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From Chapter III If you're of Asian descent and have ever had an alcoholic beverage, there's a fifty-fifty chance your heart rate shot up, your temperature climbed, and your face turned bright red. If you're not Asian but you've ever been in a bar frequented by people with an Asian background, chances are you've seen this reaction. It's called Asian flush or, more formally, alcohol flush response. It happens to as many as half of all people of Asian descent, but it's uncommon in just about every other population group. So what's the story? When you consume alcohol, your body detoxifies it and then extracts calories from it. It's a complex process that involves many different enzymes and multiple organs, although most of the process takes place in the liver. First, an enzyme called alcohol dehydrogenase converts the alcohol into another chemical called acetaldehyde; another enzyme—cleverly called acetaldehyde dehydrogenase—converts the acetaldehyde into acetate. And a third enzyme converts that into fat, carbon dioxide, and water. (The calories synthesized from alcohol are generally stored as fat—beer bellies really do come from beer.) Many Asians have a genetic variation (labeled ALDH2*2) that causes them to produce a less powerful form of acetaldehyde dehydrogenase—one that isn't as effective in converting acetaledehyde, that first by-product of alcohol, into acetate. Acetaldehyde is thirty times as toxic as alcohol; even very small amounts can produce nasty reactions. And one of those reactions is the flushing response. That's not all it does, of course. After even one drink by people who have the ALDH2*2 variation, the acetaldehyde buildup causes them to appear drunk; blood rushes to their face, chest, and neck; dizziness and extreme nausea set in—and the drinker is on the road to a nasty hangover. Of course, there's a side benefit to all this—people who have ALDH2*2 are highly resistant to alcoholism. It's just too unpleasant for them to drink! In fact, the resistance to alcoholism is so strong in people with ALDH2*2 that doctors often prescribe alcoholics with a drug called disulfiram, which essentially mirrors the ALDH2*2 effect. Disulfiram (Antabuse) interferes with the body's own supply of the acetaldehyde dehydrogenase enzyme, so anyone who drinks alcohol while taking it ends up with something that looks an awful lot like Asian flush and feels truly awful to boot. So why is the ALDH2*2 variation so common among Asians and virtually nonexistent among Europeans? It's all about clean water. As humans began to settle in cities and towns, they got their first taste of the sanitation and waste management problems that still plague cities today—but without even the possibility of modern plumbing. This made clean water a real challenge, and some theories suggest that different civilizations came up with different solutions. In Europe, they used fermentation—and the resulting alcohol killed microbes, even when, as was often the case, it was mixed with water. On the other side of the world, people purified their water by boiling it and making tea. As a result, there was evolutionary pressure in Europe to have the ability to drink, break down, and detoxify alcohol, while the pressure in Asia was a lot less. The foregoing is excerpted from Survival of the Sickest by Sharon Moalem. All rights reserved. No part of this book may be used or reproduced without written permission from HarperCollins Publishers, 10 East 53rd Street, New York, NY 10022
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