Lactose intolerance overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Mahda Alihashemi M.D. [2] [3]
Overview
Lactose intolerance is the term used to describe a decline in the level of lactase, an enzyme needed for proper metabolization of lactose (a sugar that is a constituent of milk and other dairy products), in human beings.
Historical Perspective
Lactose intolerance first discovered by Hippocrate, ancient Greek physician 2500 years ago. In 1906, Pimmer discovered lactase enzyme in the intestine of infant dogs, pigs, and rats. The association between ethnic and lactose intolerance was discovered in 1966 by Bayless and Rosensweig. In1978, breath hydrogen test was used by Levitt, to diagnose lactose intolerance.
Classification
There is no established system for the classification of lactose intolerance. Lactose intolerance may be classified according to its causes into 2 groups: primary lactose malabsorption and secondary lactose malabsorption. Primary lactose malabsorption may be classified into 3 subtypes: acquired primary lactase deficiency, congenital lactase deficiency and developmental lactase deficiency. Secondary lactose malabsorption occurs as a result of the underlying intestinal diseases such as small intestinal bacterial overgrowth, small intestinal infection such as giardiasis and small intestinalinflammation.
Pathophysiology
It is thought that lactose intolerance is the result of lactose malabsorption that it is caused by low level of small intestinal lactase. Lactose is metabolized by intestinal lactase to galactose and glucose in villous enterocytes. In colon, unabsorbed lactose is converted to hydrogen gas and short chain fatty acids such as acetate, butyrate and propionate by intestinal bacteria and creates symtoms of lactose intolerance. Lactose intolerance is transmitted in an autosomal recessive pattern. Acquired primary lactase deficiency is associated with a CC genotype at -13.9 kb upstream of the lactase gene. On gross and microscopic pathology, there are no characteristic findings of lactose intolerance.
Causes
Some causes of lactose intolerance are well known. Primary lactase deficiency is a condition that develops over time. After about age 2 the body begins to produce less lactase, though most people will not notice symptoms until they are much older. Secondary lactase deficiency occurs when injury to the small intestine or certain digestive diseases reduce the amount of lactase a person produces. These diseases include celiac disease, inflammatory bowel disease, and Crohn’s disease.
Differentiating Lactose Intolerance from other Diseases
The differential diagnosis must distinguish lactose intolerance from milk allergy, which is an abnormal immune response (usually) to milk proteins.
Epidemiology and Demographics
An estimated 70%[1] of adult humans are considered lactose intolerant, it is uncommon in healthy northern westerners and a few others groups. Between 30 and 50 million Americans are lactose intolerant and certain ethnic and racial populations are more affected than others. Up to 80 percent of African Americans, 80 to 100 percent of American Indians, and 90 to 100 percent of Asian Americans are lactose intolerant. The condition is least common among people of northern European descent.
Risk Factors
Babies that are born prematurely are also more likely to be lactose intolerant, because lactase levels do not increase until the third trimester of a woman’s pregnancy.
Natural History, Complications and Prognosis
Lactose intolerance is common, it is not a threat to good health.
Diagnosis
History and Symptoms
Physical Examination
Laboratory Findings
Laboratory tests include hydrogen breath test, stool acidity test, and intestinal biopsy. Since lactose intolerance is the normal state for most adults on a worldwide scale, and not considered a disease condition, diagnosis is not necessarily required.
Electrocardiogram
Chest X Ray
CT
MRI
Echocardiography or Ultrasound
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Lactose intolerance is easy to treat. No treatment can improve the body’s ability to produce lactase, but symptoms can be controlled through diet. The basic principles involved in the management of lactose intolerance include avoiding dietary lactose, substitution of nutrients, using enzyme substitute and regulating calcium intake.
Primary Prevention
Secondary Prevention
Cost-Effectiveness of Thearpy
Future or Investigational Therapies
Case Studies
References
- ↑ Kretchmer N. Lactose and lactase: a historical perspective. Gastroenterology, 1971;61, 805–813