Lactose is a type of sugar found in milk and other dairy products. Lactose intolerance develops when the small intestine does not make enough of an enzyme called lactase. The body needs this enzyme to digest lactose.
Lactase deficiency; Milk intolerance; Disaccharidase deficiency; Dairy product intolerance
Causes, incidence, and risk factors
Babies' bodies make the lactase enzyme so they can digest milk, including breast milk.
Babies born too early (premature) sometimes have lactose intolerance. Children who were born at full term usually do not show signs of the problem until they are at least 3 years old.
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.
- In Caucasians, lactose intolerance often develops in children older than age 5. In African Americans, the problem can occur as early as age 2.
- The condition is normal among adults with Asian, African, or Native American heritage. It is less common in people of northern or western European backgrounds.
Other causes of lactose intolerance include:
- Bowel surgery
- Infections in the small intestine from viruses, bacteria, or parasites (most often seen in children, but can also occur in adults)
- Intestinal diseases such as celiac sprue
Symptoms often occur 30 minutes to 2 hours after having milk products. Large doses of milk products may cause worsesymptoms.
Signs and tests
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 or removing milk products from your diet usually eases symptoms.
Most people with low lactase levels can drink 2 - 4 ounces of milk at one time (up to one-half cup) without having symptoms. Larger (more than 8 oz.) servings may cause problems for people with lactase deficiency.
Milk products may be easier to digest include:
- Buttermilk and cheeses (have less lactose than milk)
- Fermented milk products, such as yogurt
- Goat's milk
- Ice cream, milkshakes, and aged or hard cheeses
- Lactose-free milk and milk products
- Lactase-treated cow's milk for older children and adults
- Soy formulas for infants younger than 2 years
- Soy or rice milk for toddlers
You can add lactase enzymes to regular milk, or take these enzymes in capsule or chewable tablet form.
Not having milk in your diet can lead to a shortage of calcium, vitamin D, riboflavin, and protein. You need1,000 - 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:
- Take calcium supplements
- Eat foods that have more calcium (such as leafy greens, oysters, sardines, canned salmon, shrimp, and broccoli)
- Drink orange juice that contains added calcium
Read food labels. Lactose is also found in some non-milk products -- including some beers.
Symptoms usually go away after removing milk products and other lactose containing products from your diet. Infants or children may have slow growth or weight loss without a change in diet.
Call your health care provider if:
- You have an infant younger than 2 or 3 years old who has symptoms of lactose intolerance.
- Your child is growing slowly or not gaining weight.
- You or your child has symptoms of lactose intolerance and you need information on food substitutes.
- Your symptoms get worse or do not improve with treatment, or you develop new symptoms.
There is no known way to prevent lactose intolerance. You can prevent symptoms by avoiding foods with lactose. Read food labels carefully. Lactose is also found in some non-milk products, including some beers.
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: Saunders Elsevier; 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. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 142.
Review Date: 8/10/2012
Reviewed By: David C. Dugdale, III, MD. Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and George F. Longstreth, MD, Department of Gastroenterology, Kaiser Permanente Medical Care Program, San Diego, California. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.