Lactose intolerance 56873 225785926 2008-07-15T11:45:42Z Neilbeach 295594 /* Hydrogen breath test */ {{Infobox_Disease | Name = Lactose intolerance | Image = Lactose(lac).png | Caption = [[Lactose]] ([[disaccharide]] of β-D-galactose & β-D-glucose) is normally split by [[lactase]]. | DiseasesDB = 7238 | ICD10 = {{ICD10|E|73||e|70}} | ICD9 = {{ICD9|271.3}} | ICDO = | Read Code = C313100 | OMIM = 223100 | OMIM_mult = {{OMIM2|150220}} | MedlinePlus = 000276 | eMedicineSubj = med | eMedicineTopic = 3429 | eMedicine_mult = {{eMedicine2|ped|1270}} | MeshID = D007787 }} '''Lactose intolerance''' is the inability to [[Metabolism|metabolize]] [[lactose]], a sugar found in [[milk]] and other [[dairy]] products, because the required enzyme [[lactase]] is absent in the intestinal system or its availability is lowered. Some people also mention pasteurized dairy products as a cause (raw milk contains small amounts of lactase). It is estimated that 20% of adult humans are lactose intolerant.<ref name="Kretchmer1">{{cite journal |author=Kretchmer N |title=Lactose and lactase--a historical perspective |journal=Gastroenterology |volume=61 |issue=6 |pages=805–13 |year=1971 |pmid=4947662 |doi=}}</ref> == Overview == [[disaccharide|Disaccharides]] cannot be absorbed through the wall of the small intestine into the bloodstream, so in the absence of [[lactase]], [[lactose]] present in ingested dairy products remains uncleaved and passes intact into the [[colon]]. The [[operon]]s of [[Gut flora|enteric bacteria]] quickly switch over to lactose [[metabolism]], and the resultant in vivo [[fermentation (biochemistry)|fermentation]] produces copious amounts of gas (a mixture of [[hydrogen]], [[carbon dioxide]], and [[methane]]). This, in turn, may cause a range of abdominal symptoms, including stomach [[cramp]]s, [[bloating]], and [[flatulence]]. In addition, as with other unabsorbed sugars (such as [[sorbitol]], [[mannitol]], and [[xylitol]]), the presence of lactose and its fermentation products raises the [[osmotic]] pressure of the [[colon (anatomy)|colon]] contents, thereby preventing the colon from reabsorbing water, and causing osmotic [[diarrhea]]. ==Classification== There are three major types of lactose intolerance:<ref name="Melvin">{{cite journal |author=Heyman MB |title=Lactose intolerance in infants, children, and adolescents |journal=Pediatrics |volume=118 |issue=3 |pages=1279–86 |year=2006 |pmid=16951027 |doi=10.1542/peds.2006-1721 |url=http://aappolicy.aappublications.org/cgi/content/full/pediatrics;118/3/1279}}</ref> #'''Primary lactose intolerance'''. Environmentally induced when weaning a child in non-dairy consuming societies.<ref name=variant/> This is found in many Asian and African cultures, where industrialized and commercial dairy products are uncommon. #'''Secondary lactose intolerance'''. Environmentally induced, resulting from certain [[gastrointestinal diseases]], including exposure to [[intestinal parasites]] such as [[giardia]].<ref name="Wiser">{{cite web |author=Mark Wiser |title=Intestinal Protozoa |url=http://www.tulane.edu/~wiser/protozoology/notes/intes.html |date=August 30, 2007 |publisher=Tulane University |accessdate=2008-01-31}}</ref><ref name="eMedicine">{{Emedicine|emerg|215|Giardiasis}} Andre Pennardt February 22, 2006</ref> In such cases the production of lactase may be permanently disrupted.<ref name="Wiser"/><ref name="eMedicine"/><ref>{{cite journal |author=Swagerty DL, Walling AD, Klein RM |title=Lactose intolerance |journal=Am Fam Physician |volume=65 |issue=9 |pages=1845–50 |year=2002 |pmid=12018807 |doi= |url=http://www.aafp.org/afp/20020501/1845.html}}</ref> A very common cause of '''temporary''' lactose intolerance is [[gastroenteritis]], particularly when the gastroenteritis is caused by [[rotavirus]]. Another form of temporary lactose intolerance is lactose overload in infants.<ref>[http://www.health-e-learning.com/articles/Lactose.pdf Colic and lactose intolerance]</ref> #'''Congenital lactase deficiency'''. A genetic disorder which prevents enzymatic production of lactase. Present at birth, and diagnosed in early infancy. == Lactase biology == The enzyme lactase, also called ''beta-D-galactosidase'', is synthesized if at least one of the two genes for it are present. Only when both gene expressions are affected is lactase enzyme synthesis reduced, which in turn reduces lactose digestion.<ref name=soy>[http://www.soynutrition.com/SoyHealth/SoyLactoseIntolerance.aspx Soy Nutrition]</ref>. Lactase persistence, allowing lactose digestion to proceed, is the [[dominant allele]]. Physiological lactose intolerance, therefore, is an [[autosomal recessive trait]]. However, cultures such as that of [[Japan]], where dairy consumption has been on the increase, demonstrate a lower prevalence of lactose intolerance in spite of a genetic predisposition<ref name="Yoshida">{{cite journal |author=Yoshida Y, Sasaki G, Goto S, Yanagiya S, Takashina K |title=Studies on the etiology of milk intolerance in Japanese adults |journal=Gastroenterol. Jpn. |volume=10 |issue=1 |pages=29–34 |year=1975 |pmid=1234085 |doi=}}</ref>. The normal [[mammal]]ian condition is for the young of a species to experience reduced [[lactase]] production at the end of the [[weaning]] period (a species-specific length of time). In non dairy consuming societies, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely. However, certain human populations have a [[mutation]] on [[chromosome]] 2 which results in a bypass of the common shutdown in lactase production, making it possible for members of these populations to continue consumption of fresh milk and other dairy products throughout their lives. Pathological lactose intolerance can be caused by [[Coeliac disease]], which damages the villi in the small intestine that produce lactase. This lactose intolerance is temporary. Lactose intolerance associated with coeliac disease ceases after the patient has been on a [[gluten-free diet]] long enough for the villi to recover{{Fact|date=October 2007}}. Certain people who report problems with consuming lactose are not actually lactose intolerant. In a study of 323 [[Sicily|Sicilian]] adults, Carroccio et al. (1998) found only 4% were both lactose intolerant and lactose maldigesters, while 32.2% were lactose maldigesters but did not test as lactose intolerant. However, Burgio et al. (1984) found that 72% of 100 Sicilians were lactose intolerant in their study and 106 of 208 northern Italians (i.e., 51%) were lactose intolerant. === Lactose intolerance by group === [[Image:LacIntol-World2.png|right|thumb|200px|Lactose Intolerance by Region (African countries are only a rough guess)]] {| class="wikitable sortable" | '''Human groups''' | '''Individuals Examined''' | '''Percent Intolerant''' | '''[[Allele frequency]]''' |- |[[Dutch people|Dutch]] || N/A || 1%<ref name=AdvHG>{{cite journal |author=Flatz G |title=Genetics of lactose digestion in humans |journal=Adv. Hum. Genet. |volume=16 |issue= |pages=1–77 |year=1987 |pmid=3105269 |doi=}}</ref> || N/A |- |[[Swedish people|Swedes]] || N/A || 2%<ref name=SA>{{cite journal |author=Kretchmer N |title=Lactose and lactase |journal=Sci. Am. |volume=227 |issue=4 |pages=71–8 |year=1972 |pmid=4672311 |doi=}}</ref> || 0.14 |- |[[Anglo-Celtic Australian|Europeans in Australia]] ||160 || 4%<ref name=SA/> || 0.20 |- |[[Northern Europeans]] and [[Scandinavians]]||5%<ref name=variant/><ref name=UCD/>||N/A |- |[[Danes]] || N/A || 5%<ref>{{cite web |author=Anne Charlotte Jäger |url=http://www.dskb.dk/index.jsp?id=7353&gr=7446 |title=Laktose-intolerans: Gentest for laktose-intolerans - hurtig og billig diagnostik |publisher=[[DSKB-NYT]] |date= 1, February 2006}}</ref> || N/A |- |[[Basque people|Basques]] || 85 || <10%<ref>{{cite web |author=N.S. Enattah et al. |url=http://www.ajhg.org/AJHG/fulltext/S0002-9297(07)61358-5 |title=Evidence of Still-Ongoing Convergence Evolution of the Lactase Persistence T-13910 Alleles in Humans |publisher=[[American Journal of Human Genetics]] |date= 1, September 2007}}</ref> || N/A |- |[[Demographics of the United Kingdom|British]]||N/A||5–15%<ref name=probiotic>{{cite journal |author=de Vrese M, Stegelmann A, Richter B, Fenselau S, Laue C, Schrezenmeir J |title=Probiotics--compensation for lactase insufficiency |journal=Am. J. Clin. Nutr. |volume=73 |issue=2 Suppl |pages=421S–429S |year=2001 |pmid=11157352 |doi= |url=http://www.ajcn.org/cgi/content/full/73/2/421S}}</ref> ||N/A |- |[[Swiss]] || N/A || 10%<ref name=SA/> || 0.316 |- |[[European Americans]] || 245 || 12%<ref name=SA/> || 0.346 |- |[[Tuareg]] || N/A || 13%<ref name=probiotic/> || N/A |- | [[Germans]] || N/A || 15%<ref name=probiotic/> || N/A |- | [[Austrians]] || N/A || 15–20%<ref name=probiotic/> || N/A |- |[[Eastern Slavs]] (Russians, Belarusians, Ukrainians) || N/A || 15%<ref>{{cite journal |author=Valenkevich LN, Iakhontova OI |title=[Prevalence of the lactase deficiency among the population of the northwestern region of Russia] |language=Russian |journal=Eksp Klin Gastroenterol |volume= |issue=1 |pages=97–100, 108 |year=2005 |pmid=15991859 |doi=}}</ref> || N/A |- |[[French people|Northern French]]||N/A||17%<ref name=probiotic/> ||N/A |- |[[Finnish people|Finn]]s || 134 || 18%<ref name=SA/> || 0.424 |- |Central [[Italian people|Italian]]s|| 65 || 19%<ref name=Italian/> ||N/A |- |[[Demographics of India|Indian]] Children||N/A||20%<ref name=variant>{{cite journal |author=Enattah NS, Sahi T, Savilahti E, Terwilliger JD, Peltonen L, Järvelä I |title=Identification of a variant associated with adult-type hypolactasia |journal=Nat. Genet. |volume=30 |issue=2 |pages=233–7 |year=2002 |pmid=11788828 |doi=10.1038/ng826}}</ref><ref name=UCD>{{cite web |title=Lactose Intolerance: The Molecular Explanation |url=http://nutrigenomics.ucdavis.edu/nutrigenomics/index.cfm?objectid=968814F6-65B3-C1E7-0C7007B71CC9959A |publisher=UC Davis Nutritional Genomics}}</ref> ||N/A |- |African [[Tutsi]] || N/A || 20%<ref name=SA/> || 0.447 |- |African [[Fulani]] || N/A || 23%<ref name=SA/> || 0.48 |- |[[Bedouin]]s || N/A||25%<ref name=probiotic/> ||N/A |- |Northern [[Demographics of India|Indians]] ||N/A||27%<ref name=Indian>{{cite journal |author=Tandon RK, Joshi YK, Singh DS, Narendranathan M, Balakrishnan V, Lal K |title=Lactose intolerance in North and South Indians |journal=Am. J. Clin. Nutr. |volume=34 |issue=5 |pages=943–6 |year=1981 |pmid=7234720 |doi= |url=http://www.ajcn.org/cgi/reprint/34/5/943}}</ref>||N/A |- | [[Portuguese people|Portuguese]] adults ||102||<35%<ref>http://users.med.up.pt/ruifonte/PDFs/2007-2008/Intol%20Lactose_2007_pag1-14.pdf</ref>||N/A |- |[[African American]] Children||N/A||45%<ref name=variant/>||N/A |- |[[Demographics of India|Indian]] Adults||150||50%<ref name=variant/><ref name=UCD/><ref>{{cite journal |author=Rana SV, Bhasin DK, Naik N |title=Lactose malabsorption in apparently healthy adults in northern India, assessed using lactose hydrogen breath test |journal=Indian J Gastroenterol |volume=23 |issue=2 |pages=78 |year=2004 |pmid=15176547 |doi= |url=http://www.indianjgastro.com/article.asp?issn=0254-8860;year=2004;volume=23;issue=2;spage=78;epage=78;aulast=Rana }}</ref>||N/A |- |Southern [[Italian people|Italian]]s|| 51 || 41%<ref name=Italian/> || N/A |- |[[Sami people|Saami]] (in [[Russia]] and [[Finland]]) || N/A || 25–60%<ref>{{cite journal |author=Kozlov A, Lisitsyn D |title=Hypolactasia in Saami subpopulations of Russia and Finland |journal=Anthropol Anz |volume=55 |issue=3-4 |pages=281–7 |year=1997 |pmid=9468755 |doi=}}</ref> || N/A |- |Northern [[Italian people|Italian]]s|| 89 || 52%<ref name=Italian>{{cite journal |author=Cavalli-Sforza LT, Strata A, Barone A, Cucurachi L |title=Primary adult lactose malabsorption in Italy: regional differences in prevalence and relationship to lactose intolerance and milk consumption |journal=Am. J. Clin. Nutr. |volume=45 |issue=4 |pages=748–54 |year=1987 |pmid=3565303 |doi= |url=http://www.ajcn.org/cgi/reprint/45/4/748.pdf |format=PDF}}</ref> || N/A |- |North American [[Hispanic]]s ||N/A||53%<ref name=probiotic/> ||N/A |- |[[Balkans]]|| N/A||55%<ref name=probiotic/> ||N/A |- |[[Mexican American]] Males||N/A||55%<ref name=variant/><ref name=UCD/>||N/A |- |[[Cretans]]||N/A||56%<ref name=variant/>||N/A |- |African [[Maasai]] || 21 || 62%<ref>{{cite journal |author=Jackson RT, Latham MC |title=Lactose malabsorption among Masai children of East Africa |journal=Am. J. Clin. Nutr. |volume=32 |issue=4 |pages=779–82 |year=1979 |pmid=581925 |doi=}}</ref> || N/A |- | [[French people|Southern French]]||N/A||65%<ref name=probiotic/> ||N/A |- |[[Greek Cypriots]]||N/A||66%<ref name=variant/><ref name=UCD/>||N/A |- |[[American Jews|North American Jews]]||N/A||68.8%<ref name=variant/><ref name=UCD/>||N/A |- |Southern [[Demographics of India|Indians]] ||N/A||70%<ref name=Indian/>||N/A |- |[[Sicily#People|Sicilians]] ||100||71%<ref name=Burgio>{{cite journal |author=Burgio GR, Flatz G, Barbera C, ''et al'' |title=Prevalence of primary adult lactose malabsorption and awareness of milk intolerance in Italy |journal=Am. J. Clin. Nutr. |volume=39 |issue=1 |pages=100–4 |year=1984 |pmid=6691285 |doi= |url=http://www.ajcn.org/cgi/reprint/39/1/100.pdf |format=PDF}}</ref><ref>{{cite journal |author=Vesa TH, Marteau P, Korpela R |title=Lactose intolerance |journal=J Am Coll Nutr |volume=19 |issue=2 Suppl |pages=165S–175S |year=2000 |pmid=10759141 |doi= |url=http://www.jacn.org/cgi/content/full/19/suppl_2/165S}}</ref>||N/A |- |[[South American]]s||N/A||65–75%<ref name=probiotic/> ||N/A |- |Rural [[Mexican]]s||N/A||73.8%<ref name=variant/><ref name=UCD/>||N/A |- |[[African American]]s || 20 || 75%<ref name=SA/> || 0.87 |- |[[Kazakh]]s from northwest [[Xinjiang]] || 195 || 76.4% <ref name=China/>|| |- |[[Demographics of Lebanon|Lebanese]]||75||78%<ref>{{cite journal |author=Nasrallah SM |title=Lactose intolerance in the Lebanese population and in "Mediterranean lymphoma" |journal=Am. J. Clin. Nutr. |volume=32 |issue=10 |pages=1994–6 |year=1979 |pmid=484518 |doi= |url=http://www.ajcn.org/cgi/reprint/32/10/1994.pdf |format=PDF}}</ref>||N/A |- |[[Central Asia]]ns||N/A||80%<ref name=probiotic/> ||N/A |- |[[Alaska Natives|Alaskan Eskimo]]||N/A||80%<ref name=variant/><ref name=UCD/>||N/A |- |[[Australian Aborigine]]s || 44 || 85%<ref name=SA/> || 0.922 |- |[[Inner Mongolia]]ns||198||87.9%<ref name=China>{{cite journal |author=Wang YG, Yan YS, Xu JJ, ''et al'' |title=Prevalence of primary adult lactose malabsorption in three populations of northern China |journal=Hum. Genet. |volume=67 |issue=1 |pages=103–6 |year=1984 |pmid=6235167 |doi=}}</ref>|| |- |African [[Bantu]] || 59 || 89%<ref name=SA/> || 0.943 |- |[[Asian American]]s||N/A||90%<ref name=variant/><ref name=UCD/>||N/A |- |Northeastern [[Han Chinese]] || 248 || 92.3%<ref name=China/>|| |- |[[Chinese people|Chinese]] || 71 || 93%<ref name=SA/> || 0.964 |- |[[Southeast Asian]]s||N/A||98%<ref name=variant/><ref name=UCD/>||N/A |- |[[Thai people|Thai]]s || 134 || 98%<ref name=SA/> || 0.99 |- |[[Native Americans in the United States|Native American]]s || 24 || 100%<ref name=SA/> || 1.00 |} The [[statistical significance]] varies greatly depending on number of people sampled. Lactose intolerance levels also increase with age. At ages 2 - 3 yrs., 6 yrs., and 9 - 10 yrs., the amount of lactose intolerance is, respectively: * 6% to 15% in white Americans and northern Europeans * 18%, 30%, and 47% in [[Mexican American]]s * 25%, 45%, and 60% in black [[South African]]s * approximately 30%, 80%, and 85% in Chinese and Japanese * 30–55%, 90%, and >90% in [[Mestizo]]s of [[Peru]]<ref name=Sahi>{{cite journal |author=Sahi T |title=Genetics and epidemiology of adult-type hypolactasia |journal=Scand. J. Gastroenterol. Suppl. |volume=202 |issue= |pages=7–20 |year=1994 |pmid=8042019 |doi=}}</ref><ref>{{cite journal |author=Woteki CE, Weser E, Young EA |title=Lactose malabsorption in Mexican-American children |journal=Am. J. Clin. Nutr. |volume=29 |issue=1 |pages=19–24 |year=1976 |pmid=946157 |doi= |url=http://www.ajcn.org/cgi/reprint/29/1/19.pdf |format=PDF}}</ref> [[Chinese people|Chinese]] and [[Japanese people|Japanese]] populations typically lose between 80 and 90 percent of their ability to digest lactose within three to four years of weaning. Most Japanese can consume 200 ml (8 fl oz) of milk without severe symptoms (McGee 2004; Swagerty et al, 2002).<ref name ="Yoshida"/> [[Ashkenazi Jew]]s can keep 20 - 30 percent of their ability to digest lactose for many years.<ref name=Sahi/> <ref>{{cite journal |author=Flatz G |title=Genetics of lactose digestion in humans |journal=Adv. Hum. Genet. |volume=16 |issue= |pages=1–77 |year=1987 |pmid=3105269 |doi=}}</ref><ref>{{cite journal |author=Swallow DM |title=Genetics of lactase persistence and lactose intolerance |journal=Annu. Rev. Genet. |volume=37 |issue= |pages=197–219 |year=2003 |pmid=14616060 |doi=10.1146/annurev.genet.37.110801.143820}}</ref> Of the 10% of the Northern European population that develops lactose intolerance, the development of lactose intolerance is a gradual process spread out over as many as 20 years.<ref>{{cite journal |author=Matthews SB, Waud JP, Roberts AG, Campbell AK |title=Systemic lactose intolerance: a new perspective on an old problem |journal=Postgrad Med J |volume=81 |issue=953 |pages=167–73 |year=2005 |pmid=15749792 |doi=10.1136/pgmj.2004.025551}}</ref> == Diagnosis == To assess lactose intolerance, the intestinal function is challenged by ingesting more dairy than can be readily digested. Clinical symptoms typically appear within 30 minutes but may take up to 1-2 hours depending on other foods and activities.<ref>{{cite web |author=R. Bowen |title=Lactose Intolerance (Lactase Non-Persistence) |url=http://www.vivo.colostate.edu/hbooks/pathphys/digestion/smallgut/lactose_intol.html |date=December 28, 2006 |publisher=Colorado State University |work=Pathophysiology of the Digestive System}}</ref> Substantial variability of the clinical response (symptoms of nausea, cramping, bloating, diarrhea, and flatulence) are to be expected as the extent and severity of lactose intolerance varies between individuals. When considering the need for confirmation, it is important to distinguish lactose intolerance from [[milk allergy]], which is an abnormal [[immune response]] (usually) to milk proteins. Since lactose intolerance is the normal state for most adults on a worldwide scale, and not considered a disease condition, a medical diagnosis is not normally required. However, if confirmation is necessary, three tests are available: === Hydrogen breath test === In a [[hydrogen breath test]], after an overnight fast, 50 [[gram]]s of lactose (in a solution with water) are swallowed. If the lactose cannot be digested, enteric bacteria metabolize it and produce [[hydrogen]]. This can be detected in the patient's breath by a clinical gas chromatograph or a compact solid state detector. The test takes about 2 to 3 hours. A medical condition with similar symptoms is [[fructose malabsorption]]. In conjunction, measuring the blood glucose level every 10 - 15 minutes after ingestion will show a "flat curve" in individuals with lactose malabsorption, while the lactase persistent will have a significant "top", with an elevation of typically 50 to 100% within 1 - 2 hours. However, given the need for frequent blood drawns, this approach has been largely supplanted by breath testing. === Stool acidity === Can be used to diagnose lactose intolerance in small infants, for whom other forms of testing are risky or impractical.<ref>{{cite web |author=National Digestive Diseases Information Clearinghouse |title=Lactose Intolerance -- How is lactose intolerance diagnosed? |url=http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/#diagnosed |date=March 2006 |publisher= National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health}}</ref> === Intestinal biopsy === An intestinal biopsy can confirm lactose intolerance following discovery of elevated hydrogen in the hydrogen breath test.<ref name="Berdanier">{{cite book |author=Hargrove, James L.; Berdanier, Carolyn D. |title=Nutrition and gene expression |publisher=CRC Press |location=Boca Raton |year=1993 |pages= |isbn=0-8493-6961-4 |oclc= |doi=}}</ref>. However, given the invasive nature of this test, and the need for a highly specialized laboratory to measure lactase enzymes or mRNA in the biposy tissue, this approach is used almost exclusively in clinical research. === History of diagnosis === The [[ancient Greece|ancient Greek]] physician [[Hippocrates]] (460-370 B.C.) first noted gastrointestinal upset and skin problems in some who consumed milk;<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> patients experiencing the former symptom may likely have been suffering from lactose intolerance. However, it was only in the last few decades that the syndrome was more widely described by modern medical science. The condition was first recognized in the 1950s and 1960s when various organizations like the [[United Nations]] began to engage in systematic [[famine]]-relief efforts in countries outside Europe for the first time. Holzel et al (1959) and Durand (1959) produced two of the earliest studies of lactose intolerance. As anecdotes of embarrassing dairy-induced discomfort increased, the [[First World]] donor countries could no longer ascribe the reports to spoilage in transit or inappropriate food preparation by the [[Third World]] recipients. Because the first nations to industrialize and develop modern scientific [[medicine]] were dominated by people of European descent, adult dairy consumption was long taken for granted. Westerners for some time did not recognize that the majority of the human ethno-genetic groups could not consume dairy products during adulthood. Although there had been regular contact between Europeans and non-Europeans throughout history, the notion that large-scale medical studies should be representative of the ethnic diversity of the human populations (as well as all genders and ages) did not become well-established until after the [[American Civil Rights Movement (1955-1968)|American Civil Rights Movement]]. Since then, the relationship between lactase and lactose has been thoroughly investigated in [[food science]] due to the growing market for dairy products among non-Europeans. Originally it was [[hypothesis]]ed that gut bacteria such as [[E. coli]] produced the [[lactase]] enzyme needed to cleave lactose into its constituent [[monosaccharide]]s and thus become metabolisable and digestible by humans. Some form of human-bacteria [[symbiosis]] was proposed as a means of producing lactase in the human digestive tract. Genetics and protein analysis techniques by the early 1970s revealed this to be untrue; humans produce their own lactase enzyme natively in intestine cells.{{Fact|date=January 2008}} According to Heyman (2006), approximately 70% of the global population cannot tolerate lactose in adulthood. Thus, some argue that the terminology should be reversed — lactose intolerance should be seen as the norm, and the minority groups should be labeled as having ''lactase persistence''. A counter argument to this is that the cultures that don't generally consume unmodified milk products have little need to discuss their intolerance to it, leaving the cultures for which lactose intolerance is a significant dietary issue to define its terminology. == History of genetic prevalence == Lactose intolerance has been studied as an aid in understanding ancient diets and population movement in prehistoric societies. Milking an animal vastly increases the calories that may be extracted from the animal as compared to the consumption of its meat alone. It is not surprising then, that consuming milk products became an important part of the agricultural way of life in the [[Neolithic]]. It is believed that most of the milk was used to make mature [[cheese]]s which are mostly lactose free.{{Fact|date=October 2007}} Roman authors recorded that the people of northern Europe, particularly [[Roman Britain|Britain]] and [[Germanic peoples|Germany]] drank unprocessed milk (as opposed to the Romans who made [[cheese]]).{{Fact|date=February 2007}} This corresponds very closely with modern European distributions of lactose intolerance, where the people of [[United Kingdom|Britain]], [[Germany]] and [[Scandinavia]] have a good tolerance, and those of southern Europe, especially [[Italy]], have a poorer tolerance.<ref>{{cite web |title=Lactose tolerance/intolerance |url=http://www.gnxp.com/MT2/archives/001681.html |date=January 19, 2004 |publisher=Gene Expression |accessdate=2008-01-31}}</ref> In east Asia, historical sources also attest that the [[China|Chinese]] did not consume milk, whereas the nomads that lived on the borders did. Again, this reflects modern distributions of intolerance. China is particularly notable as a place of poor tolerance, whereas in [[Mongolia]] and the [[Steppe|Asian steppes]] horse milk is drunk regularly. This tolerance is thought to be advantageous as the nomads do not settle down long enough to process mature cheese. Given that their prime source of income is generated through horses, to ignore their milk as a source of calories would be greatly detrimental. The nomads also make an alcoholic beverage, called [[Kumis]], from horse milk, although the [[fermentation (food)|fermentation]] process reduces the amount of lactose present. The [[Fulani Empire|African Fulani]] have a nomadic origin and their culture once completely revolved around cow, goat, and sheep herding. [[Dairy]] products were once a large source of nutrition for them. As might be expected if lactase persistence evolved in response to dairy product consumption, they are particularly tolerant to lactose (about 77% of the population). Many Fulani live in [[Guinea-Conakry]], [[Burkina Faso]], [[Mali]], [[Nigeria]], [[Niger]], [[Cameroon]], and [[Chad]]. There is some debate on exactly where and when genetic mutation(s) occurred. Some argue for separate mutation events in [[Sweden]] (which has one of the lowest levels of lactose intolerance in the world) and the Arabian Peninsula around 4000 BC. However, others argue for a single mutation event in the Middle East at about 4500 BC which then subsequently radiated. Some sources suggest a third and more recent mutation in the East African [[Tutsi]]. Whatever the precise origin in time and place, most modern [[Northern Europe]]ans and people of European ancestry show the effects of this mutation (that is, they are able to safely consume milk products all their lives) while most modern [[East Asia]]ns, [[sub-Saharan Africa]]ns and native peoples of the Americas and [[Pacific Islands]] do not (making them lactose intolerant as adults).{{fact|date=January 2008}}<!-- previously http://us.cambridge.org/Books/kiple/lactose.htm which is now a deadlink and 8 books listed by Kiple - which one ? --> The [[Maasai]] ability to consume dairy without exhibiting symptoms may be due to a different genetic mutation.<ref>{{cite news |author=Swaminathan, Nikhil |title=African Adaptation to Digesting Milk Is "Strongest Signal of Selection Ever" |url=http://www.sciam.com/article.cfm?articleID=727EA883-E7F2-99DF-36D89AB12E930315&sc=I100322 |date=December 11, 2006 |journal=Scientific American}}</ref> Or it may be due to the fact that they curdle their milk before they consume it, removing the lactose. A thorough scientific overview of genetic polymorphisms of intestinal lactase activity in adult hypolactasia, is in chapter 76 of OMMBID.<ref> [[Charles Scriver]], Beaudet, A.L., Valle, D., Sly, W.S., Vogelstein, B., Childs, B., Kinzler, K.W. (Accessed 2007). [http://www.ommbid.com The Online Metabolic and Molecular Bases of Inherited Disease]. New York: McGraw-Hill. - Summaries of 255 chapters, full text through many universities. There is also the [http://books.mcgraw-hill.com/medical/ommbid/blog/ OMMBID blog]. </ref> A noncoding variation in the MCM6 gene has been strongly associated with adult type hypolactasia.<ref>{{cite journal |author=Enattah NS, Sahi T, Savilahti E, Terwilliger JD, Peltonen L, Järvelä I |title=Identification of a variant associated with adult-type hypolactasia |journal=Nat. Genet. |volume=30 |issue=2 |pages=233–7 |year=2002 |pmid=11788828 |doi=10.1038/ng826}}</ref> == Managing lactose intolerance == For persons living in societies where the diet contains relatively little dairy, lactose intolerance is not considered a condition that requires treatment. However, those living among societies that are largely lactose-tolerant may find lactose intolerance troublesome. Although there are still no methodologies to reinstate lactase production, some individuals have reported their intolerance to vary over time (depending on health status and pregnancy<ref name:"Roy"> {{Emedicine|med|3429|Lactose Intolerance}} Roy, Barakat, Nwakakwa, Shojamanesh, Khurana, July 5, 2006 - About 44% of lactose intolerant women regain the ability to digest lactose during pregnancy. This might be caused by slow intestinal transit and intestinal flora changes during pregnancy.</ref>). Lactose intolerance is not usually an all-or-nothing condition: the reduction in lactase production, and hence, the amount of lactose that can be tolerated varies from person to person. Since lactose intolerance poses no further threat to a person's health, managing the condition consists in minimizing the occurrence and severity of symptoms. Berdanier and Hargrove recognise 4 general principles: 1) avoidance of dietary lactose; 2) substitution to maintain nutrient intake; 3) regulation of calcium intake; 4) use of enzyme substitute. === Avoiding lactose-containing products === Since each individual's tolerance to lactose varies, according to the US [[National Institute of Health]], "Dietary control of lactose intolerance depends on people learning through trial and error how much lactose they can handle."<ref name=NDDIC>{{cite web |author=National Digestive Diseases Information Clearinghouse |title=Lactose Intolerance |url=http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/ |date=March 2006 |publisher=National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health}}</ref> Label reading is essential as commercial terminology varies according to language and region.<ref name="Berdanier"/> Lactose is present in 2 large food categories: Conventional dairy products, and as a food additive (in dairy and non dairy products). ==== Dairy products ==== Lactose is a water soluble molecule. Therefore fat percentage and the [[curd]]ling process have an impact on which foods may be tolerated. In the [[curd]]ling process lactose is found in the water portion along with [[whey]] and [[casein]], but is not found in the fat portion. Dairy products which are "fat reduced" or "fat free" generally have a slightly higher lactose percentage. Additionally, [[diet food|low fat]] dairy foods also often have various dairy derivatives such as [[milk solids]] added to them to enhance sweetness, increasing the lactose content. '''Milk'''. [[Human milk]] has the highest lactose percentage at around 9%. Unprocessed cow milk has 4.7% lactose. Unprocessed milk from other mammals contains similar lactose percentages ([[goat milk]] 4.1%,<ref>[http://www.goatworld.com/articles/goatmilk/colostrum.shtml Composition of Human, Cow, and Goat Milks - Goat Milk - GOATWORLD.COM<!-- Bot generated title -->]</ref> [[Bovinae|buffalo]] 4.86%,<ref name="Peeva">{{cite journal |author=Peeva |title=Composition of buffalo milk. Sources of specific effects on the separate components |year=2001 |journal=Bulg. J. Agric. Sci. |volume=7 |pages=329–35 |url=http://bjas.hit.bg/07/693A.htm}}</ref> [[yak]] 4.93%,<ref>[http://jag.igr.poznan.pl/2004-Volume-45/2/pdf/2004_Volume_45_2-215-224.pdf C:\JAG2\Jiang.vp<!-- Bot generated title -->]</ref> [[sheep milk]] 4.6%) '''Butter'''. The butter making process separates milk's water components from the fat components. Lactose, being a water soluble molecule, will not be present in the butter unless milk solids are added to the ingredients. '''Yogurt''' and [[kefir]]. People can be more tolerant of traditionally made [[yogurt]] than milk because it contains lactase enzyme produced by the bacterial cultures used to make the yogurt. However, many commercial brands contain milk solids, increasing the lactose content. '''Cheeses'''. Traditionally made hard cheese (such as [[Swiss cheese]]) and soft ripened cheeses may create less reaction than the equivalent amount of milk because of the processes involved. [[Fermentation]] and higher fat content contribute to lesser amounts of lactose. Traditionally made Swiss or [[Cheddar cheese|Cheddar]] might contain 10% of the lactose found in whole [[milk]]. In addition, the traditional aging methods of cheese (over 2 years) reduces their lactose content to practically nothing.[http://www.ilovecheese.com/lactose_intolerant_faqs.asp] Commercial cheese brands, however, are generally manufactured by modern processes that do not have the same lactose reducing properties, and as no regulations mandate what qualifies as an "aged" cheese, this description does not provide any indication of whether the process used significantly reduced lactose. '''Buttermilk''', '''sour cream''' and '''ice cream''', like yogurt, if made the traditional way, will generally be quite tolerable, but most modern brands add milk solids.<ref>{{cite web |author=Dairy Science and Technology, Dept. of Food Science |title=Ice Cream Formulations |url=http://www.foodsci.uoguelph.ca/dairyedu/icform.html |publisher=University of Guelph}}</ref> Consult labels.<ref>{{cite journal |author=Reger, Combs, Coulter and Koch |title=A Comparison of Dry Sweet Cream Buttermilk and Non-Fat Dry Milk Solids in Breadmaking |url=http://jds.fass.org/cgi/content/abstract/34/2/136 |journal=Journal of Dairy Science |volume=34 |issue= 2 |pages=136–44}}</ref> '''Examples of lactose levels in foods'''. As scientific consensus has not been reached concerning lactose percentage analysis methods <ref>[http://drinc.ucdavis.edu/goat1.htm Goat Milk Composition]</ref> (non-hydrated form or the mono-hydrated form), and considering that dairy content varies greatly according to labeling practices, geography and manufacturing processes, lactose numbers may not be very reliable. The following are examples of lactose levels in foods which commonly set off symptoms.<ref name=NDDIC/> These quantities are to be treated as guidelines only. :{| border=1 cellspacing=0 cellpadding=5 ! Dairy product !!Lactose Content |- |Yogurt, plain, low-fat, 240 mL | align="right" | 5 g&nbsp;&nbsp; |- |Milk, reduced fat, 240 mL |align="right" | 11 g&nbsp;&nbsp; |- |Swiss cheese, 28 g |align="right" | 1 g&nbsp;&nbsp; |- |Ice cream, 120 mL |align="right" | 6 g&nbsp;&nbsp; |- |Cottage cheese, 120 mL |align="right" | 2–3 g&nbsp;&nbsp; |- |} ==== Lactose in non-dairy products ==== Lactose (also present when labels state [[lactoserum]], [[whey]], [[milk solids]], [[modified milk ingredients]], etc) is a commercial [[food additive]] used for its texture, flavor and adhesive qualities, and is found in foods such as processed meats<ref name="OHSU">{{cite web |title=General guidelines for milk allergy |url=http://www.ohsu.edu/health/health-topics/topic.cfm?id=10182 |publisher=Oregon Health & Science University}}</ref> ([[sausage]]s/[[hot dog]]s, sliced meats, [[Pâté]]s), gravy stock powder, [[margarine]]s<ref>{{cite web |title=Margarine Regulations |url=http://www.gov.ns.ca/JUST/REGULATIONS/regs/marge.htm}}</ref>, sliced [[bread]]s,<ref>{{cite web |title=Enriched White Bread in Canada |url=http://www.celiac.ca/Articles/PAB%20Enriching%20GF%20Foods.html |publisher=The Canadian Celiac Association}}</ref><ref>{{cite journal |title=Influence of Nonfat Dry Milk Solids on the Nutritive Value of Bread |url=http://jds.fass.org/cgi/content/abstract/29/12/821 |journal=Journal of Dairy Science |date= |volume=29 |issue=12 |pages=821–9}}</ref> breakfast cereals,<ref name="OHSU" /ref> [[potato chip]]s,<ref name="Bartek">{{cite web |title=Bartek, food additive company |url=http://www.bartek.ca/pdfs/Applications/SavouryProducts/SavourySnackFoods/Savoury%20Snack%20Foods%20Alphabetical%20List%20of%20Product%20Names.pdf |format=PDF}}</ref> dried [[fruit]], [[Food processing|processed foods]], [[medication]]s, preprepared meals, meal replacement (powders and bars), protein supplements (powders and bars). [[Kosher]] products labeled ''[[pareve]]'' are free of milk. However, if a "D" (for "Dairy) is present next to the circled "K," "U," or other [[hechsher]], the food likely contains milk solids<ref name="OHSU"/> (although it may also simply indicate that the product was produced on equipment shared with other products containing milk derivatives). ==== Alternative products ==== '''Milk.''' The [[dairy industry]] has created quality low-lactose or lactose-free products to replace regular dairy. Lactose-free milk can be produced by passing milk over lactase enzyme bound to an inert carrier: once the molecule is cleaved, there are no lactose ill-effects. A form is available with reduced amounts of lactose (typically 30% of normal), and alternatively with nearly 0%. [[Finland]] has had "HYLA" (acronym for ''hydrolysed lactose'') products available for many years, even though the number of lactose intolerant people there is relatively small. These low-lactose level cow's milk products, ranging from ice cream to cheese, use a [[Valio]] patented chromatographic separation method to remove lactose. The ultra-pasteurization process, combined with aseptic packaging, ensures a long shelf-life. Recently, the range of low-lactose products available in Finland has been augmented with milk and other dairy products (such as ice cream, butter, and buttermilk) that contain no lactose at all. The remaining about 20% of lactose in HYLA products is taken care of enzymatically. These typically cost 2 - 4 times more than equivalent products containing lactose. Valio also markets these products in [[Sweden]]. Alternatively, a bacterium such as ''L. acidophilus'' may be added, which affects the lactose in milk the same way it affects the lactose in [[yogurt]] (see above). '''[[Plant milk|Plant based milks]]''' and derivatives are the only ones to be 100% lactose free ([[soy milk]], [[almond milk]], [[oat milk]], [[rice milk]], [[peanut milk]]). === Lactase supplementation === When lactose avoidance is not possible, or on occasions when a person chooses to consume such items, then enzymatic [[lactase]] supplements may be used.<ref name="Montalto">{{cite journal |author=Montalto M, Curigliano V, Santoro L, ''et al'' |title=Management and treatment of lactose malabsorption |journal=World J. Gastroenterol. |volume=12 |issue=2 |pages=187–91 |year=2006 |pmid=16482616 |doi= |url=http://www.wjgnet.com/1007-9327/12/187.asp}}</ref><ref>{{cite journal |author=He M, Yang Y, Bian L, Cui H |title=[Effect of exogenous lactase on the absorption of lactose and its intolerance symptoms] |language=Chinese |journal=Wei Sheng Yan Jiu |volume=28 |issue=5 |pages=309–11 |year=1999 |pmid=12712706 |doi=}}</ref> Lactase enzymes similar to those produced in the small intestines of humans are produced industrially by [[fungi]] of the [[genus]] ''[[aspergillus]]''. The enzyme, β-galactosidase, is available in tablet form in a variety of doses, in many countries without a prescription. It functions well only in high-acid environments, such as that found in the human gut due to the addition of gastric juices from the stomach. Unfortunately, too much acid can denature it,<ref>{{cite journal |author=O'Connell S, Walsh G |title=Physicochemical characteristics of commercial lactases relevant to their application in the alleviation of lactose intolerance |journal=Appl. Biochem. Biotechnol. |volume=134 |issue=2 |pages=179–91 |year=2006 |pmid=16943638| doi = 10.1385/ABAB:134:2:179 <!--Retrieved from CrossRef by DOI bot-->}}</ref> and it therefore should not be taken on an empty stomach. Also, the enzyme is ineffective if it does not reach the small intestine by the time the problematic food does. Lactose-sensitive individuals should experiment with both timing and dosage to fit their particular need. But supplements such as these may not be able to provide the accurate amount of [[lactase]] needed{{Fact|date=October 2007}} to adequately digest the [[lactose]] contained in dairy products, which may lead to symptoms similar to the existing lactose intolerance. While essentially the same process as normal intestinal lactose digestion, direct treatment of milk employs a different variety of industrially produced lactase. This enzyme, produced by [[yeast]] from the genus ''[[kluyveromyces]]'', takes much longer to act, must be thoroughly mixed throughout the product, and is destroyed by even mildly acidic environments. It therefore has been much less popular as a consumer product{{Fact|date=October 2007}} (sold, where available, as a liquid) than the ''aspergillus''-produced tablets, despite its predictable effectiveness. Its main use is in producing the lactose-free or lactose-reduced dairy products sold in supermarkets. Enzymatic lactase supplementation may have an advantage over avoiding dairy products, in that alternative provision does not need to be made to provide sufficient calcium intake, especially in children.<ref>{{cite journal |author=Heyman MB |title=Lactose intolerance in infants, children, and adolescents |journal=Pediatrics |volume=118 |issue=3 |pages=1279–86 |year=2006 |pmid=16951027 |doi=10.1542/peds.2006-1721 |url=http://pediatrics.aappublications.org/cgi/content/full/118/3/1279}}</ref> ===Rehabituation to dairy products=== ::''Wiktionary has an entry for [[wikt:habituation|rehabituation]].'' For healthy individuals with Secondary lactose intolerance, it may be possible to train bacteria in the large intestine to break down lactose more effectively[http://www.agriculture.purdue.edu/agricultures/past/Spring1998/1998-Spring-Spotlights.pdf] by consuming small quantities of dairy products several times a day over a couple of weeks. Reintroducing dairy in this way to people who have an underlying or chronic illness, however, is not recommended, as certain illnesses damage the [[intestinal tract]] in a way which prevents the [[lactase]] enzyme from being expressed. However, other studies have shown that [[lactase]] production does not seem to be induced by dairy/lactose consumption.[http://www.foodreactions.org/intolerance/lactose/prevalence.html] == Nutritional concerns == === Primary lactose intolerance === Populations where primary lactose intolerance is the norm have demonstrated similar health levels to westerners (outside of malnutrition issues; see the [[#History of genetic prevalence|History of genetic prevalence]] subsection above) or better health ([[Japan]]). === Secondary lactose intolerance === While secondary lactose intolerance does not inherently affect an individual's nutritional needs, according to mainstream media and "accepted" doctrines in western European and North American countries, dairy is an essential part of a healthy diet. Dairy products are relatively good and accessible sources of [[calcium]] and [[potassium]] and many countries mandate that milk be fortified with [[vitamin A]] and [[vitamin D]]. Consequently, in dairy consuming societies, dairy is often a main source of these nutrients; and, for [[lacto-vegetarian]]s, a main source of [[vitamin B12]]. Individuals who reduce or eliminate consumption of dairy must obtain these nutrients elsewhere. Asian populations for whom dairy is not part of their food culture do not present decreased health and sometimes present above average health, like [[Japan]]. Plant based milk substitutes are not naturally rich in calcium, potassium, or vitamins A or D (and, like all non-animal products, contain no vitamin B12). However, prominent brands are often voluntarily fortified with many of these nutrients, although one should read the label to be certain. An increasing number of calcium-fortified breakfast foods, such as [[orange juice]], [[bread]], and dry [[breakfast cereal|cereal]], have been appearing on supermarket shelves. Many fruits and vegetables are rich in potassium and vitamin A; animal products like meat and eggs are rich in vitamin B12, and the human body itself produces some vitamin D from exposure to direct sunlight. Finally, a [[dietitian]] or physician may recommend a vitamin or mineral supplement to make up for any remaining nutritional shortfall. Lactose-reduced dairy products have the same nutritional content as their full-lactose counterparts, but their taste and appearance may differ slightly. Most [[infants]] with [[gastroenteritis]] due to [[rotavirus]] do not develop lactose intolerance,<ref>{{cite journal |author=Turck D |title=[Prevention and treatment of acute diarrhea in infants] |language=French |journal=Arch Pediatr |volume=14 |issue=11 |pages=1375–8 |year=2007 |pmid=17629685 |doi=10.1016/j.arcped.2007.06.009}}</ref> so these infants do not benefit from being put on a lactose-free diet unless symptoms of lactose intolerance are severe and persistent. === Congenital lactase deficiency === [[Congenital lactase deficiency]], or CLD, is an [[autosomal]] [[recessive]] disorder which prevents the expression of lactase.<ref>{{Emedicine|PED|1270|Lactose Intolerance}} Guandalini S, Frye R, Rivera-Hernández D, Miller L, Borowitz S</ref> Before the 20th century, infants with this disease rarely survived. As substitute and lactose-free infant formulas later became available, nursing infants affected with CLD could now have their normal nutritional needs met. Beyond infancy, individuals with CLD usually have the same nutritional concerns as those affected by secondary lactose intolerance. == See also == * [[Gastroenterology]] * [[Gluten intolerance]] * [[Milk allergy]] * [[Plant milk]] * [[Soy cheese]] * [[Sucrose intolerance]] ==References== {{refbegin}} * {{cite book |title=Paediat. IV. Carbohydrate Metabolism in Children |editor=Ed. E. Rossi, E. Gautier, and J. W. Weber |chapter=Lactosurie et saccharosurie |author=Durand, P. |publisher=Basel |year=1959 |pages=pp. 496–502}} * {{cite journal |author=Holzel A, Schwarz V, Sutcliffe KW |title=Defective lactose absorption causing malnutrition in infancy |journal=Lancet |volume=1 |issue=7083 |pages=1126–8 |year=1959 |pmid=13665980 |doi=}} * {{cite journal |author=Carroccio A, Montalto G, Cavera G, Notarbatolo A |title=Lactose intolerance and self-reported milk intolerance: relationship with lactose maldigestion and nutrient intake. Lactase Deficiency Study Group |journal=J Am Coll Nutr |volume=17 |issue=6 |pages=631–6 |year=1998 |pmid=9853544 |doi= |url=http://www.jacn.org/cgi/content/full/17/6/631}} * {{cite book |author=McGee, Harold |title=On food and cooking: the science and lore of the kitchen |publisher=Scribner |location=New York |year=2004 |pages=pp 14&ndash;15 |chapter=Milk after infancy: dealing with lactose |isbn=0-684-80001-2 |oclc= |doi=}} * {{cite journal |author=Rusynyk RA, Still CD |title=Lactose intolerance |journal=J Am Osteopath Assoc |volume=101 |issue=4 Suppl Pt 1 |pages=S10–2 |year=2001 |pmid=11392211 |doi= |url=http://www.jaoa.org/cgi/reprint/101/4_suppl_1/10S | format=PDF}} {{refend}} ==Footnotes== {{reflist|2}} ==External links== *[http://www.Lactagen.com/ Lactagen- New Product to help reduce lactose intolerant symptoms] *[http://www.lactoseintolerant.org/ Lactose Intolerant Informational Website] *[http://www.nahrungsmittel-intoleranz.com/Laktose/ Great german website about lactose intolerance] *[http://digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance/ United States National Institutes of Health page regarding lactose intolerance] *[http://www.sciam.com/article.cfm?articleID=727EA883-E7F2-99DF-36D89AB12E930315&ref=sciam Scientific American: African Adaptation to Digesting Milk Is "Strongest Signal of Selection Ever"] (East African cattle herding communities rapidly and independently evolved ability to digest lactose) {{Gastroenterology}} {{Carbohydrate metabolic pathology}} [[Category:Metabolic disorders]] [[Category:Milk]] [[Category:Conditions diagnosed by stool test]] [[bg:Лактозна толерантност]] [[de:Laktoseintoleranz]] [[eo:Netolereco de laktozo]] [[es:Intolerancia a la lactosa]] [[fi:Laktoosi-intoleranssi]] [[fr:Intolérance au lactose]] [[he:רגישות ללקטוז]] [[id:Intoleransi laktosa]] [[is:Mjólkuróþol]] [[ja:乳糖不耐症]] [[hu:Laktózérzékenység]] [[nl:Lactose-intolerantie]] [[no:Laktoseintoleranse]] [[pl:Nietolerancja laktozy]] [[pt:Intolerância à lactose]] [[ru:Непереносимость лактозы]] [[sv:Laktosintolerans]] [[uk:Непереносимість лактози]] [[zh:乳糖不耐症]]