Lactose Intolerance

Excerpt

Lactose intolerance is a clinical syndrome characterized by gastrointestinal symptoms, such as bloating, abdominal pain, flatulence, nausea, borborygmi, and diarrhea, following the ingestion of lactose-containing food. Although often associated with lactose malabsorption, the 2 terms are not synonymous.

Lactose, a disaccharide and the primary sugar in human breast milk, is hydrolyzed into glucose and galactose by the enzyme lactase, located in the small intestinal border. Galactose is critical for macromolecular synthesis, and human milk is its only natural dietary source. Lactase deficiency, the most common disaccharidase deficiency, is rarely congenital; it typically arises as a secondary process following intestinal injury or as a genetically programmed late-onset decline in enzyme activity.

Lactase activity peaks postnatally and declines thereafter, irrespective of continued lactose intake. This pattern is conserved across most nonhuman mammals. Populations of South American, Asian, and African descent exhibit higher rates of adult-onset lactase deficiency. In contrast, those of northern European and northwestern Indian ancestry more commonly retain lactase activity into adulthood.

Many individuals avoid lactose-containing foods upon symptom onset and diagnosis, often switching to lactose-free products and supplements. This dietary modification, even when based on a presumed rather than confirmed diagnosis, contributes to increased healthcare utilization.