Why Are Some Ethnicities More Lactose Intolerant? An Evolutionary Perspective

December 21, 2025 •

3 min read

Approximately 65% of the world's population has a reduced ability to digest lactose after infancy, but this varies significantly by ethnic and racial group. The answer to why some ethnicities are more lactose intolerant lies in a fascinating story of human evolution, genetics, and cultural practices that shaped our digestive systems over thousands of years.

Quick Summary

The global disparity in lactose intolerance is primarily due to different evolutionary histories related to dairy consumption. Some populations developed a genetic mutation for lactase persistence, allowing milk digestion into adulthood, while others did not, making lactase nonpersistence the norm. Cultural traditions, like fermenting dairy, also played a crucial adaptive role for many groups.

Key Points

Lactase Nonpersistence is the Norm: For most adult humans globally, the default biological state is to produce less lactase after infancy, leading to lactose intolerance.
Evolutionary Advantage: In populations that began dairy farming, a genetic mutation allowing for continued lactase production (lactase persistence) offered a significant survival advantage.
Diverse Genetic Origins: Lactase persistence evolved independently in different human populations, meaning various genetic mutations grant the same ability.
Cultural Adaptation: Groups with high rates of lactose intolerance often developed cultural food practices, such as fermenting dairy, that naturally reduce lactose content.
Highest Prevalence in East Asia: The highest rates of adult lactose intolerance are found in East Asian populations, who have historically had little to no tradition of consuming fresh milk.
Lowest Prevalence in Northern Europe: Northern European populations have the highest rates of lactase persistence due to a long history of dairy consumption and environmental pressures favoring this trait.
Lactose Content Varies: The tolerability of dairy products depends on their lactose content, with hard cheeses and yogurt being easier to digest than fresh milk.

The Biological Basis of Lactose Intolerance

Lactose intolerance occurs when the small intestine produces insufficient amounts of the enzyme lactase, which is necessary to break down lactose, the sugar found in milk. This inability to break down lactose, known as lactase malabsorption, leads to the undigested sugar passing into the large intestine. Here, bacteria ferment the lactose, producing gas and causing symptoms like bloating, cramping, and diarrhea. For most mammals, lactase production naturally decreases after the weaning period, making lactose nonpersistence the ancestral and default human condition. The continued production of lactase into adulthood, or lactase persistence, is the exception, not the rule.

The Role of Genes and Evolution

The ability to digest lactose into adulthood is a genetic trait, primarily controlled by variants within the MCM6 gene, which regulates the expression of the nearby LCT gene responsible for producing lactase. About 10,000 years ago, as some human populations began domesticating milk-producing animals, a genetic mutation emerged. In these pastoralist societies, being able to digest milk as an adult offered a significant survival advantage, particularly in times of famine or in regions with limited sunlight for vitamin D synthesis. Individuals with this mutation were healthier and more likely to reproduce, leading to the rapid spread of lactase persistence through natural selection. What is remarkable is that this same trait evolved independently multiple times in different regions, an example of convergent evolution.

Global Distribution of Lactose Intolerance by Ethnicity

The uneven historical adoption of dairy farming across the globe is the primary reason for the diverse prevalence of lactose intolerance today. Northern European populations, with a long history of cattle domestication and dependence on milk for nutrition, have the highest rates of lactase persistence. Conversely, many populations whose ancestors did not practice pastoralism, such as those in East Asia, have very low rates of adult lactase production.

Common Lactose Intolerance Prevalence by Ethnic Group:

East Asian Descent (e.g., Chinese, Korean, Japanese): Extremely high, with some estimates suggesting up to 90% are lactose intolerant.
West African Descent: High prevalence, with rates varying significantly but often cited between 65-80%.
Native American Descent: Very high, with some groups approaching 100% prevalence.
Southern European Descent (e.g., Italian, Greek): Higher than Northern Europe, with estimates suggesting 60-80% are lactose intolerant.
Northern European Descent (e.g., Scandinavian, British): Lowest prevalence, with some populations having as few as 5% of adults who are lactose intolerant.
Central Asian Herders: Interesting exception where many populations have adapted culturally (by consuming fermented milk) rather than genetically, despite dairy reliance.

Cultural Adaptations to Low Lactase Levels

For communities where lactase nonpersistence is the norm, cultural practices evolved to allow the consumption of dairy with minimal discomfort. Fermentation is a key process that naturally reduces the lactose content in milk products. This explains why many lactose intolerant individuals can tolerate fermented dairy more easily than fresh milk.


Dairy Product	Typical Lactose Content	Tolerability for LI Individuals
Fresh Milk	High (11-13g per cup)	Poor
Hard Cheeses (e.g., Aged Cheddar, Parmesan)	Very Low (≤ 1g per 1.5oz)	Good
Yogurt (with live cultures)	Low (bacteria consume lactose)	Good
Fermented Products (e.g., Kumis, Kefir)	Low (lactose is broken down)	Good
Ricotta Cheese	High	Poor

Beyond Genetics: The Modern Context

While genetics and ancestry are the most significant factors, other elements can influence an individual's symptoms. Secondary lactose intolerance can occur temporarily due to an intestinal illness or injury, and the severity of symptoms can be influenced by gut microbiota composition. Many people with lactase malabsorption may not experience significant symptoms and can still consume small amounts of dairy, especially with meals. For those who are more sensitive, modern solutions like lactose-free products and lactase enzyme supplements provide ways to enjoy dairy without digestive issues.

Conclusion: A History in Our DNA

The differing rates of lactose intolerance across ethnic groups are a powerful illustration of gene-culture co-evolution. It is a story of natural selection favoring genetic traits that provided a survival advantage within specific environmental and cultural contexts. Lactose intolerance is not a disorder but a snapshot of human adaptation, revealing how the diets and lifestyles of our ancestors continue to shape our biology today. By understanding this, we can move past old assumptions and appreciate the rich tapestry of human diversity, even down to our ability to digest milk. For further reading, the National Institute of Diabetes and Digestive and Kidney Diseases provides detailed information on lactose intolerance.

Frequently Asked Questions

Lactose intolerance is a normal human variation and not a disease. The inability to produce lactase as an adult is the ancestral condition for most humans, while the ability to digest lactose into adulthood is a more recent genetic adaptation.

Lactose intolerance is highly common in people of East Asian descent because their ancestors did not traditionally practice pastoralism or rely on fresh milk for nutrition. Without this selective pressure, the genetic mutation for lactase persistence did not become widespread in these populations.

No, most people with lactose intolerance can consume some amount of lactose without experiencing symptoms. The degree of tolerance varies, and fermented products like yogurt and hard cheeses often cause fewer problems due to their lower lactose content.

No, genetic evidence shows that lactase persistence has evolved independently in several different populations around the world, an example of convergent evolution. This means different genetic mutations resulted in the same outcome: the ability to digest lactose in adulthood.

In cultures where pastoralism was not common, people developed methods like fermenting milk to make products like cheese and yogurt. Fermentation breaks down the lactose, making it digestible for those who are lactase nonpersistent.

Yes, the severity of lactose intolerance varies widely among individuals. Some people can tolerate small amounts of lactose with little to no symptoms, while others have more severe reactions. The amount of lactase an individual produces and their gut bacteria composition can influence this variability.

Yes, secondary lactose intolerance can occur at any age as a result of an injury or illness affecting the small intestine, such as gastroenteritis, celiac disease, or Crohn's disease. This form is often temporary and resolves once the underlying condition is treated.