Digestive Diseases: Lactose Intolerance

Lactose intolerance is the inability to digest lactose, the sugar primarily found in milk and dairy products. It is caused by a shortage in the body of lactase, an enzyme produced by the small intestine, which is needed to digest lactose. While lactose intolerance is not dangerous, its symptoms can be distressing.

What Are the Symptoms of Lactose Intolerance?

Symptoms include:

• Nausea
• Cramps
• Painful gas
• Bloating
• Diarrhea

Symptoms tend to develop 30 minutes to two hours after consuming milk or dairy products. The severity of symptoms varies, depending on the amount of lactose an individual person can tolerate. Some people may be sensitive to extremely small amounts of lactose-containing foods while others can eat larger amounts before they notice symptoms.

What Foods Contain Lactose?

The most common foods that are high in lactose include dairy products such as milk, ice cream and cheese. Lactose is also added to some foods, such as bread and baked goods, cereals, salad dressings, candies and snacks.

Foods that contain whey, curds, milk by-products, dry milk solids and nonfat dry milk also contain lactose.

Lactose is also present in about 20% of prescription medications, such as birth control pills (oral contraceptives), and about 6% of over-the-counter medications, such as some tablets for stomach acid and gas.

Who Gets Lactose Intolerance?

Lactose intolerance is extremely common. It is estimated that 30 to 50 million Americans have some degree of lactose intolerance. Certain racial and ethnic populations are more affected than others, including 75% of African Americans, Jews, Mexicans and Native Americans, and 90% of Asians.

What Causes Lactose Intolerance?

For most people, lactose intolerance develops naturally as they grow older. The small intestine begins to produce less lactase in everyone after age two. Certain digestive diseases such as Crohn's disease, celiac disease (a digestive disease that damages the small intestine and interferes with absorption of nutrients from food) and injuries to the small intestine can also reduce the amount of lactase available to process lactose properly.

How Is Lactose Intolerance Diagnosed?

Usually lactose intolerance is diagnosed based on symptoms and relief of those symptoms when avoiding dairy products.

However, health care providers can perform certain tests to help confirm the diagnosis. Many doctors will ask patients who suspect they have lactose intolerance to avoid milk and dairy products for one or two weeks to see if their symptoms subside, and will then confirm the diagnosis with the hydrogen breath test, a lactose intolerance test or a stool test.

Milk Challenge Test:A milk challenge is a simple way of diagnosing lactose intolerance. A person fasts overnight and then drinks a glass of milk in the morning. Nothing further is eaten or drunk for three to five hours. If a person is lactose intolerant, the milk should produce symptoms within several hours of ingestion.