The inability to digest lactose, the sugar found in milk, is commonly called lactose intolerance. For most of the global population, however, this is the natural biological state after infancy, more accurately termed lactase non-persistence. This reflects the natural decline of the enzyme responsible for breaking down lactose. Understanding the prevalence of this trait reveals significant population differences, addressing its commonality within the Korean population.
High Prevalence of Lactase Non-Persistence
The vast majority of adults in the Korean population experience lactase non-persistence, the decline in the enzyme that digests lactose. The prevalence of this trait is exceptionally high, often ranging from 80% to over 95% of the population. This makes the inability to fully digest lactose the demographic norm for Korean adults.
This high frequency is typical for East Asian populations, which have some of the lowest rates of lactase persistence globally. In contrast, populations with a long history of dairy farming, such as those in Northern Europe, have high rates of persistence.
Symptoms associated with non-persistence, such as gas, bloating, and discomfort, occur when undigested lactose travels to the large intestine. There, bacteria ferment the sugar, producing uncomfortable byproducts. The degree of symptoms varies significantly among individuals, meaning not everyone with the genetic trait experiences severe discomfort from small amounts of dairy.
The Genetic Explanation for Lactase Decline
The decline in lactose digestion results from the reduced production of the lactase enzyme, which is encoded by the LCT gene. In all mammals, the LCT gene is highly active in infancy to process mother’s milk, but its expression naturally decreases significantly after weaning.
Lactase persistence, the ability to maintain high lactase production into adulthood, is a relatively recent evolutionary adaptation. This trait is controlled by genetic variations in a regulatory region of the MCM6 gene, located near the LCT gene on chromosome 2. These variations prevent the typical “shut-off” of the lactase gene.
In European populations, persistence is primarily associated with a specific single nucleotide polymorphism (SNP) at position C/T-13910. The T variant at this site acts as an enhancer, keeping the LCT gene active in adults. The Korean population, like other East Asian groups, overwhelmingly lacks this specific T variant and other known persistence-conferring mutations.
Studies of human remains from the Joseon period confirm that the genotype of pre-modern Korean people shows a non-persistent genetic profile. This confirms that the high rate of non-persistence is a long-standing genetic characteristic of the population.
Navigating Dairy in Korean Diet and Culture
The high biological prevalence of lactase non-persistence aligns with the historical absence of dairy in traditional Korean cuisine. Dairy farming was not part of the agricultural landscape, and milk products were not staples of the diet, which focused on rice, vegetables, and protein. This traditional pattern naturally accommodated the population’s genetic reality.
Contemporary South Korea has seen a significant increase in dairy consumption due to the Westernization of the diet and new food trends. Products like ice cream, cheese on spicy dishes, and milk in coffee and tea are now widely consumed, especially by younger generations. This modern diet introduces a conflict between the population’s genetic profile and current food choices.
Individuals often manage symptoms by choosing dairy products with reduced lactose content. Fermented dairy, such as yogurt and certain cheeses, contains less lactose because bacteria have already broken down some of the sugar. Consuming small portions of dairy alongside a full meal can also mitigate digestive symptoms.
Despite the high rate of non-persistence, some Koreans consume dairy regularly, often enduring minor discomfort or being unaware of the cause of their symptoms. While milk consumption has increased, the overall intake remains low compared to Western countries, reflecting the continued biological and cultural reality of the population.