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Lactose Intolerance

Who Is Affected By It?

Between 30 and 50 million Americans are lactose intolerant, and certain ethnic and racial populations are more affected than others. Up to 80 percent of African Americans, 80 to 100 percent of American Indians, and 90 to 100 percent of Asian Americans are lactose intolerant. The condition is least common among people of northern European descent.

Causes of Lactose Intolerance

The cause of lactose intolerance is a shortage of the enzyme lactase (lactase deficiency).
Some causes of a lactase deficiency are well known; in other cases, research scientists are not sure why a person develops this deficiency.
There are two general categories of lactase deficiency:
  • Primary lactase deficiency
  • Secondary lactase deficiency.
(Click Cause of Lactose Intolerance for more information on this topic.)


The severity of lactose intolerance symptoms depends on many factors, including the amount of lactose a person can tolerate and a person's age, ethnicity, and digestion rate.
Common symptoms of lactose intolerance, which range from mild to severe, include:
  • Nausea
  • Cramps
  • Abdominal pain
  • Bloating
  • Gas
  • Diarrhea
  • Odd-smelling stool
  • Floating stool.
(Click Lactose Intolerance Symptoms for more information.)
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Lactose Intolerance Information

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