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Medical Author:

Jay W. Marks, MD

Jay W. Marks, MD

Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.

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Medical Editor:

Bhupinder Anand, MD

In this Article

• What is lactose intolerance?
• What causes lactose intolerance?
• What are the symptoms of lactose intolerance?
• How are lactase deficiency and lactose intolerance diagnosed?
• Elimination diet
• Milk challenge
• Breath test
• Blood glucose test
• Stool acidity test
• What are the sources of lactose in the diet?
• How is lactose intolerance treated?
• What are the long-term consequences of lactose intolerance?
• What is new in lactose intolerance?
• Lactose Intolerance At A Glance
• Patient Comments: Lactose Intolerance - Causes
• Patient Comments: Lactose Intolerance - Symptoms
• Find a local Gastroenterologist in your town
• Lactose Intolerance Index

The important long-term health consequence of lactose intolerance is calcium deficiency that leads to osteoporosis. Less commonly, vitamin D deficiency may occur and compound the bone disease. Both of these health issues can be prevented easily by calcium and vitamin D supplements. The real problem is that many lactose intolerant people who consciously or unconsciously avoid milk do not realize that they need supplements.

It is now possible to test the DNA of individuals to make a diagnosis of lactase deficiency. This is likely to be an important research tool for studying lactase deficiency. It is still too early to know how helpful this sophisticated test will be in the clinical evaluation and treatment of patients. It is an expensive test. Moreover, the test is not very good at distinguishing between lactase deficiency and lactose intolerance since the symptoms of lactose intolerance vary in severity among individuals. The important question to answer is, does lactose cause symptoms, and not, whether an individual is lactase deficient.

In 1998, scientists were able to make lactose intolerant rats tolerant to lactose by transferring the gene for lactase to their intestinal lining cells. It is unlikely that this type of gene therapy will find much of an application in people. Nevertheless, it is a fascinating example of what science can accomplish.

• Lactose intolerance is an inability to digest lactose, the main sugar in milk, that gives rise to gastrointestinal symptoms.

• Lactose intolerance is caused by a deficiency of the intestinal enzyme lactase that splits lactose into two smaller sugars, glucose and galactose, and allows lactose to be absorbed from the intestine.

• The primary symptoms of lactose intolerance are diarrhea, flatulence (passing gas), and abdominal pain. Abdominal bloating, abdominal distention, and nausea also may occur.

• Lactose intolerance can be diagnosed by eliminating lactose from the diet, milk challenge, breath test, blood glucose test, stool acidity test, and intestinal biopsy.

• Lactose intolerance is treated with dietary changes, supplements of lactase enzyme, and adaptation to increasing amounts of milk.

• Avoidance of milk and milk-containing products can lead to a dietary deficiency of calcium and vitamin D that, in turn, can lead to bone disease (osteoporosis).

REFERENCE: eMedicine.com. Lactose Intolerance.
<http://emedicine.medscape.com/article/187249-overview>

Previous contributing author Dennis Lee, M.D.