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Lactose Intolerance

  • Author: Praveen K Roy, MD, AGAF; Chief Editor: Burt Cagir, MD, FACS  more...
 
Updated: Jul 14, 2015
 

Background

Lactose intolerance is a common disorder and is due to the inability to digest lactose into its constituents, glucose and galactose, secondary to low levels of lactase enzyme in the brush border of the duodenum.[1] Lactase deficiency is the most common form of disaccharidase deficiency. Enzyme levels are the highest shortly after birth and decline with aging, despite continued intake of lactose. Within the animal world, nonhuman mammals usually lose the ability to digest lactose as they reach adulthood. Some populations of the human species, including those of Asian, South American, and African descent, have a propensity for developing lactase deficiency. By contrast, races descended from northern Europe or from the northwestern Indian subcontinent are likely to retain the ability to absorb lactose into adulthood.[2]

Symptoms of lactose intolerance include loose stools, abdominal bloating and pain, flatulence, nausea, and borborygmi.[3] A diagnosis or even the suggestion of lactose intolerance leads many people to avoid milk and/or to consume specially prepared food with digestive aids, adding to health care costs.

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Pathophysiology

Lactose, a disaccharide, is present in milk and processed foods. Dietary lactose must be hydrolyzed to a monosaccharide in order to be absorbed by the small intestinal mucosa. A deficiency of intestinal lactase prevents hydrolysis of ingested lactose. The osmotic load of the unabsorbed lactose causes secretion of fluid and electrolytes until osmotic equilibrium is reached. Dilation of the intestine caused by the osmosis induces an acceleration of small intestinal transit, which increases the degree of maldigestion. Within the large intestine, free lactose is fermented by colonic bacteria to yield short-chain fatty acids and hydrogen gas.[4] The combined increase in fecal water, intestinal transit, and generated hydrogen gas accounts for the wide range of gastrointestinal symptoms.

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Etiology

Congenital lactose intolerance is inherited as an autosomal recessive trait and is very rare.[5, 6]

Primary lactose intolerance is due to low levels of lactase, which develop after childhood.

Secondary, or acquired, lactase deficiency may develop in a person with a healthy small intestine during episodes of acute illness. This occurs because of mucosal damage or from medications. Some causes of secondary lactase deficiency are as follows:

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Epidemiology

Frequency

United States statistics

The prevalence of primary lactose intolerance varies according to race. As many as 25% of the white population (prevalence in those from southern European roots) is estimated to have lactose intolerance, while among black, Native American, and Asian American populations, the prevalence of lactose intolerance is estimated at 75-90%.[2]

International statistics

Of the world's population, 75% is estimated to be lactose-deficient. Lactose intolerance is very common among Asian, South American, and African persons.

Race-, sex-, and age-related demographics

Persons of all races are affected by lactose intolerance, with a higher prevalence among Asian, African, and South American persons.

Males and females are equally affected by lactose intolerance. However, of those women who are lactose intolerant, 44% regain the ability to digest lactose during pregnancy. This is probably due to slow intestinal transit and bacterial adaptation during pregnancy.

Among adults, the age of presentation of lactose intolerance is 20-40 years.[5, 7]

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Prognosis

The prognosis of patients with lactose intolerance is excellent with dietary restrictions. Morbidity/mortality include the following:

  • Lactose intolerance is not lethal.
  • Morbidity is low from lactose intolerance.
  • Osteopenia can be a complication of lactose intolerance.

Complications of lactose intolerance may include osteopenia.[8, 9]

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Contributor Information and Disclosures
Author

Praveen K Roy, MD, AGAF Chief of Gastroenterology, Presbyterian Hospital; Medical Director of Endoscopy, Presbyterian Medical Group; Adjunct Associate Research Scientist, Lovelace Respiratory Research Institute

Praveen K Roy, MD, AGAF is a member of the following medical societies: American Gastroenterological Association, American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Coauthor(s)

Homayoun Shojamanesh, MD Former Fellow, Digestive Diseases Branch, National Institutes of Health

Homayoun Shojamanesh, MD is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Showkat Bashir, MD Assistant Professor, Department of Medicine, Division of Gastroenterology, George Washington University, Washington, DC

Showkat Bashir, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Medical Association

Disclosure: Nothing to disclose.

Sarah D Komanapalli, MBBS Resident Physician in Internal Medicine, Marshfield Clinic

Sarah D Komanapalli, MBBS is a member of the following medical societies: American College of Physicians

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

BS Anand, MD Professor, Department of Internal Medicine, Division of Gastroenterology, Baylor College of Medicine

BS Anand, MD is a member of the following medical societies: American Association for the Study of Liver Diseases, American College of Gastroenterology, American Gastroenterological Association, American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Chief Editor

Burt Cagir, MD, FACS Clinical Professor of Surgery, The Commonwealth Medical College; Attending Surgeon, Assistant Program Director, Robert Packer Hospital; Attending Surgeon, Corning Hospital

Burt Cagir, MD, FACS is a member of the following medical societies: American College of Surgeons, American Medical Association, Society for Surgery of the Alimentary Tract

Disclosure: Nothing to disclose.

Additional Contributors

Ronnie Fass, MD, FACP, FACG Chief of Gastroenterology, Head of Neuroenteric Clinical Research Group, Southern Arizona Veterans Affairs Health Care System; Professor of Medicine, Division of Gastroenterology, University of Arizona School of Medicine

Ronnie Fass, MD, FACP, FACG is a member of the following medical societies: American College of Gastroenterology, American College of Physicians-American Society of Internal Medicine, American Gastroenterological Association, American Neurogastroenterology and Motility Society, American Society for Gastrointestinal Endoscopy, Israeli Medical Association

Disclosure: Received grant/research funds from Takeda Pharmaceuticals for conducting research; Received consulting fee from Takeda Pharmaceuticals for consulting; Received honoraria from Takeda Pharmaceuticals for speaking and teaching; Received consulting fee from Vecta for consulting; Received consulting fee from XenoPort for consulting; Received honoraria from Eisai for speaking and teaching; Received grant/research funds from Wyeth Pharmaceuticals for conducting research; Received grant/research funds f.

Douglas M Heuman, MD, FACP, FACG, AGAF Chief of Hepatology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center; Professor, Department of Internal Medicine, Division of Gastroenterology, Virginia Commonwealth University School of Medicine

Douglas M Heuman, MD, FACP, FACG, AGAF is a member of the following medical societies: American Association for the Study of Liver Diseases, American College of Physicians, American Gastroenterological Association

Disclosure: Received grant/research funds from Novartis for other; Received grant/research funds from Bayer for other; Received grant/research funds from Otsuka for none; Received grant/research funds from Bristol Myers Squibb for other; Received none from Scynexis for none; Received grant/research funds from Salix for other; Received grant/research funds from MannKind for other.

Abhishek Choudhary, MD Resident Physician, Department of Internal Medicine, University Hospital of Missouri-Columbia

Abhishek Choudhary, MD is a member of the following medical societies: American College of Physicians

Disclosure: Nothing to disclose.

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