Lactase deficiency (lactose intolerance) is more common in Asian, Native American, Mediterranean, and some African populations than in people with Northern or Western European ancestry primarily due to genetic and evolutionary factors.
Explanation
- Genetic basis: Lactase persistence, the ability to digest lactose into adulthood, is controlled by genetic mutations, particularly in the regulatory region of the MCM6 gene that controls expression of the LCT gene responsible for lactase production. Most humans originally had lactase nonpersistence, meaning lactase production declines after weaning, leading to lactose intolerance
- Evolutionary adaptation: Lactase persistence evolved independently in several populations as an adaptation to the domestication of dairy animals about 10,000 years ago. This mutation provided a selective advantage in populations that relied on dairy farming, mainly in Northern and Western Europe, where nearly 95% of adults are lactose tolerant today
- Population differences: In contrast, many Asian, Native American, Mediterranean (e.g., Greeks, Italians), and African populations historically did not rely as heavily or as early on dairy farming, so lactase persistence mutations were less common or absent. Consequently, lactase deficiency is highly prevalent in these groups — for example, 70-100% in East Asians, high rates in West Africans, Arabs, Jews, and Mediterranean peoples
- Cultural dietary adaptations: Some traditional societies with high lactose intolerance adapted by consuming fermented dairy products with reduced lactose content, mitigating symptoms despite lactase deficiency
In summary, the variation in lactase deficiency prevalence is explained by the genetic evolution of lactase persistence in populations with a history of dairy farming, which occurred predominantly in Northern and Western Europe, while other populations retained the ancestral lactase nonpersistence trait due to different dietary histories and selective pressures
