An inability to digest lactose, the natural sugar found in milk
A person who is lactose intolerant is unable to digest lactose, a natural sugar found in milk and dairy products. As a result, the lactose remains undigested in the intestines. In an affected person, even small amounts of lactose can cause abdominal pain and diarrhoea. Lactose intolerance usually develops in adolescence or adulthood, and only rarely affects babies. Worldwide, about 8 in 10 people of African, Native American, Asian, and Jewish origin develop an inability to digest lactose in the diet.
Normally, the enzyme lactase breaks down lactose in the intestines to form the sugars glucose and galactose, which are easily absorbed through the intestinal wall. If this enzyme is absent, the unabsorbed lactose ferments in the large intestine and produces painful symptoms. Although high levels of lactase are present at birth, in many ethnic groups the levels can drop with increasing age, becoming very low by adolescence so that lactose can no longer be digested.
In children and babies, lactose intolerance sometimes develops temporarily following an attack of gastroenteritis that causes short-term damage to the lining of the intestine.
The symptoms of lactose intolerance usually develop a few hours after eating or drinking products containing milk. They may include the following:
Abdominal bloating and cramping.
The severity of the symptoms depends on the degree of lactase deficiency. One person may experience symptoms only after drinking several glasses of milk, but another may feel discomfort after consuming only a small amount of a dairy product.
Your doctor may be able to diagnose lactose intolerance from your symptoms. He or she will probably ask you to keep a diary of all the foods you eat and the symptoms that occur. You may then have a specialized test to confirm lactose intolerance. Alternatively, your doctor may ask you to eliminate all dairy products from your diet for a few days. If your symptoms improve but return when dairy products are reintroduced into your diet, the diagnosis of lactose intolerance is confirmed.
Lactose intolerance is usually permanent in adults. However, the symptoms can be completely relieved by eliminating lactose from the diet. In order to achieve this aim, it is important to remember that you should avoid all dairy products, such as milk, yogurt, cheese, cream, and butter. Milk products that have been specially treated by having the lactose broken down are available over the counter. In addition, your doctor may suggest that you take lactase supplements in the form of liquid or capsules. In babies whose lactose intolerance is caused by gastroenteritis, the condition usually improves over several days and milk can be continued during this period.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.