Lactase deficiency and lactose malabsorption. A review.

The results of previous investigations of lactase deficiency and lactose malabsorption are reviewed. It showed that lactase activity and its decline in animals and humans is controlled genetically, but also that its phenotypic expression as lactose malabsorption is influenced by nongenetic factors: adaptation, biological (circadian) rhythmicity, hormones, gastrointestinal functions, and nutritional components can alter the response to lactose intake.