Lactase is an enzyme located in the small intestines. Its function is to break down lactose, a sugar found in milk and dairy products. It splits lactose into glucose and galactose. In humans, lactase deficiency results in an inability to break down lactose in food, a condition known as lactose intolerance.
In humans, lactase is encoded on chromosome 2. It is mostly found in the small intestine and sparsely in the colon. Infants have high lactase expression. This allows them to digest their mothers' breast milk and survive in the months prior to weaning. As a person grows into adulthood, the body begins producing less lactase. This is a response to the variety of the adult diet and the lack of total dependence on milk.
However, many people suffer from a degree of lactose deficiency that does not allow them to digest whole milk. This is called lactose intolerance. A person who is lactose intolerant experiences diarrhea, cramps and gas. The resultant lack of milk products in such a person's diet leads to weak bones and teeth.
There is no cure for lactose intolerance as there is no way to boost the body's supply of lactase. Persons with lactose intolerance are obliged to seek non-dairy food options that satisfy their dietary requirements of calcium and vitamin D.