Hello everyone, and welcome back to another blog post! For this post, I decided to explore a bit in the world of biological anthropology, one of the four main branches of anthropology. I typically try to keep my articles primarily centered around the branch of cultural (or social, for my British readers) anthropology, but this topic interested me enough to expand my horizons.
Aldh2 Polymorphism
Colloquially referred to as “Asian Flush”, alcohol flush reaction is a condition in which an individual can develop flushing, swelling, nausea, and a heightened heartbeat, among other symptoms. Such occurs in response to drinking in moderate to heavy quantities in individuals who have Aldh2 Polymorphism. Aldh2 (aldehyde dehydrogenase) is an enzyme encoded by the Aldh2 gene located on chromosome 12. It plays a major role in alcohol metabolism, that is, when the Aldh2 gene’s expression is producing both of its major isozymes. While most White, Black, Latino, and Middle Eastern people have no issues with their Aldh2, 35-50% of East Asian individuals are missing the mitochondrial isozyme. This makes those with the genetic mutation susceptible to alcohol flush reaction, as they are not able to use the isozyme to metabolize the toxic acetaldehyde in alcohol and convert it to the safer compound acetate. The excess of acetaldehyde is what causes the symptoms of flush reaction in the body. Those who have Aldh2 polymorphism carry the rs671 allele on chromosome 12 (also known as Aldh2*2), causing the mutation. (PubMed, Wikipedia)
Image Credit: plos.org
If the load of medical talk was too much for you, luckily, we will now move over to anthropology and examine how this mutation came to impact such a large amount of one population. Many theories exist claiming to answer the mystery of how it came to be; I will address each one and provide my own commentary as to how each could be correct. An article written by Yi-Chyan Chen et al. postulates that the initial genetic mutation spread easily due to the protection it provided from alcoholism as well as the dangers provided by alcohol in early times. This theory says that the mutated gene was favored because of the low rates of excessive alcohol consumption exhibited by its carriers (Chen et al., 2021). Chen’s idea is missing an explanation for why East Asian alcohol fostered natural selection at such a high rate, though, which is why I must continue to the next theory. A more recent study by Giovanni Denna et al. fills in some of the holes in Chen’s theory. Drawing on human evolution more so than Chen, it is here proposed that the Neolithic transition, a major shift in human life from nomadic hunter-gatherer living to a way of life with established settlements and the first agriculture. With rice first being cultivated during this period, the diets of these newly settled homo sapiens underwent a massive change involving the introduction of new pathogens. Denna’s theory suggests that selective pressure stemming from the new pathogens favored ALDH2*2 due to the protection it provided from microorganisms in water or fermented liquids used in alcoholic beverages, taking the focus off of alcohol itself and shifting it to the ingredients that make it up. The evolutionary pressure was reinforced by the popularization of rice-based alcohol, as it is proposed that rice may have been a carrier of pathogens (Peng et al., 2010). A final theory proposes that the selection may have been due to other non-alcohol related effects. Experts have not made a decisive conclusion as to which theory is correct, but the current consensus is that the right answer lies somewhere in the middle ground between all the theories.
Effect on Culture
Though the collection of studies on cultural implications of the ALDH2*2 gene is sparse to say the least, there have been a few interesting effects observed. To state the obvious, the gene deficiency leads to a lower rate of alcohol dependency in the affected population as well as a modified reaction to peer drinking. In cultures like Japan where the majority of people are carriers of the modified gene, drinking traditions have adapted to protect from the flush reaction; alcohol is generally consumed more slowly and in smaller amounts at a time. In some cultures like Japan, an attitude of accommodation towards those with the flush reaction is prevalent as a result of awareness of the flush reaction. This fits with the recurring anthropological theme of biology influencing behavior. Surprisingly, not many other facts on the matter have been revealed by research, as the amount of studies looking into ALDH2 deficiency leaves something to be desired.
Sources Referenced
Chen, Y.-C., Yang, L.-F., Lai, C.-L., & Yin, S.-J. (2021). Acetaldehyde Enhances Alcohol Sensitivity and Protects against Alcoholism: Evidence from Alcohol Metabolism in Subjects with Variant ALDH2*2 Gene Allele. Biomolecules, 11(8), 1183. https://doi.org/10.3390/biom11081183
Shin, M. J., Cho, Y., & Davey Smith, G. (2017). Alcohol Consumption, Aldehyde Dehydrogenase 2 Gene Polymorphisms, and Cardiovascular Health in Korea. Yonsei medical journal, 58(4), 689–696. https://doi.org/10.3349/ymj.2017.58.4.689
Deiana, G., Sun, R., Huang, J., Napolioni, V., & Ciccocioppo, R. (2024). Contribution of infectious diseases to the selection of ADH1B and ALDH2 gene variants in Asian populations. Alcohol, clinical & experimental research, 48(5), 855–866. https://doi.org/10.1111/acer.15288
Wikipedia contributors. (2025, November 4). Alcohol flush reaction. In Wikipedia, The Free Encyclopedia. Retrieved 23:10, December 3, 2025, from https://en.wikipedia.org/w/index.php?title=Alcohol_flush_reaction&oldid=1320340582
Wikipedia contributors. (2025, July 25). ALDH2. In Wikipedia, The Free Encyclopedia. Retrieved 23:12, December 3, 2025, from https://en.wikipedia.org/w/index.php?title=ALDH2&oldid=1302450652
Peng, Y., Shi, H., Qi, Xb. et al. The ADH1B Arg47His polymorphism in East Asian populations and expansion of rice domestication in history. BMC Evol Biol 10, 15 (2010). https://doi.org/10.1186/1471-2148-10-15
O’Shea, T., Thomas, N., Webb, B. T., Dick, D. M., Kendler, K. S., & Chartier, K. G. (2017). ALDH2*2 and peer drinking in East Asian college students. The American journal of drug and alcohol abuse, 43(6), 678–685. https://doi.org/10.1080/00952990.2017.1314489
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