Lactose Intolerance

Author: Praveen K Roy, MD, AGAF; Chief Editor: Julian Katz, MD more...

Updated: Jun 16, 2011

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Background
Pathophysiology
Epidemiology
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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 highest shortly after birth and decline with aging, despite a 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.

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.

Frequency

United States

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

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

Mortality/Morbidity

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

Race

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

Sex

Males and females are equally affected by lactose intolerance.
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.

Age

Among adults, the age of presentation of lactose intolerance is 20-40 years.^{[5, 6]}

Proceed to Clinical Presentation

Contributor Information and Disclosures

Author

Praveen K Roy, MD, AGAF Gastroenterologist, Oschner Clinic Foundation; Clinical Assistant Professor of Medicine, University of New Mexico School of Medicine; Comments and Criticisms Editor, Cochrane Colorectal Cancer Group; Adjunct Associate Research Scientist, Lovelace Respiratory Research Institute; Editor-in-Chief, The Internet Journal of Gasteroenterology; Editorial Board, Signal Transduction Insights; Editorial Board, The Internet Journal of Epidemiology; Editorial Board, Gastrointestinal Endoscopy Review Letter

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

Disclosure: Nothing to disclose.

Coauthor(s)

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.

Mohamed Othman, MD Resident Physician, Department of Internal Medicine, University of New Mexico School of Medicine

Disclosure: Nothing to disclose.

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, and American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Jack Bragg, DO Associate Professor, Department of Clinical Medicine, University of Missouri School of Medicine

Jack Bragg, DO is a member of the following medical societies: American College of Osteopathic Internists and American Osteopathic Association

Disclosure: Nothing to disclose.

Gautam Dehadrai, MD Department Chair, Section Chief, Department of Interventional Radiology, Norman Regional Hospital

Gautam Dehadrai, MD is a member of the following medical societies: American College of Radiology, Medical Council of India, and Radiological Society of North America

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, and American Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Ronnie Fass, MD Chief of Gastroenterology, Southern Arizona VA Health Care System; Professor of Medicine, Division of Gastroenterology, University of Arizona School of Medicine

Ronnie Fass, MD 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 Motility Society, American Society for Gastrointestinal Endoscopy, and Israel Medical Association

Disclosure: Takeda Pharmaceuticals Grant/research funds Conducting research; Takeda Pharmaceuticals Consulting fee Consulting; Takeda Pharmaceuticals Honoraria Speaking and teaching; Vecta Consulting fee Consulting; XenoPort Consulting fee Consulting; Eisai Honoraria Speaking and teaching; Wyeth Pharmaceuticals Conducting research; AstraZeneca Grant/research funds Conducting research; Eisai Consulting fee Consulting

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

Disclosure: Medscape Salary Employment

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, and American Gastroenterological Association

Disclosure: Novartis Grant/research funds Other; Bayer Grant/research funds Other; Otsuka Grant/research funds None; Bristol Myers Squibb Grant/research funds Other; Scynexis None None; Salix Grant/research funds Other; MannKind Other

Alex J Mechaber, MD, FACP Senior Associate Dean for Undergraduate Medical Education, Associate Professor of Medicine, University of Miami Miller School of Medicine

Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine

Disclosure: Nothing to disclose.

Chief Editor

Julian Katz, MD Clinical Professor of Medicine, Drexel University College of Medicine

Julian Katz, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Geriatrics Society, American Medical Association, American Society for Gastrointestinal Endoscopy, American Society of Law, Medicine & Ethics, American Trauma Society, Association of American Medical Colleges, and Physicians for Social Responsibility

Disclosure: Nothing to disclose.

References

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