Alcohol tolerance differs among people.This especially gets clear when drinking with people of Asian descent. After a few drinks, they often show a red face and vomiting is imminent. Now don’t make fun of them, while it’s not their fault, it’s their genes.
The liver metabolises alcohol (ethanol) in two steps: in the first step, an enzyme (Alcohol Dehydrogenase; ADH) turns the toxic alcohol into another toxic substance, called acetaldehyde. The second step takes care of the toxic acetaldehyde by turning it into acetate, which is safe for the body. This last step is facilitated by the enzyme Aldehyde Dehydrogenase (ALDH). In people from Asian descent, it’s this particular enzyme they lack
This is caused by a gene variant of the alleles responsible for the enzyme ALDH. Most people carry the ADH1B*1, ADH1C*2 or ALDH2*1 gene that codes for ALDH, but around half of the Asian people carry at least one of the ADH1B*2, ADH1C*1 or ALDH2*2 genes that code for inactive ALDH. Consequently, the acetaldehyde will not be metabolized in acetate and thereby rapidly accumulates in the body, causing redness of the skin, often referred to as “Asian flush”. Besides this, it can cause nausea, headache and even hangovers.
These consequences of the acetaldehyde build-up are the least concerning. Recent studies by Akira Yokoyama and colleagues in Japan showed that the alcohol-related acetaldehyde build-up can even cause esophageal cancer. Yokoyama compared East-Asian people with and without the inactive ALDH-gene. The study showed that the participants with the inactive ALDH-gene are 6-10 times more likely to develop esophageal cancer in comparison with the ones from the active ALDH-gene group. Moreover, compared to non-drinkers, individuals with the inactive ALDH-gene who drink 33 or more drinks (U.S. standard) per week are 89 times more likely to develop alcohol related esophageal cancer,
In summary, around 50% of the Asian people have inactive ALDH, which causes problems when drinking alcohol. These problems include the so-called Asian flush, nausea, headache, hangovers and even esophageal cancer. So next time you have Asian people over, go easy on the bottle, don’t laugh at them when they turn red or vomit, give some advice instead.
This blog was written as an assignment for the course Pharmacology of Cognition, part of the minor Brain and Cognition.