Lactose Intolerance
The digestive tract
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?
Lactose intolerance is a condition in which people have digestive symptoms—such as bloating, diarrhea, and gas—after eating or drinking milk or milk products.
Lactase deficiency and lactose malabsorption may lead to lactose intolerance:
- Lactase deficiency. In people who have a lactase deficiency, the small intestine produces low levels of lactase and cannot digest much lactose.
- Lactose malabsorption. Lactase deficiency may cause lactose malabsorption. In lactose malabsorption, undigested lactose passes to the colon. The colon, part of the large intestine, absorbs water from stool and changes it from a liquid to a solid form. In the colon, bacteria break down undigested lactose and create fluid and gas. Not all people with lactase deficiency and lactose malabsorption have digestive symptoms.
People have lactose intolerance when lactase deficiency and lactose malabsorption cause digestive symptoms. Most people with lactose intolerance can eat or drink some amount of lactose without having digestive symptoms. Individuals vary in the amount of lactose they can tolerate.
People sometimes confuse lactose intolerance with a milk allergy. While lactose intolerance is a digestive system disorder, a milk allergy is a reaction by the body’s immune system to one or more milk proteins. An allergic reaction to milk can be life threatening even if the person eats or drinks only a small amount of milk or milk product. A milk allergy most commonly occurs in the first year of life, while lactose intolerance occurs more often during adolescence or adulthood.- 1,2
1- Boyce 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.
2- Suchy 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.
What are the symptoms of lactose intolerance?
Common symptoms of lactose intolerance include
- abdominal bloating, a feeling of fullness or swelling in the abdomen
- abdominal pain
- diarrhea
- gas
- nausea
Symptoms occur 30 minutes to 2 hours after consuming milk or milk products. Symptoms range from mild to severe based on the amount of lactose the person ate or drank and the amount a person can tolerate.
How does lactose intolerance affect health?
In addition to causing unpleasant symptoms, lactose intolerance may affect people’s health if it keeps them from consuming enough essential nutrients, such as calcium and vitamin D. People with lactose intolerance may not get enough calcium if they do not eat calcium-rich foods or do not take a dietary supplement that contains calcium. Milk and milk products are major sources of calcium and other nutrients in the diet. Calcium is essential at all ages for the growth and maintenance of bones. A shortage of calcium intake in children and adults may lead to bones that are less dense and can easily fracture later in life, a condition called osteoporosis.
How is lactose intolerance managed?
Many people can manage the symptoms of lactose intolerance by changing their diet. Some people may only need to limit the amount of lactose they eat or drink. Others may need to avoid lactose altogether. Using lactase products can help some people manage their symptoms.
For people with secondary lactase deficiency, treating the underlying cause improves lactose tolerance. In infants with developmental lactase deficiency, the ability to digest lactose improves as the infants mature. People with primary and congenital lactase deficiency cannot change their body’s ability to produce lactase.
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