- Lactase (lactase-phlorizin hydrolase) is an essential enzyme in the human digestive system that breaks down lactose, the primary sugar found in milk and dairy products, into its component monosaccharides: glucose and galactose. This enzyme belongs to the β-galactosidase family and is produced by cells lining the small intestine, with the highest concentrations found in the jejunum. Lactase functions optimally at pH 6-8 and is anchored to the intestinal membrane as a transmembrane glycoprotein.
- The clinical significance of lactase primarily relates to its deficiency, which leads to lactose intolerance. There are three main types of lactase deficiency: primary (genetic decrease in lactase production with age), secondary (temporary loss due to intestinal damage), and congenital (rare genetic condition present from birth). When individuals with lactase deficiency consume dairy products, they typically experience symptoms such as bloating, gas, diarrhea, and abdominal pain, as the undigested lactose is fermented by gut bacteria.
- The genetics and evolution of lactase production are particularly interesting from an anthropological perspective. Lactase persistence, the continued production of lactase into adulthood, evolved independently in different populations, particularly those with a history of dairy farming. This trait is regulated by genetic elements near the lactase gene (LCT), and several different mutations can cause lactase persistence. Approximately 35% of humans maintain lactase production into adulthood, though this percentage varies significantly among different ethnic groups.
- Clinical management of lactose intolerance typically involves several strategies. These include dietary modification to reduce lactose intake, use of lactase enzyme supplements before consuming dairy products, consumption of lactose-reduced dairy products, and proper timing of dairy consumption. Some individuals may also benefit from probiotics that can help break down lactose. The severity of lactose intolerance varies among individuals, and many people can tolerate small amounts of dairy products without significant symptoms.
- Diagnosis of lactase deficiency can be accomplished through several methods. The most common are the lactose tolerance test and the hydrogen breath test, which measure the body’s ability to digest lactose. Genetic testing can identify mutations associated with lactase persistence or non-persistence. In rare cases, a small intestinal biopsy may be performed to directly measure lactase activity, though this is typically unnecessary for diagnosis. Often, a trial elimination of dairy products, followed by controlled reintroduction, can help confirm the diagnosis and determine an individual’s tolerance threshold.
- Research continues into the molecular mechanisms of lactase expression and regulation, which may lead to new therapeutic approaches for managing lactose intolerance. Understanding lactase biology has important implications for both clinical medicine and the food industry, driving the development of lactose-free products and enzyme supplements to help those with lactase deficiency enjoy dairy products without adverse effects.
