Lactose intolerance is an inability to digest lactose, the main sugar in milk – it is not the same as a food allergy to milk.
- Lactose intolerance is caused by a deficiency of the intestinal enzyme, lactase, that splits lactose into two smaller sugars, glucose and galactose. When lactose moves through the colon without being properly digested, it can cause uncomfortable symptoms such as diarrhea, flatulence (gas), abdominal pain and bloating and even nausea. Lactase deficiency may occur for one of three reasons: congenital, secondary or developmental.
- Congenital causes – lactase deficiency is absent from birth due to a mutation in the gene that is responsible for producing lactase. This is very rare. A person born with lactose intolerance, cannot eat or drink anything with lactose. Some premature babies have temporary lactose intolerance, because they are not yet able to make lactase. After a baby begins to make lactase, the condition goes away.
- Secondary causes – due to diseases that destroy the small intestinal lining along with lactase e.g. celiac sprue. Sometimes the small intestine stops making lactase after a short-term illness (stomach flu) OR as part of a lifelong disease (cystic fibrosis) OR after surgery with removal of a part of the small intestine. Therefore, the problem can be either permanent or temporary.
- Developmental causes – the most common cause of lactase deficiency is a decrease in the amount of lactase that occurs after childhood and persist in adulthood (adult-type hypolactasia). This decrease in lactase is genetically programmed and it varies in the different ethnic groups. It is most common among Asians (more than 90% of adults in some communities); as well as in Africans, South Americans and native Americans. Northern Europeans have a 5% rate of lactose intolerance. There is also a variability in the age at which the lactose intolerance occur.