29 March 2009

The biochemical basis for "Asian glow"

This is an interesting case of "your body protecting itself from you" (though somewhat inadvertently).

In the body, alcohol (ethanol) is converted by the enzyme alcohol dehydrogenase to acetaldehyde, which is in turn converted by the enzyme aldehyde dehydrogenase (ALDH2) into acetic acid. The intermediate product acetaldehyde is a toxin that contributes to some of the unpleasant reactions associated with hangovers.

Many people of East Asian ancestry have a mutation in the gene encoding alcohol dehydrogenase which makes it particularly effective at producing acetaldehyde, as well as a mutation in the gene encoding ALDH2 that makes it less effective at metabolizing acetaldehyde. Consequently, these people experience the alcohol flush reaction: flushing, nausea, elevated heart rate, and headache almost immediately after drinking alcohol.

Now researchers have found that people with a deficient ALDH2 gene are at elevated risk for squamous cell esophageal cancer, a form of throat cancer, if they drink alcohol. But people with two copies of the deficient ALDH2 are already averse to alcohol! The ones at risk are those with just one copy of the deficient ALDH2, because although they are still at elevated risk of cancer, their alcohol flush reaction is weaker and many of them develop a tolerance against it.

Further reading: New York Times, "Drinkers' Red Face May Signal Cancer Risk", alcohol flush reaction, acetaldehyde and hangovers.

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