What causes lactose intolerance and how common is it?
Lactose intolerance occurs in individuals who lack or have low levels of the enzyme lactase, which is needed to digest the sugar lactose (found in milk) to its constituent sugars (glucose and galactose) in readiness for absorption in the small intestine. It is a condition seen in older children and adults. In the absence of lactase, undigested lactose passes into the large intestine causing the characteristic symptoms of diarrhoea, wind, and general discomfort. In about 70% of the world’s population, a reduction in lactase production after early childhood is the norm. When milk is consumed, symptoms are typically experienced to varying degrees in people of Asian, African, Jewish, and Hispanic descent. Nevertheless, the majority of affected individuals can still tolerate moderate amounts of dairy products (such as a glass of milk), particularly if these are consumed as part of a meal. Complete avoidance is rarely necessary, as most people still produce some lactase enzyme. Hard cheese c
