Lactose intolerance is an inherited, or acquired, inability to digest lactose, the sugar found in milk, due to a lack of the enzyme lactase. There is a marked racial variation, with northern Europeans having an incidence of only 2% lactose intolerance, while African Negroes have an incidence of up to 98% in Zambia, and more than 50% of Asians having lactose intolerance. The ability to digest lactose is present in all races equally at birth, but the enzyme lactase fails to be produced by about three years of age in those who have a genetic tendency to lactose intolerance.
It may temporarily follow an episode of gastroenteritis, or may gradually develop from four or five years of age and last lifelong.
The symptoms include bloating, diarrhoea, nausea, excess wind and belly cramps. It is controlled by removing dairy products from the diet.
The severity varies, and some patients may tolerate some dairy products, while others cannot eat any at all. High lactose dairy products include full cream milk, yoghurt and custard; moderate levels of lactose are found in ice cream, soft cheeses (eg. cottage cheese, ricotta) and cream; while hard cheeses (eg. cheddar, parmesan) and ripened cheeses (eg. brie, camembert, edam, Swiss) are low in lactose.
Margarine and soy products can be used as dairy substitutes by patients who are lactose intolerant.