eMedicine Specialties > Gastroenterology > Intestine

Lactose Intolerance

Author: Praveen K Roy, MD, Comments and Criticisms Editor, Cochrane Colorectal Cancer Group
Coauthor(s): Abhishek Choudhary, MD, Resident, Department of Internal Medicine, University Hospital of Missouri; Mohamed Othman, MD, Staff Physician, Department of Internal Medicine, University of New Mexico School of Medicine; Homayoun Shojamanesh, MD, Former Fellow, Digestive Diseases Branch, National Institutes of Health; Jack Bragg, DO, FACOI, Assistant Professor, Department of Clinical Medicine, University of Missouri School of Medicine; Gautam Dehadrai, MD, Department Chair, Section Chief, Department of Interventional Radiology, Norman Regional Hospital
Contributor Information and Disclosures

Updated: Aug 12, 2008

Introduction

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. 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.

Symptoms of lactose intolerance include loose stools, abdominal bloating and pain, flatulence, nausea, and borborygmi. 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. 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%.

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.

Clinical

History

  • History in patients with lactose intolerance may include abdominal fullness/bloating, nausea, abdominal pain, diarrhea, and flatulence.
  • The symptoms of irritable bowel syndrome (IBS) resemble those of lactose intolerance and can easily be confused. Some patients with IBS can also have lactose intolerance. Restriction of milk products in these patients may relieve the symptoms of IBS.

Physical

  • Physical examination findings very often are normal.
  • Borborygmi may be present.

Causes

  • Congenital lactose intolerance is inherited as an autosomal recessive trait and is very rare.
  • 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:

More on Lactose Intolerance

Overview: Lactose Intolerance
Differential Diagnoses & Workup: Lactose Intolerance
Treatment & Medication: Lactose Intolerance
Follow-up: Lactose Intolerance
References
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References

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Further Reading

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Keywords

lactose intolerance, lactose intolerant, milk, milk allergy, lactase, lactose allergy, lactase deficiency, milk products, dairy allergy, dairy allergies, dairy products, food allergy, food allergies, lactose malabsorption, lactose maldigestion, lactose deficient, lactose tolerance test, milk tolerance test, glucose, galactose, hypolactasia, osteopenia, osteoporosis, disaccharidase deficiency

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Contributor Information and Disclosures

Author

Praveen K Roy, MD, Comments and Criticisms Editor, Cochrane Colorectal Cancer Group
Praveen K Roy, MD is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, and Canadian Association of Gastroenterology
Disclosure: Nothing to disclose.

Coauthor(s)

Abhishek Choudhary, MD, Resident, Department of Internal Medicine, University Hospital of Missouri
Abhishek Choudhary, MD is a member of the following medical societies: American College of Physicians
Disclosure: Nothing to disclose.

Mohamed Othman, MD, Staff 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 Gastroenterological Association, American Medical Association, and American Society for Gastrointestinal Endoscopy
Disclosure: Nothing to disclose.

Jack Bragg, DO, FACOI, Assistant Professor, Department of Clinical Medicine, University of Missouri School of Medicine
Jack Bragg, DO, FACOI 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.

Medical Editor

Ronnie Fass, MD, Director of GI Motility Laboratory, Tucson VA Medical Center, Associate Professor, Department of Internal 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: Nothing to disclose.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

Douglas M Heuman, MD, FACP, Director of Hepatology, McGuire Veterans Affairs Medical Center, Professor, Department of Internal Medicine, Division of Gastroenterology, Virginia Commonwealth University School of Medicine
Douglas M Heuman, MD, FACP 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: Nothing to disclose.

CME Editor

Alex J Mechaber, MD, FACP, Assistant Dean for Medical Curriculum, Associate Professor of Medicine, Division of General Internal 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; Consulting Staff, Department of Medicine, Section of Gastroenterology and Hepatology, Hospital of the Medical College of Pennsylvania
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 and Ethics, American Trauma Society, Association of American Medical Colleges, and Physicians for Social Responsibility
Disclosure: Nothing to disclose.

 
 
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