some mutations in ADHs boost their abilities and, as a result, more acetaldehyde is produced. Other mutations in ALDHs cause slower or non-functioning ALDHs, and acetaldehyde builds up in the body. In both cases, the build-up of acetaldehyde results in flushing, nausea, and increased heart rate as your body reacts against the toxic substance.

Structure of ALDH (Image via Wikipedia)

Mutations in ADHs and ALDHs that cause flushing reaction are rarely found in people of European or African origin, while they are frequently found in people of Asian descent. For example, as high as 30% of East Asians are said to have deficient ALDHs.

Is having mutated ADHs and/or ALDHs good? Studies show that people with ADH or ALDH mutations that result in build-up of acetaldehyde are less prone to alcohol abuse, likely because of the uncomfortable side effects. Having said that, it is not always good to have these mutations. Studies have shown that alcoholics with mutations that inactivates ALDHs have higher risks of organ damages, such as upper gastrointestinal (GI) tract cancers.

So it seems that whether you have mutations in ADH/ALDH or not, alcohol should be enjoyed in moderation.

Please leave a comment about this post or suggest topics for the up-coming posts. Also, don’t forget to come back next week for a new post!

References:

The genetics of alcohol metabolism: role of alcohol dehydrogenase and aldehyde dehydrogenase variants.
The evolution and population genetics of the ALDH2 locus: random genetic drift, selection, and low levels of recombination.
Influence of genetic variations of ethanol-metabolizing enzymes on phenotypes of alcohol-related disorders.

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