Lactose Intolerance National Digestive Diseases Information Clearinghouse What is lactose? Lactose is a sugar found in milk and milk products. The small intestine—the organ where most food digestion and nutrient absorption take place—produces an enzyme called lactase. Lactase breaks down lactose into two simpler forms of sugar: glucose and galactose. The body then absorbs these simpler sugars into the bloodstream. What is lactose intolerance? Large Lactose intolerance is a condition in which intestine people have digestive symptoms—such as bloating, diarrhea, and gas—after eating or Colon drinking milk or milk products. (shaded) Small Lactase deficiency and lactose malabsorption intestine may lead to lactose intolerance: • Lactase deficiency. In people who have The digestive tract a lactase deficiency, the small intestine produces low levels of lactase and cannot digest much lactose. from stool and changes it from a liquid to a solid form. In the colon, bacteria • Lactose malabsorption. Lactase break down undigested lactose and deficiency may cause lactose create fluid and gas. Not all people malabsorption. In lactose with lactase deficiency and lactose malabsorption, undigested lactose malabsorption have digestive symptoms. passes to the colon. The colon, part of the large intestine, absorbs water People have lactose intolerance when lactase disorder, a milk allergy is a reaction by the deficiency and lactose malabsorption cause body’s immune system to one or more milk digestive symptoms. Most people with proteins. An allergic reaction to milk can lactose intolerance can eat or drink some be life threatening even if the person eats or amount of lactose without having digestive drinks only a small amount of milk or milk symptoms. Individuals vary in the amount of product. A milk allergy most commonly lactose they can tolerate. occurs in the first year of life, while lactose intolerance occurs more often during People sometimes confuse lactose adolescence or adulthood.1,2 intolerance with a milk allergy. While lactose intolerance is a digestive system Four Types of Lactase • Secondary lactase deficiency results from injury to the small Deficiency intestine. Infection, diseases, or Four types of lactase deficiency may lead other problems may injure the small to lactose intolerance: intestine. Treating the underlying • Primary lactase deficiency, also cause usually improves the lactose called lactase nonpersistence, is tolerance. the most common type of lactase • Developmental lactase deficiency deficiency. In people with this may occur in infants born condition, lactase production prematurely. This condition usually declines over time. This decline lasts for only a short time after they often begins at about age 2; are born. however, the decline may begin • Congenital lactase deficiency is an later. Children who have lactase extremely rare disorder in which the deficiency may not experience small intestine produces little or no symptoms of lactose intolerance lactase enzyme from birth. Genes until late adolescence or adulthood. inherited from parents cause this Researchers have discovered that disorder. some people inherit genes from their parents that may cause a primary lactase deficiency. 1Boyce JA, Assa’ad A, Burks AW, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. Journal of Allergy and Clinical Immunology. 2010;126(6 suppl.):S1–S58. 2Suchy FJ, Brannon PM, Carpenter TO, et al. National Institutes of Health Consensus Development Conference: lactose intolerance and health. Annals of Internal Medicine. 2010;152(12):792–796. 2 Lactose Intolerance Who is more likely to have for the growth and maintenance of bones. A shortage of calcium intake in children lactose intolerance? and adults may lead to bones that are less In the United States, some ethnic and racial dense and can easily fracture later in life, a populations are more likely to have lactose condition called osteoporosis. intolerance than others, including African Americans, Hispanics/Latinos, American Indians, and Asian Americans. The How is lactose intolerance condition is least common among Americans diagnosed? of European descent.2 A health care provider makes a diagnosis of lactose intolerance based on What are the symptoms • medical, family, and diet history, of lactose intolerance? including a review of symptoms Common symptoms of lactose intolerance • a physical exam include • medical tests • abdominal bloating, a feeling of fullness Medical, family, and diet history. A health or swelling in the abdomen care provider will take a medical, family, • abdominal pain and diet history to help diagnose lactose • diarrhea intolerance. During this discussion, the health care provider will review a patient’s • gas symptoms. However, basing a diagnosis on • nausea symptoms alone may be misleading because digestive symptoms can occur for many Symptoms occur 30 minutes to 2 hours after reasons other than lactose intolerance. consuming milk or milk products. Symptoms For example, other conditions such as range from mild to severe based on the irritable bowel syndrome, celiac disease, amount of lactose the person ate or drank inflammatory bowel disease, or small bowel and the amount a person can tolerate. bacterial overgrowth can cause digestive symptoms. How does lactose Physical exam. A physical exam may intolerance affect health? help diagnose lactose intolerance or rule In addition to causing unpleasant symptoms, out other conditions that cause digestive lactose intolerance may affect people’s symptoms. During a physical exam, a health health if it keeps them from consuming care provider usually enough essential nutrients, such as calcium • checks for abdominal bloating and vitamin D. People with lactose intolerance may not get enough calcium if • uses a stethoscope to listen to sounds they do not eat calcium-rich foods or do within the abdomen not take a dietary supplement that contains • taps on the abdomen to check for calcium. Milk and milk products are major tenderness or pain sources of calcium and other nutrients in the diet. Calcium is essential at all ages 3 Lactose Intolerance A health care provider may recommend provider will give the child’s parent eliminating all milk and milk products from or caretaker a container for collecting a person’s diet for a short time to see if the the stool specimen. The parent or symptoms resolve. Symptoms that go away caretaker returns the sample to the when a person eliminates lactose from his or health care provider, who sends it to a her diet may confirm the diagnosis of lactose lab for analysis. intolerance. Medical tests. A health care provider How much lactose can may order special tests to provide more a person with lactose information. Health care providers intolerance have? commonly use two tests to measure how well a person digests lactose: Most people with lactose intolerance can tolerate some amount of lactose in their • Hydrogen breath test. This test diet and do not need to avoid milk or milk measures the amount of hydrogen in products completely. Avoiding milk and milk a person’s breath. Normally, only a products altogether may cause people to take small amount of hydrogen is detectable in less calcium and vitamin D than they need. in the breath when a person eats or See the “Calcium and Vitamin D” section. drinks and digests lactose. However, undigested lactose produces high levels Individuals vary in the amount of lactose they of hydrogen. For this test, the patient can tolerate. A variety of factors—including drinks a beverage that contains a known how much lactase the small intestine amount of lactose. A health care produces—can affect how much lactose an provider asks the patient to breathe into individual can tolerate. For example, one a balloon-type container that measures person may have severe symptoms after breath hydrogen level. In most cases, drinking a small amount of milk, while a health care provider performs this another person can drink a large amount test at a hospital, on an outpatient without having symptoms. Other people can basis. Smoking and some foods and easily eat yogurt and hard cheeses such as medications may affect the accuracy cheddar and Swiss, while they are not able of the results. A health care provider to eat or drink other milk products without will tell the patient what foods or having digestive symptoms. medications to avoid before the test. Research suggests that adults and • Stool acidity test. Undigested lactose adolescents with lactose malabsorption could creates lactic acid and other fatty acids eat or drink at least 12 grams of lactose in that a stool acidity test can detect in a one sitting without symptoms or with only stool sample. Health care providers minor symptoms. This amount is the amount sometimes use this test to check of lactose in 1 cup of milk. People with acidity in the stools of infants and lactose malabsorption may be able to eat or young children. A child may also have drink more lactose if they eat it or drink it glucose in his or her stool as a result with meals or in small amounts throughout 2 of undigested lactose. The health care the day. 4 Lactose Intolerance How is lactose intolerance People with lactose intolerance are generally more likely to tolerate hard cheeses, such managed? as cheddar or Swiss, than a glass of milk. A Many people can manage the symptoms of 1.5-ounce serving of low-fat hard cheese has lactose intolerance by changing their diet. less than 1 gram of lactose, while a 1-cup Some people may only need to limit the serving of low-fat milk has about 11 to amount of lactose they eat or drink. Others 13 grams of lactose.2 may need to avoid lactose altogether. Using lactase products can help some people However, people with lactose intolerance are manage their symptoms. also more likely to tolerate yogurt than milk, even though yogurt and milk have similar For people with secondary lactase amounts of lactose.2 deficiency, treating the underlying cause improves lactose tolerance.