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Lactose intolerance: Clinical manifestations, diagnosis, and management

Robert K Montgomery, PhD
Richard J Grand, MD
Hans A Büller, MD
Section Editor
Lawrence S Friedman, MD
Deputy Editor
Shilpa Grover, MD, MPH


Intolerance to lactose-containing foods is common [1]. Clinical symptoms of lactose intolerance include diarrhea, abdominal pain, and flatulence after ingestion of milk or milk-containing products. These symptoms have been attributed to low levels of small intestinal lactase, which may be due to mucosal injury or, much more commonly, reduced genetic expression of the enzyme lactase-phlorizin hydrolase. This topic will review the clinical manifestations, diagnosis, and management of lactose intolerance. Other causes of malabsorption are discussed in detail, separately. (See "Mechanisms of nutrient absorption and malabsorption" and "Clinical features and diagnosis of malabsorption" and "Overview of the treatment of malabsorption".)


Lactase deficiency – Lactase deficiency is characterized by an intestinal brush border lactase enzyme activity that is lower than that of normal infants.

Lactose malabsorption – Lactose malabsorption is characterized by a failure of the small bowel to absorb a sizable fraction of ingested lactose.

Lactose intolerance – Lactose intolerance is a clinical syndrome in which lactose ingestion causes symptoms (eg, abdominal pain, bloating, flatulence, diarrhea) due to lactose malabsorption.


The true prevalence of lactose intolerance is unclear due to methodological limitations of existing studies that have used varying definitions of lactose intolerance. Evaluation of epidemiological trends suggests that the prevalence of lactose intolerance varies across racial and ethnic groups, with the lowest prevalence in European Americans and higher prevalence in African Americans, Hispanic Americans, Asian Americans, and Native Americans. The prevalence of lactose malabsorption is low in children younger than six years and increases with age [2,3].


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Literature review current through: Sep 2016. | This topic last updated: Jun 29, 2015.
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