Lactase is normally produced in the small intestine where it breaks lactose down into a form that can be absorbed by the blood. A lack of lactase can cause uncomfortable symptoms for some people. Those who do exhibit the symptoms are said to be lactose intolerant. Thirty to 50 million Americans are lactose intolerant. Ninety percent of Asian-Americans are lactose intolerant.
Lactose intolerance is least common among people with a northern European heritage.
Digestive diseases or injuries to the small intestine can reduce the amount of enzymes produced, and some children are unable to produce lactase from birth. However, most cases of lactose intolerance develop over a period of many years. The following are the most common symptoms for lactose intolerance, however, each individual may experience symptoms differently. The severity of symptoms varies depending on the amount of lactose consumed and the amount each individual can tolerate. The symptoms of lactose intolerance may resemble other conditions or medical problems.