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| ==Epidemiology and Demographics== | | ==Epidemiology and Demographics== |
| An estimated 70%<ref name="Kretchmer1"> Kretchmer N. ''Lactose and lactase: a historical perspective''. Gastroenterology, 1971;61, 805–813</ref> of adult humans are considered lactose intolerant, it is uncommon in healthy northern westerners and a few others groups. | | An estimated 70%<ref name="Kretchmer1"> Kretchmer N. ''Lactose and lactase: a historical perspective''. Gastroenterology, 1971;61, 805–813</ref> of adult humans are considered lactose intolerant, it is uncommon in healthy northern westerners and a few others groups. |
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| ==Classification==
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| There are three major types of lactose intolerance:<ref name="Melvin"> [http://aappolicy.aappublications.org/cgi/content/full/pediatrics;118/3/1279|Melvin B. Heyman. ''Lactose Intolerance in Infants, Children, and Adolescents''. PEDIATRICS Vol. 118 No. 3 September 2006, pp. 1279-1286 (doi:10.1542/peds.2006-1721)]</ref>
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| #Primary lactose intolerance. Environmentally induced by weaning in non dairy consuming societies. In most Asian and African cultures, mother's milk is the only commonly available milk and so milk consumption beyond infancy is not commonplace, therefore children become weaned, which is the same weaning process for all mammals (domesticated and wild). However societies such as the japanese where milk consumption has been on the increase, demonstrate that notwithstanding the genetic predisposition to lactose intolerance, they now present lower prevalence of lactose intolerance.<ref name="Yoshida">[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1234085&dopt=Abstract ''Studies on the etiology of milk intolerance in Japanese adults'', Yoshida Y, Sasaki G, Goto S, Yanagiya S, Takashina K, Gastroenterol Jpn.;10(1):29–34, 1975]</ref> For any given individual the degree of weaning is probably genetically influenced.
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| #Secondary lactose intolerance. Environmentally induced, resulting from certain [[gastrointestinal diseases]], including exposure to [[intestinal parasites]] such as [[giardia]].<ref> [http://www.tulane.edu/~wiser/protozoology/notes/intes.html "Intestinal Protozoa" Mark Wiser 2000] </ref><ref>[http://www.emedicine.com/emerg/topic215.htm "Giardiasis" Andre Pennardt February 22, 2006] </ref> In such cases the production of lactase may be permanently disrupted.[http://www.aafp.org/afp/20020501/1845.html] + (Wiser 2000, Pennardt 2006).
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| #Congenital lactase deficiency present at birth and diagnosed in early infancy.
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| Without lactase, the [[lactose]] [[disaccharide]] in many dairy products remains uncleaved and can not be absorbed through the intestinal wall into the bloodstream, so remains in the intestines. Enteral [[bacterium|bacteria]] adapt to the relative abundance of this undigested sugar and their [[operon]]s quickly switch over to lactose [[metabolism]], which produces copious amounts of gas by [[fermentation (biochemistry)|fermentation]].
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| This also causes a range of unpleasant abdominal symptoms, including stomach [[cramp]]s, [[bloating]], [[flatulence]] and [[diarrhea]]. As with other unabsorbed sugars ([[mannitol]]), the lactose raises the [[osmotic]] pressure of the [[colon (anatomy)|colon]] contents, preventing the colon from reabsorbing water and hence causing a [[laxative]] effect to add to the excessive gas production.
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| ==References== | | ==References== |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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.
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.
References
- ↑ Kretchmer N. Lactose and lactase: a historical perspective. Gastroenterology, 1971;61, 805–813