Lactose is a type of sugar found in milk and other dairy products. An enzyme called lactase is needed by the body to digest lactose.
Lactose intolerance develops when the small intestine does not make enough of this enzyme.
Babies' bodies make the lactase enzyme so they can digest milk, including breast milk.
Lactose intolerance is very common in adults. It is rarely dangerous. Around 30 million American adults have some degree of lactose intolerance by age 20.
An illness that involves or injury your small intestine may cause less of the lactase enzyme to be made. Treatment of these illnesses may improve the symptoms of lactose intolerance. These may include:
Babies may be born with a genetic defect and are not able to make any of the lactase enzyme.
Symptoms often occur 30 minutes to 2 hours after having milk products. Symptoms may be worse when you consume large amounts.
Other intestinal problems, such as irritable bowel syndrome, may cause the same symptoms as lactose intolerance.
Tests to help diagnose lactose intolerance include:
Cutting down your intake of milk products that contain lactose from your diet most often eases symptoms. Also look at food labels for hidden sources of lactose in non-milk products (even some beers) and avoid these.
Most people with low lactase levels can drink up to one-half cup of milk at one time (2 to 4 ounces) without having symptoms. Larger servings (more than 8 oz.) may cause problems for people with the deficiency.
Milk products that may be easier to digest include:
You can add lactase enzymes to regular milk. You can also take these enzymes as capsules or chewable tablets. There are also many lactose-free dairy products available.
Not having milk in your diet can lead to a shortage of calcium, vitamin D, riboflavin, and protein. You need 1,000 to 1,500 mg of calcium each day depending on your age and gender. Some things you can do to get more calcium in your diet are:
Symptoms most often go away when you remove milk and other sources of lactose from your diet. Without dietary changes, infants or children may have growth problems.
Call your health care provider if:
There is no known way to prevent lactose intolerance. You can prevent symptoms by avoiding foods with lactose.
Lactase deficiency; Milk intolerance; Disaccharidase deficiency; Dairy product intolerance
Hogenauer C, Hammer HF. Maldigestion and malabsorption. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 9th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 101.
Lactose intolerance. The National Digestive Diseases Information Clearinghouse (NDDIC). NIH Publication No. 09-2751. June 2009, updated April 12, 2012.
Semrad CE. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 142.
Updated by: Jenifer K. Lehrer, MD, Department of Gastroenterology, Frankford-Torresdale Hospital, Aria Health System, Philadelphia, PA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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