Lactase

Lactase is a disaccharidase enzyme that catalyzes the hydrolysis of lactose, the sugar found in milk, into its component monosaccharides, glucose and galactose. In humans, lactase is produced by enterocytes of the small intestine, where it is located on the brush border. The enzyme is commonly referred to as lactase-phlorizin hydrolase (LPH) and is produced as a single polypeptide that is cleaved into subunits with lactase and phlorizin hydrolase activities. Its activity is optimized in the milieu of the small intestine, allowing efficient digestion of dairy lactose.

Genetic variation largely determines adult lactase activity. Many mammals, including most humans, reduce lactase production after weaning, leading to lactase non-persistence and potential lactose intolerance. In contrast, some human populations retain high lactase expression into adulthood, a trait known as lactase persistence. The persistence is associated with regulatory genetic variants upstream of the LCT gene, such as those in the LCT/MCM6 region, which help maintain transcription of the enzyme. The distribution of lactase persistence varies geographically and is linked to historical dairy consumption.

Clinical significance includes lactose intolerance, caused by lactase deficiency. Symptoms after dairy ingestion include bloating, abdominal pain, gas, and diarrhea. Primary lactose intolerance stems from age-related decline in lactase, while secondary lactose intolerance can result from intestinal injury or disease. Diagnosis methods include hydrogen breath tests, lactose tolerance tests, and genetic testing for lactase persistence variants.

Management focuses on dietary modification and enzyme supplementation. Individuals may limit or avoid lactose-containing foods, choose lactose-free products, or use over-the-counter lactase enzyme supplements. Lactase is also widely used in the dairy industry to produce lactose-free milk and other dairy ingredients.