Editing Lactose intolerance (section)

{{Short description|Inability to digest lactose}}
{{distinguish|Milk allergy}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{Infobox medical condition (new)
| name            = Lactose intolerance
| synonyms        = Lactase deficiency, hypolactasia, alactasia
| image           = Lactose Haworth.svg
| caption         = Lactose is made up of [[disaccharide|two simple sugars]]
| field           = [[Gastroenterology]]
| symptoms        = Abdominal pain, [[bloating]], [[diarrhea]], [[flatulence]], [[nausea]]<ref name=NIH2014Dig/>
| complications   = Does not cause damage to the GI tract<ref name=Heyman2006/>
| onset           = 30–120 minutes after consuming dairy products<ref name=NIH2014Dig/>
| causes          = Non-increased ability to digest [[lactose]] (genetic, small intestine injury)<ref name=NIH2014Dig/>
| differential    = [[Irritable bowel syndrome]], [[celiac disease]], [[inflammatory bowel disease]], [[milk allergy]]<ref name=NIH2014Dig/>
| treatment       = Decreasing lactose in the diet, [[lactase supplements]], treat the underlying cause<ref name=NIH2014Dig/>
| medication      = Lactase
| frequency       = ~65% of people worldwide (less common in Northern Europeans and East Africans)<ref name=Stat2020/>
}}
<!-- Definition and symptoms -->

'''Lactose intolerance''' is caused by a lessened ability or a complete inability to digest [[lactose]], a sugar found in [[dairy product]]s.<ref name=NIH2014Dig/> Humans vary in the amount of lactose they can tolerate before symptoms develop.<ref name=NIH2014Dig/> Symptoms may include [[abdominal pain]], [[bloating]], [[diarrhea]], [[flatulence]], and [[nausea]].<ref name=NIH2014Dig/> These symptoms typically start thirty minutes to two hours after eating or drinking something containing lactose,<ref name=NIH2014Dig/> with the severity typically depending on the amount consumed.<ref name=NIH2014Dig>{{cite web|title=Lactose Intolerance|url=https://www.niddk.nih.gov/health-information/health-topics/digestive-diseases/lactose-intolerance/Pages/facts.aspx|website=NIDDK|access-date=25 October 2016|date=June 2014|url-status=live|archive-url=https://web.archive.org/web/20161025111752/https://www.niddk.nih.gov/health-information/health-topics/digestive-diseases/lactose-intolerance/Pages/facts.aspx|archive-date=25 October 2016}}</ref> Lactose intolerance does not cause damage to the [[gastrointestinal tract]].<ref name=Heyman2006>{{cite journal | vauthors = Heyman MB | s2cid = 2996092 | title = Lactose intolerance in infants, children, and adolescents | journal = Pediatrics | volume = 118 | issue = 3 | pages = 1279–86 | date = September 2006 | pmid = 16951027 | doi = 10.1542/peds.2006-1721 | doi-access = free }}</ref>

<!-- Cause -->
Lactose intolerance is due to the lack of the [[enzyme]] [[lactase]] in the [[small intestines]] to break lactose down into [[glucose]] and [[galactose]].<ref name=Stat2020>{{cite book |last1=Malik |first1=TF |last2=Panuganti |first2=KK |chapter=Lactose Intolerance |title=(StatPearls [Internet]) |publisher=StatPearls |date=January 2020 |pmid=30335318 |id=NBK532285 }}</ref> There are four types: primary, secondary, developmental, and congenital.<ref name=NIH2014Dig/> Primary lactose intolerance occurs as the amount of lactase declines as people grow up.<ref name=NIH2014Dig/> Secondary lactose intolerance is due to injury to the small intestine. Such injury could be the result of infection, [[celiac disease]], [[inflammatory bowel disease]], or other diseases.<ref name=NIH2014Dig/><ref name=BerniCananiPezzella2016>{{cite journal | vauthors = Berni Canani R, Pezzella V, Amoroso A, Cozzolino T, Di Scala C, Passariello A | title = Diagnosing and Treating Intolerance to Carbohydrates in Children | journal = Nutrients | volume = 8 | issue = 3 | pages = 157 | date = March 2016 | pmid = 26978392 | pmc = 4808885 | doi = 10.3390/nu8030157 | doi-access = free }}</ref> Developmental lactose intolerance may occur in [[premature babies]] and usually improves over a short period of time.<ref name=NIH2014Dig/> Congenital lactose intolerance is an extremely rare [[genetic disorder]] in which little or no lactase is made from birth.<ref name=NIH2014Dig/> The reduction of lactase production starts typically in late childhood or early adulthood,<ref name=NIH2014Dig/> but prevalence increases with age.

Non-digestion is not a disease ''by itself'', which even reduces total caloric intake if the microbiota do not convert it into absorbable nutrients. The symptoms are an effect of the fermentation sponsored by unabsorbed nutrients.  

<!-- Diagnosis and treatment -->
Diagnosis may be confirmed if symptoms resolve following eliminating lactose from the diet.<ref name=NIH2014Dig/> Other supporting tests include a [[hydrogen breath test]] and a [[stool acidity test]].<ref name=NIH2014Dig/> Other conditions that may produce similar symptoms include [[irritable bowel syndrome]], [[celiac disease]], and [[inflammatory bowel disease]].<ref name=NIH2014Dig/> Lactose intolerance is different from a [[milk allergy]].<ref name=NIH2014Dig/> Management is typically by decreasing the amount of lactose in the diet, taking [[lactase supplements]], or treating the underlying disease.<ref name=NIH2014Dig/><ref name=Vandenplas2015 /> People are typically able to drink at least one cup of milk without developing symptoms, with greater amounts tolerated if drunk with a meal or throughout the day.<ref name=NIH2014Dig/><ref name=SuchyBrannon2010>{{cite journal | vauthors = Suchy FJ, Brannon PM, Carpenter TO, Fernandez JR, Gilsanz V, Gould JB, Hall K, Hui SL, Lupton J, Mennella J, Miller NJ, Osganian SK, Sellmeyer DE, Wolf MA | title = NIH consensus development conference statement: Lactose intolerance and health | journal = NIH Consensus and State-Of-The-Science Statements | volume = 27 | issue = 2 | pages = 1–27 | date = February 2010 | pmid = 20186234 | url = https://consensus.nih.gov/2010/lactosestatement.htm | type = Consensus Development Conference, NIH. Review | archive-url = https://web.archive.org/web/20161218125118/https://consensus.nih.gov/2010/lactosestatement.htm | url-status = live | archive-date = 2016-12-18 }}</ref>

<!-- Epidemiology & History -->
Worldwide, around 65% of adults are affected by lactose malabsorption.<ref name=Bayless2017>{{cite journal | vauthors = Bayless TM, Brown E, Paige DM | s2cid = 2941077 | title = Lactase Non-persistence and Lactose Intolerance | journal = Current Gastroenterology Reports | volume = 19 | issue = 5 | pages = 23 | date = May 2017 | pmid = 28421381 | doi = 10.1007/s11894-017-0558-9 }}</ref> Other [[mammals]] usually lose the ability to digest lactose after [[weaning]]. Lactose intolerance is the [[ancestral state]] of all humans before the [[Recent human evolution|recent evolution]] of [[lactase persistence]] in some cultures, which extends lactose tolerance into adulthood.<ref name="Genetics of lactase persistence and"/> Lactase persistence evolved in several populations independently, probably as an adaptation to the [[domestication]] of [[dairy animals]] around 10,000 years ago.<ref>{{cite journal | vauthors = Ségurel L, Bon C | title = On the Evolution of Lactase Persistence in Humans | journal = Annual Review of Genomics and Human Genetics | volume = 18 | issue = 1 | pages = 297–319 | date = August 2017 | pmid = 28426286 | doi = 10.1146/annurev-genom-091416-035340 }}</ref><ref name="Lactose digestion and the evolution">{{cite journal | vauthors = Ingram CJ, Mulcare CA, Itan Y, Thomas MG, Swallow DM | s2cid = 3329285 | title = Lactose digestion and the evolutionary genetics of lactase persistence | journal = Human Genetics | volume = 124 | issue = 6 | pages = 579–91 | date = January 2009 | pmid = 19034520 | doi = 10.1007/s00439-008-0593-6 }}</ref> Today the prevalence of lactose tolerance varies widely between regions and ethnic groups. The ability to digest lactose is most common in people of Northern European descent, and to a lesser extent in some parts of [[Central Asia]], the [[Middle East]] and [[Africa]].<ref name=Bayless2017/> 

Lactose intolerance is most common among people of East Asian descent, with 90% lactose intolerance, people of Jewish descent, in many [[African countries]] and [[Arab countries]], and among people of Southern European descent (notably amongst Greeks and Italians). [[Traditional food]] cultures reflect local variations in tolerance and historically many societies have adapted to low levels of tolerance by making [[dairy product]]s that contain less lactose than fresh milk.<ref name="SilanikoveLeitner2015" /> One ethnographic example of this is ''[[kumis]]'', a fermented milk product that contains little to no lactose, which is the main source of dairy nutrition in [[Mongolia]].<ref>{{cite web |last1=Abdel-Salam |first1=Ahmed M. |last2=Al-Dekheil |first2=Ali |last3=Babkr |first3=Ali |last4=Farahna |first4=Mohammed |last5=Mousa |first5=Hassan M. |title=High fiber probiotic fermented mare's milk reduces the toxic effects of mercury in rats |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC3338224/ |website=North American Journal of Medical Sciences |pages=569–575 |doi=10.4297/najms.2010.2569 |date=December 2010 |quote="Fermentation destroys lactose in milk, converting it into lactic acid, ethanol, and carbon dioxide. This makes kumis acceptable for lactose intolerant people. Traditional kumis is prepared by mixing fermented milk with fresh raw mares’ milk."}}</ref>

The [[medicalization]] of lactose intolerance as a disorder has been attributed to biases in research history, since most early studies were conducted amongst populations which are normally tolerant,<ref name="Genetics of lactase persistence and"/> as well as the cultural and economic importance and impact of milk in countries such as the United States.<ref>{{cite journal |last1=Wiley |first1=Andrea S. |title="Drink Milk for Fitness": The Cultural Politics of Human Biological Variation and Milk Consumption in the United States |journal=American Anthropologist |date=2004 |volume=106 |issue=3 |pages=506–517 |doi=10.1525/aa.2004.106.3.506 |jstor=3567615 |doi-access=free }}</ref>

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