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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 of lactose intolerance include:

  • Nausea
  • Cramps and abdominal pain
  • Painful gas
  • Bloating
  • Diarrhea

Symptoms tend to develop 30 minutes to two hours after drinking milk or eating dairy products. The severity of symptoms varies, depending on the amount of lactose the person ate or drank and the amount the 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 50% of Hispanics; 75% of African Americans, Jews, and Native Americans; and 90% of some Asian populations.

What Causes Lactose Intolerance?

For most people, lactose intolerance develops naturally as they grow older. The small intestine often begins to produce less lactase 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), infections, and injuries to the small intestine can also reduce the amount of lactase available to process lactose properly.

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