June 12, 2024

Causes of Lactose Intolerance


Lactose intolerance is a common digestive disorder affecting millions of people worldwide. It occurs when the body cannot adequately digest lactose, a sugar found in milk and dairy products, due to a deficiency of lactase, an enzyme produced in the small intestine. This blog delves into the various causes of lactose intolerance, including genetic factors, secondary conditions, developmental changes, and environmental influences, providing a comprehensive understanding of this condition.

Overview of Lactose Intolerance Causes

Lactose intolerance can be categorized into different types based on its underlying causes. Understanding these causes is crucial for effective management and treatment. The primary types of lactose intolerance are:

  1. Primary Lactose Intolerance (Lactase Non-Persistence)
  2. Secondary Lactose Intolerance
  3. Developmental Lactose Intolerance
  4. Congenital Lactase Deficiency

Each type has distinct causes and mechanisms, which we will explore in detail.

Genetic Causes

Explanation of Lactase Non-PersistencePrimary lactose intolerance, also known as lactase non-persistence, is the most common form. It is genetically determined and results from a gradual decrease in lactase production after weaning. Most mammals, including humans, produce high levels of lactase during infancy to digest their mother's milk. However, for many individuals, lactase production significantly decreases as they age, leading to lactose intolerance.

Inheritance Patterns and Genetic TestingLactase non-persistence follows an autosomal recessive inheritance pattern. This means that an individual needs to inherit two copies of the gene associated with lactase non-persistence (one from each parent) to exhibit symptoms. Genetic testing can identify specific variants in the LCT gene, which codes for the lactase enzyme, providing a definitive diagnosis. These tests can be particularly useful for understanding familial patterns and predicting the likelihood of developing lactose intolerance.

Secondary Lactose Intolerance

Secondary lactose intolerance occurs when an underlying condition affects the small intestine, leading to a temporary or permanent reduction in lactase production. Unlike primary lactose intolerance, which is genetically determined, secondary lactose intolerance results from damage to the intestinal lining. Common causes include:

Intestinal Diseases

  • Celiac Disease: An autoimmune disorder where ingestion of gluten leads to damage in the small intestine, impairing lactase production.
  • Crohn's Disease: A type of inflammatory bowel disease (IBD) that causes inflammation of the digestive tract, potentially affecting the small intestine's ability to produce lactase.
  • Ulcerative Colitis: Another form of IBD that primarily affects the colon but can also cause secondary lactose intolerance.


  • Gastroenteritis: Viral or bacterial infections causing inflammation of the stomach and intestines can temporarily reduce lactase production.
  • Parasitic Infections: Certain parasites, like Giardia lamblia, can damage the intestinal lining, leading to lactose malabsorption.


  • Surgery: Surgical procedures involving the small intestine can damage the cells that produce lactase, resulting in secondary lactose intolerance.
  • Radiation Therapy: Radiation treatment for abdominal cancers can harm the intestinal lining, decreasing lactase production.

Developmental and Congenital Causes

Developmental Decline in Lactase ProductionIn some cases, lactase production decreases naturally with age, even in the absence of genetic predisposition. This decline typically begins after weaning and can continue into adulthood. While this developmental decline is normal in many populations, it varies widely based on genetic background and dietary habits.

Congenital Lactase DeficiencyCongenital lactase deficiency is a rare genetic disorder present from birth, resulting in little to no lactase production. This condition is inherited in an autosomal recessive manner, meaning both parents must carry and pass on the defective gene. Infants with this disorder experience severe diarrhea and malnutrition if they consume lactose-containing foods. Early diagnosis and management with a lactose-free diet are crucial for their health and development.

Environmental and Dietary Factors

Impact of Diet and Environmental ChangesEnvironmental and dietary factors can influence the severity and onset of lactose intolerance. While genetics play a significant role, the environment also affects lactase persistence and lactose intolerance.

  • Dietary Habits: Populations with historically low dairy consumption tend to have higher rates of lactose intolerance. For example, many East Asian and African populations have high prevalence rates due to traditional diets that include little to no dairy.
  • Dietary Changes: Sudden increases in dairy consumption can unmask latent lactose intolerance in individuals who previously consumed low-lactose diets. Conversely, gradual introduction of dairy products can sometimes increase tolerance by promoting lactase production through adaptation of the gut microbiota.
  • Environmental Changes: Changes in living conditions, such as migration from a dairy-consuming region to a non-dairy-consuming one, can influence the prevalence of lactose intolerance. Additionally, socioeconomic factors and access to lactose-free alternatives can impact how individuals manage their condition.


Lactose intolerance is a complex condition with multiple causes, ranging from genetic factors and secondary conditions to developmental changes and environmental influences. Understanding the diverse causes of lactose intolerance is essential for effective diagnosis, management, and treatment. By recognizing the underlying mechanisms, individuals and healthcare providers can better address the challenges associated with lactose intolerance, improving digestive health and quality of life.

In summary, lactose intolerance stems from a variety of causes, including genetic lactase non-persistence, secondary conditions such as intestinal diseases and infections, developmental declines in lactase production, congenital lactase deficiency, and environmental and dietary factors. Addressing these causes through proper diagnosis, dietary management, and awareness can significantly enhance the well-being of those affected by this common digestive disorder.

Related Posts