- Author: Praveen K Roy, MD, AGAF; Chief Editor: Burt Cagir, MD, FACS more...
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 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.
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.
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.
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:
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%.
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]
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]
Vesa TH, Marteau P, Korpela R. Lactose intolerance. J Am Coll Nutr. 2000 Apr. 19(2 Suppl):165S-175S. [Medline].
Newcomer AD, McGill DB, Thomas PJ, et al. Tolerance to lactose among lactase-deficient American Indians. Gastroenterology. 1978 Jan. 74(1):44-6. [Medline].
Di Stefano M, Miceli E, Mazzocchi S, et al. Visceral hypersensitivity and intolerance symptoms in lactose malabsorption. Neurogastroenterol Motil. 2007 Nov. 19(11):887-95. [Medline].
Zhong Y, Priebe MG, Vonk RJ, et al. The role of colonic microbiota in lactose intolerance. Dig Dis Sci. 2004 Jan. 49(1):78-83. [Medline].
Auricchio S, Rubino A, Landolt M, Semenza G, Prader A. Isolated intestinal lactase deficiency in the adult. Lancet. 1963 Aug 17. 2(7303):324-6. [Medline].
Upton J, Mackay R, George P. A simple gene test for lactose intolerance/adult hypolactasia. N Z Med J. 2007 Nov 9. 120(1265):U2817. [Medline].
Kern F Jr, Struthers JE Jr. Intestinal lactase deficiency and lactose intolerance in adults. JAMA. 1966 Mar 14. 195(11):927-30. [Medline].
Kudlacek S, Freudenthaler O, Weissboeck H, et al. Lactose intolerance: a risk factor for reduced bone mineral density and vertebral fractures?. J Gastroenterol. 2002. 37(12):1014-9. [Medline].
Di Stefano M, Veneto G, Malservisi S, et al. Lactose malabsorption and intolerance and peak bone mass. Gastroenterology. 2002 Jun. 122(7):1793-9. [Medline].
Bayless TM, Rothfeld B, Massa C, et al. Lactose and milk intolerance: clinical implications. N Engl J Med. 1975 May 29. 292(22):1156-9. [Medline].
Mishkin S. Dairy sensitivity, lactose malabsorption, and elimination diets in inflammatory bowel disease. Am J Clin Nutr. 1997 Feb. 65(2):564-7. [Medline].
Beyerlein L, Pohl D, Delco F, et al. Correlation between symptoms developed after the oral ingestion of 50 g lactose and results of hydrogen breath testing for lactose intolerance. Aliment Pharmacol Ther. 2008 Apr. 27(8):659-65. [Medline].
Hermans MM, Brummer RJ, Ruijgers AM, et al. The relationship between lactose tolerance test results and symptoms of lactose intolerance. Am J Gastroenterol. 1997 Jun. 92(6):981-4. [Medline].
Arola H. Diagnosis of hypolactasia and lactose malabsorption. Scand J Gastroenterol Suppl. 1994. 202:26-35. [Medline].
Carroccio A, Montalto G, Cavera G, et al. Lactose intolerance and self-reported milk intolerance: relationship with lactose maldigestion and nutrient intake. Lactase Deficiency Study Group. J Am Coll Nutr. 1998 Dec. 17(6):631-6. [Medline].
Suarez FL, Savaiano DA, Levitt MD. A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance. N Engl J Med. 1995 Jul 6. 333(1):1-4. [Medline].
Patel YT, Minocha A. Lactose intolerance: diagnosis and management. Compr Ther. 2000 Winter. 26(4):246-50. [Medline].
Suarez FL, Savaiano DA, Levitt MD. Review article: the treatment of lactose intolerance. Aliment Pharmacol Ther. 1995 Dec. 9(6):589-97. [Medline].
Vonk RJ, Priebe MG, Koetse HA, et al. Lactose intolerance: analysis of underlying factors. Eur J Clin Invest. 2003 Jan. 33(1):70-5. [Medline].
Suarez FL, Savaiano D, Arbisi P, et al. Tolerance to the daily ingestion of two cups of milk by individuals claiming lactose intolerance. Am J Clin Nutr. 1997 May. 65(5):1502-6. [Medline].
Jarvinen RM, Loukaskorpi M, Uusitupa MI. Tolerance of symptomatic lactose malabsorbers to lactose in milk chocolate. Eur J Clin Nutr. 2003 May. 57(5):701-5. [Medline].
Beja-Pereira A, Luikart G, England PR, et al. Gene-culture coevolution between cattle milk protein genes and human lactase genes. Nat Genet. 2003 Dec. 35(4):311-3. [Medline].
Born P, Sekatcheva M, Rosch T, et al. Carbohydrate malabsorption in clinical routine: a prospective observational study. Hepatogastroenterology. 2006 Sep-Oct. 53(71):673-7. [Medline].
Hammer HF, Hammer J. Diarrhea caused by carbohydrate malabsorption. Gastroenterol Clin North Am. 2012 Sep. 41(3):611-27. [Medline].
Lomer MC, Parkes GC, Sanderson JD. Review article: lactose intolerance in clinical practice--myths and realities. Aliment Pharmacol Ther. 2008 Jan 15. 27(2):93-103. [Medline].