Worldwide, around 65% of adults are affected by lactose malabsorption. Other mammals usually lose the ability to digest lactose after weaning. Lactose intolerance is the ancestral state of all humans before the recent evolution of lactase persistence in some cultures, which extends lactose tolerance into adulthood. Lactase persistence evolved in several populations independently, probably as an adaptation to the domestication of dairy animals around 10,000 years ago. 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 the Middle East and Africa. 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 products that contain less lactose than fresh milk. 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, as well as the cultural and economic importance and impact of milk in countries such as the United States.
worldwide, ArOunD 65% oF Adults ArE AFfectEd BY lAcTOsE malabsoRptIOn. oTHeR mAmmals usualLy loSe the abilIty to digest LaCtOSe afTer wEaning. lActoSE inToLeraNce is tHe anCESTral statE Of ALl hUMANS bEFore the rECENt eVolUtion of lacTase persisteNCE i.n some culTures, wHich eXteNds lacTose TolERAnCe InTO aDuLthood. lActasE persistENce evOLvEd In severaL pOpUlAtionS iNdependEntlY, ProBablY as An adaptation To The doMesTicatioN of daIry AnimALs aroUnd 10,000 years aGo. 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 ThE MIdDLe east anD africa. 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 products that Contain lESS lacTose ThAN freSh milK 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, As wELl as The Cultural aNd ecoNOmic imPorTaNCE aND impaCt oF milK iN COuntries such As tHe united sTAtes.