Editing Lactose intolerance (section)

==History==
{{main|Lactase persistence}}
Greater lactose tolerance has come about in two ways.<ref name=Schnorr2016/> Some populations have developed genetic changes to allow the digestion of lactose: [[lactase persistence]].<ref name=Schnorr2016/> Other populations developed cooking methods like milk fermentation.<ref name=Schnorr2016>{{cite journal | vauthors = Schnorr SL, Sankaranarayanan K, Lewis CM, Warinner C | title = Insights into human evolution from ancient and contemporary microbiome studies | journal = Current Opinion in Genetics & Development | volume = 41 | pages = 14–26 | date = December 2016 | pmid = 27507098 | pmc = 5534492 | doi = 10.1016/j.gde.2016.07.003 }}</ref>

Lactase persistence in humans evolved relatively recently (in the last 10,000 years) among some populations. Around 8,000 years ago in modern-day Turkey, humans became reliant on newly-domesticated animals that could be milked; such as cows, sheep, and goats. This resulted in higher frequency of lactase persistence.<ref>{{Cite web|url=https://www.npr.org/sections/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance|title=An Evolutionary Whodunit: How Did Humans Develop Lactose Tolerance?|website=NPR.org|date=28 December 2012|access-date=2019-11-14|last1=Thompson|first1=Helen}}</ref> Lactase persistence became high in regions such as Europe, Scandinavia, the Middle East and Northwestern India. However, most people worldwide remain lactase {{em|non}}-persistent.<ref name="Genetics of lactase persistence and"/> Populations that raised animals not used for milk tend to have 90–100 percent of a lactose intolerant rate.<ref>{{Cite journal|last=Pray|first=W. Steven|date=2000|title=Lactose Intolerance: The Norm Among the World's Peoples|journal=American Journal of Pharmaceutical Education|volume=64|number=2|pages=205–207|url=http://archive.ajpe.org/legacy/pdfs/aj640216.pdf|id={{ProQuest|211177586}}|access-date=2019-11-20|archive-date=2021-04-30|archive-url=https://web.archive.org/web/20210430050702/http://archive.ajpe.org/legacy/pdfs/aj640216.pdf|url-status=dead}}</ref> For this reason, lactase persistence is of some interest to the fields of [[anthropology]], [[human genetics]], and [[archaeology]], which typically use the genetically derived persistence/non-persistence terminology.<ref>{{cite journal | vauthors = Curry A | s2cid = 4315860 | title = Archaeology: The milk revolution | journal = Nature | volume = 500 | issue = 7460 | pages = 20–2 | date = August 2013 | pmid = 23903732 | doi = 10.1038/500020a | bibcode = 2013Natur.500...20C | doi-access = free }}</ref>

The rise of dairy and producing dairy related products from cow milk alone, varies across different regions of the world, aside from genetic predisposition.<ref name="SilanikoveLeitner2015" /> The process of turning milk into cheese dates back earlier than 5200 BC.<ref>{{cite journal | vauthors = McClure SB, Magill C, Podrug E, Moore AM, Harper TK, Culleton BJ, Kennett DJ, Freeman KH | title = Fatty acid specific δ13C values reveal earliest Mediterranean cheese production 7,200 years ago | journal = PLOS ONE | volume = 13 | issue = 9 | pages = e0202807 | year = 2018 | pmid = 30183735 | pmc = 6124750 | doi = 10.1371/journal.pone.0202807 | bibcode = 2018PLoSO..1302807M | doi-access = free }}</ref>

DNA analysis in February 2012 revealed that [[Ötzi]] was lactose intolerant, supporting the theory that lactose intolerance was still common at that time, despite the increasing spread of agriculture and dairying.<ref>{{cite journal |vauthors=Keller A, Graefen A, Ball M, Matzas M, Boisguerin V, Maixner F, Leidinger P, Backes C, Khairat R, Forster M, Stade B, Franke A, Mayer J, Spangler J, McLaughlin S, Shah M, Lee C, Harkins TT, Sartori A, Moreno-Estrada A, Henn B, Sikora M, Semino O, Chiaroni J, Rootsi S, Myres NM, Cabrera VM, Underhill PA, Bustamante CD, Vigl EE, Samadelli M, Cipollini G, Haas J, Katus H, O'Connor BD, Carlson MR, Meder B, Blin N, Meese E, Pusch CM, Zink A |title=New insights into the Tyrolean Iceman's origin and phenotype as inferred by whole-genome sequencing |journal=Nat Commun |volume=3 |pages=698 |date=2012 |doi=10.1038/ncomms1701 |pmid=22426219|bibcode=2012NatCo...3..698K |s2cid=29041624 |doi-access=free }}</ref>

Genetic analysis shows lactase persistence has developed several times in different places independently in an example of [[convergent evolution]].<ref name=Tishkoff07>{{cite journal | vauthors = Tishkoff SA, Reed FA, Ranciaro A, Voight BF, Babbitt CC, Silverman JS, Powell K, Mortensen HM, Hirbo JB, Osman M, Ibrahim M, Omar SA, Lema G, Nyambo TB, Ghori J, Bumpstead S, Pritchard JK, Wray GA, Deloukas P | title = Convergent adaptation of human lactase persistence in Africa and Europe | journal = Nature Genetics | volume = 39 | issue = 1 | pages = 31–40 | date = January 2007 | pmid = 17159977 | pmc = 2672153 | doi = 10.1038/ng1946 }}</ref>

=== History of research ===
It was not until relatively recently that [[medicine]] recognised the worldwide prevalence of lactose intolerance and its genetic causes. Its symptoms were described as early as [[Hippocrates]] (460–370 BC),<ref>{{cite journal |author=Wilson J |title=Milk Intolerance: Lactose Intolerance and Cow's Milk Protein Allergy |journal=Newborn and Infant Nursing Reviews |date=December 2005 |volume=5 |issue=4 |pages=203–7 |doi=10.1053/j.nainr.2005.08.004}}</ref> but until the 1960s, the prevailing assumption was that tolerance was the norm. Intolerance was explained as the result of a milk allergy, intestinal pathogens, or as being [[psychosomatic]] – it being recognised that some cultures did not practice dairying, and people from those cultures often reacted badly to consuming milk.<ref name="pmid14044269">{{cite journal | vauthors = Auricchio S, Rubino A, Landolt M, Semenza G, Prader A | journal = Lancet | volume = 2 | issue = 7303 | pages = 324–6 | date = August 1963 | pmid = 14044269 | doi = 10.1016/s0140-6736(63)92991-x | title = Isolated Intestinal Lactase Deficiency in the Adult }}</ref><ref name="Simoons_1969">{{cite journal | vauthors = Simoons FJ | title = Primary adult lactose intolerance and the milking habit: a problem in biological and cultural interrelations. I. Review of the medical research | journal = The American Journal of Digestive Diseases | volume = 14 | issue = 12 | pages = 819–36 | date = December 1969 | pmid = 4902756 | doi = 10.1007/bf02233204 | s2cid = 22597839 }}</ref> Two reasons have been given for this misconception. One was that early research was conducted solely on European-descended populations, which have an unusually low incidence of lactose intolerance<ref name="Itan et al. 2010">{{cite journal | vauthors = Itan Y, Jones BL, Ingram CJ, Swallow DM, Thomas MG | title = A worldwide correlation of lactase persistence phenotype and genotypes | journal = BMC Evolutionary Biology | volume = 10 | pages = 36 | date = February 2010 | issue = 1 | pmid = 20144208 | pmc = 2834688 | doi = 10.1186/1471-2148-10-36 | doi-access = free | bibcode = 2010BMCEE..10...36I }}</ref> and an extensive cultural history of dairying. As a result, researchers wrongly concluded that tolerance was the global norm. Another reason is that lactose intolerance tends to be under-reported: lactose intolerant individuals can tolerate at least some lactose before they show symptoms, and their symptoms differ in severity. The large majority of people are able to digest some quantity of milk, for example in tea or coffee, without developing any adverse effects.<ref name="Savaiano and Levitt 1987">{{cite journal | vauthors = Savaiano DA, Levitt MD | title = Milk intolerance and microbe-containing dairy foods | journal = Journal of Dairy Science | volume = 70 | issue = 2 | pages = 397–406 | date = February 1987 | pmid = 3553256 | doi = 10.3168/jds.S0022-0302(87)80023-1 | doi-access=free | url=https://www.journalofdairyscience.org/article/S0022-0302(87)80023-1/abstract }}</ref> [[Fermented milk products|Fermented dairy products]], such as cheese, also contain significantly less lactose than plain milk. Therefore, in societies where tolerance is the norm, many lactose intolerant people who consume only small amounts of dairy, or have only mild symptoms, may be unaware that they cannot digest lactose.

Eventually, in the 1960s, it was recognised that lactose intolerance was correlated with [[race (classification of humans)|race]] in the United States.<ref name="pmid5953213">{{cite journal | vauthors = Bayless TM, Rosensweig NS | title = A racial difference in incidence of lactase deficiency. A survey of milk intolerance and lactase deficiency in healthy adult males | journal = JAMA | volume = 197 | issue = 12 | pages = 968–72 | date = September 1966 | pmid = 5953213 | doi = 10.1001/jama.1966.03110120074017 }}</ref><ref>{{cite journal |vauthors=Welsh JD, Rohrer V, Knudsen KB, Paustian FF | year = 1967 | title = Isolated Lactase Deficiency: Correlation of Laboratory Studies and Clinical Data | journal = Archives of Internal Medicine | volume = 120 | issue = 3 | pages = 261–269 | doi=10.1001/archinte.1967.00300030003003}}</ref><ref name="pmid5694356">{{cite journal | vauthors = Huang SS, Bayless TM | s2cid = 33249040 | title = Milk and lactose intolerance in healthy Orientals | journal = Science | volume = 160 | issue = 3823 | pages = 83–4 | date = April 1968 | pmid = 5694356 | doi = 10.1126/science.160.3823.83-a | bibcode = 1968Sci...160...83H }}</ref> Subsequent research revealed that lactose intolerance was more common globally than tolerance,<ref name="pmid4159716">{{cite journal | vauthors = Cook GC, Kajubi SK | title = Tribal incidence of lactase deficiency in Uganda | journal = Lancet | volume = 1 | issue = 7440 | pages = 725–9 | date = April 1966 | pmid = 4159716 | doi = 10.1016/s0140-6736(66)90888-9 }}</ref><ref>{{cite journal |vauthors=Jersky J, Kinsley RH | year = 1967 | title = Lactase Deficiency in the South African Bantu | journal = South African Medical Journal | volume = 41 | issue = 46 | pages = 1194–6 |pmid=6080167}}</ref><ref name="pmid5701921">{{cite journal | vauthors = Bolin TD, Crane GG, Davis AE | title = Lactose intolerance in various ethnic groups in South-East Asia | journal = Australasian Annals of Medicine | volume = 17 | issue = 4 | pages = 300–6 | date = November 1968 | pmid = 5701921 | doi =  10.1111/imj.1968.17.4.300}}</ref><ref name="pmid5818369">{{cite journal | vauthors = Flatz G, Saengudom C, Sanguanbhokhai T | s2cid = 4201371 | title = Lactose intolerance in Thailand | journal = Nature | volume = 221 | issue = 5182 | pages = 758–9 | date = February 1969 | pmid = 5818369 | doi = 10.1038/221758b0 | bibcode = 1969Natur.221..758F }}</ref><ref name="pmid6016903">{{cite journal | vauthors = Elliott RB, Maxwell GM, Vawser N | title = Lactose maldigestion in Australian Aboriginal children | journal = The Medical Journal of Australia | volume = 1 | issue = 2 | pages = 46–9 | date = January 1967 | pmid = 6016903 | doi =  10.5694/j.1326-5377.1967.tb21011.x| s2cid = 44475025 }}</ref> and that the variation was due to genetic differences, not an adaptation to cultural practices.<ref name="Simoons_1969" /><ref name="pmid5114667">{{cite journal | vauthors = Flatz G, Rotthauwe HW | title = Evidence against nutritional adaption of tolerance to lactose | journal = Humangenetik | volume = 13 | issue = 2 | pages = 118–25 | year = 1971 | pmid = 5114667 | doi = 10.1007/bf00295793 | s2cid = 33253438 }}</ref>