KidsMD Health Topics

Lactose Intolerance

  • Lactose is a sugar found in milk products; lactose intolerance occurs when the body is unable to digest milk products due to the lack of a digestive enzyme called lactase.

    Boston Children's Hospital
    300 Longwood Avenue
    Boston MA 02115


  • What is lactase?

    Lactase is an enzyme that is normally produced in the small intestine, where it breaks down lactose into a form that can be absorbed by the blood. A lack of lactase can cause uncomfortable symptoms for some people; those who exhibit symptoms are said to be "lactose intolerant."

    How common is lactose intolerance?

    30 to 50 million Americans are lactose intolerant.

    Is this disorder more common among certain ethnic groups?

    • 80 percent of all African-Americans and Native Americans are lactose intolerant.
    • Over 90 percent of Asian-Americans are lactose intolerant.
    • Lactose intolerance is least common among Americans with a Northern European heritage.

    What causes lactose intolerance?

    In young children, lactose intolerance is usually caused by digestive diseases or injuries to the small intestine. But most cases of lactose intolerance develop over a period of many years in adolescents and adults.

    What are the symptoms of lactose intolerance?

    Each individual may experience symptoms differently, but common symptoms—which typically begin about 30 minutes to two hours after consuming food or beverages containing lactose—include:

    Severity varies depending on the amount of lactose consumed and the amount your child can tolerate.

  • The most common diagnostic tests (performed on an outpatient basis at the hospital) measure the absorption of lactose in your child's digestive system include the following:

    • Lactose tolerance test - This test measures the absorption of lactose in the digestive system. After fasting, your child drinks a liquid that contains lactose. The diarrheal stools are then tested for lactose for the next 24 hours. Undigested lactose fermented by bacteria in the colon creates lactic acid and other fatty acids, which can be detected in a stool sample, along with glucose as a result of unabsorbed lactose.

    • Hydrogen breath test - Your child drinks a lactose-heavy beverage. Her breath is then analyzed at regular intervals to measure the amount of hydrogen. Undigested lactose in the colon is fermented by bacteria, resulting in the production of various gases, including hydrogen. When high levels of hydrogen are present in the breath, improper digestion of lactose is diagnosed.

    • Your child's physician may recommend taking lactase enzymes.

    • Symptoms are often best controlled with a proper diet.

    • Because milk and other dairy products are often a child's major source of calcium, and because calcium is essential for healthy bones and growth, you must ensure that your lactose-intolerant child gets enough calcium from other sources. Nondairy foods that are high in calcium include:

    • green vegetables, such as broccoli and kale

    • fish, such as salmon and sardines

    • yogurt with active cultures may be a good source of calcium for many people with lactose intolerance - evidence shows that the bacterial cultures used in making yogurt produce some of the lactase enzyme required for proper digestion

    Your child's physician may prescribe a calcium supplement if your child is unable to get enough calcium from food.

    Vitamin D is necessary for the body to absorb calcium; therefore, you child's diet should provide an adequate supply of vitamin D. Sources of vitamin D include eggs and liver. Sunlight can also provide vitamin D.

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