<tablep> <tbody> <tr> <th colspan="2"strong>&nbsp;Lactose intolerance</th> </tr> <tr> <th scope="row">Synonyms</th> <td>Lactase deficiency, hypolactasia</td> </tr> <tr> <td colspan="2"strong>&nbsp;is a condition in which people have symptoms due to the decreased ability to digest&nbsp;<a href="https://en.wikipedia.org/wiki/File:Lactose_Haworth.svgLactose"><img alttitle="Lactose Haworth.svg" src="https://upload.wikimedia.org/wikipedia/commons/thumb/3/36/Lactose_Haworth.svg/300px-Lactose_Haworth.svg.png" style="height:265px; width:300px" />lactose</a></td> </tr> <tr> <td colspan="2">Lactose is made up of, a sugar found in&nbsp;<a href="https://en.wikipedia.org/wiki/DisaccharideDairy_product" title="DisaccharideDairy product">two simple sugarsdairy products</a>.</td> </tr> <tr> <th scopespan style="row"><a href="httpsfont-size://en.wikipedia10.org/wiki/Specialty_(medicine)" title="Specialty (medicine)8333px">Specialty</a></th> <tdspan>Those affected vary in the amount of lactose they can tolerate before symptoms develop.&nbsp;Symptoms may include&nbsp;<a href="https://en.wikipedia.org/wiki/GastroenterologyAbdominal_pain" title="GastroenterologyAbdominal pain">Gastroenterologyabdominal pain</a></td> </tr> <tr> <th scope="row">Symptoms</th> <td>Abdominal pain,&nbsp;<a href="https://en.wikipedia.org/wiki/Bloating" title="Bloating">bloating</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Diarrhea" title="Diarrhea">diarrhea</a>, gas,&nbsp;<a href="https://en.wikipedia.org/wiki/NauseaFlatulence" title="NauseaFlatulence">nauseagas</a>^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}</td> </tr> <tr> <th scope="row"><a href="https://en.wikipedia.org/wiki/Complication_(medicine)" title="Complication (medicine)">Complications</a></th> <td>Does not cause damage to the GI tract^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Heyman2006-2">[2]</a>}</td> </tr> <tr> <th scope="row">Usual onset</th> <td>30&ndash;120 min after dairy products^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}</td> </tr> <tr> <th scope="row">Causes</th> <td>Decreased ability to digest, and&nbsp;<a href="https://en.wikipedia.org/wiki/LactoseNausea" title="LactoseNausea">lactose</a>(genetic, small intestine injury)^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}</td> </tr> <tr> <th scope="row"><a href="https://en.wikipedia.org/wiki/Diagnostic_method" title="Diagnostic method">Diagnostic method</a></th> <td>Symptoms resolve following eliminating lactose^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}</td> </tr> <tr> <th scope="row"><a href="https://en.wikipedia.org/wiki/Differential_diagnosis" title="Differential diagnosis">Differential diagnosisnausea</a></th> <td><a href="https://en.wikipedia.org/wiki/Irritable_bowel_syndrome" title="Irritable bowel syndrome">Irritable bowel syndrome</a>,&nbsp;<a href="https://enThese symptoms typically start 30 minutes to two hours after eating or drinking milk-based food.wikipedia.org/wiki/Celiac_disease" title="Celiac disease">celiac disease</a>,&nbsp;<Severity typically depends on the amount a href="https://enperson eats or drinks.wikipedia.org/wiki/Inflammatory_bowel_disease" title="Inflammatory bowel disease">inflammatory bowel disease</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Milk_allergy" title="Milk allergy">milk allergy</a>^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}</td> </tr> <tr> <th scope="row">Treatment</th> <td>Decreasing lactose in Lactose intolerance does not cause damage to the diet,&nbsp;<a href="https://en.wikipedia.org/wiki/Lactase_supplementsGastrointestinal_tract" title="Lactase supplementsGastrointestinal tract">lactase supplementsgastrointestinal tract</a>, treat the underlying cause^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}</td> </tr> <tr> <th scope="row">Frequency</th> <td>10% (Northern Europe) to 95% (parts of Asia and Africa)^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Deng2015-3">[3]</a>}</td> </tr> </tbody></tablep>

<p><strong>Lactose intolerance</strong>&nbsp;is a condition in which people have symptoms due to the decreased ability to digestlack of&nbsp;<a href="https://en.wikipedia.org/wiki/LactoseEnzyme" title="LactoseEnzyme">lactoseenzyme</a>, a sugar found in&nbsp;<a href="https://en.wikipedia.org/wiki/Dairy_productLactase" title="Dairy productLactase">dairy productslactase</a>.^{&nbsp;in the&nbsp;<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1Small_intestines">[1]</a>}Those affected vary in the amount of lactose they can tolerate before symptoms develop.^{<a hreftitle="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1Small intestines">[1]small intestines</a>}&nbsp;Symptoms may includeto break lactose down into&nbsp;<a href="https://en.wikipedia.org/wiki/Abdominal_painGlucose" title="Abdominal painGlucose">abdominal painglucose</a>,&nbsp;and&nbsp;<a href="https://en.wikipedia.org/wiki/BloatingGalactose" title="BloatingGalactose">bloatinggalactose</a>.&nbsp;There are four types: primary,secondary, developmental, and congenital.&nbsp;Primary lactose intolerance occurs as the number of lactase declines as people age.<a hrefspan style="httpsfont-size://en.wikipedia10.org/wiki/Diarrhea" title="Diarrhea8333px">diarrhea</aspan>Secondary lactose intolerance is due to injury to the small intestine such as from infection,&nbsp;<a href="https://en.wikipedia.org/wiki/FlatulenceCeliac_disease" title="FlatulenceCeliac disease">gasceliac disease</a>, and&nbsp;<a href="https://en.wikipedia.org/wiki/NauseaInflammatory_bowel_disease" title="NauseaInflammatory bowel disease">nauseainflammatory bowel disease</a>, or other diseases.<sup><a hrefspan style="httpsfont-size://en10.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-18333px">[1]</a></supspan>Developmental lactose intolerance may occur in&nbsp;These symptoms typically start 30 minutes to two hours after eating or drinking milk-based food.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1Premature_babies" title="Premature babies">[1]premature babies</a>}&nbsp;Severity typically depends on the amount and usually improves over a person eats or drinks.^{<a href="https://en.wikipediashort period of time.org/wiki/Lactose_intolerance#cite_note-NIH2014Dig-1">[1]</a>}&nbsp;Lactose Congenital lactose intolerance does not cause damage to theis an extremely rare&nbsp;<a href="https://en.wikipedia.org/wiki/Gastrointestinal_tractGenetic_disorder" title="Gastrointestinal tractGenetic disorder">gastrointestinal tractgenetic disorder</a>&nbsp;in which little or no lactase is made from birth.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Heyman2006-2">[2]</a>}</p>

<p>&nbsp;</p> <p><span style="font-size:20px">Causes</span></p> <hr /><p>Lactose intolerance is due to a consequence of&nbsp;<a href="https://en.wikipedia.org/wiki/Lactase" title="Lactase">lactase</a>&nbsp;deficiency, which may be genetic (<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#Primary_hypolactasia">primary hypolactasia</a>&nbsp;and&nbsp;<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#Primary_congenital_alactasia">primary congenital alactasia</a>) or environmentally induced (<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#Secondary_hypolactasia_or_acquired_hypoalactasia">secondary or acquired hypoalactasia</a>). In either case, symptoms are caused by insufficient levels of lactase in the lack lining ofthe&nbsp;<a href="https://en.wikipedia.org/wiki/EnzymeDuodenum" title="EnzymeDuodenum">enzymeduodenum</a>. Lactose, a&nbsp;<a href="https://en.wikipedia.org/wiki/LactaseDisaccharide" title="LactaseDisaccharide">disaccharide</a>&nbsp;molecule found in milk and dairy products, cannot be directly absorbed through the wall of the small intestine into the bloodstream, so, in the absence of lactase, passes intact into the&nbsp;<a href="https://en.wikipedia.org/wiki/Colon_(anatomy)" title="Colon (anatomy)">colon</a>.&nbsp;<a href="https://en.wikipedia.org/wiki/Gut_flora" title="Gut flora">Bacteria</a>&nbsp;in thecolon can metabolise lactose, and the resulting&nbsp;<a href="https://en.wikipedia.org/wiki/Small_intestinesFermentation_(biochemistry)" title="Small intestines">small intestinesfermentation</a>&nbsp;produces copious amounts of gas (a mixture of&nbsp;<a href="https://en.wikipedia.org/wiki/Hydrogen" title="Hydrogen">hydrogen</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Carbon_dioxide" title="Carbon dioxide">carbon dioxide</a>, and&nbsp;<a href="https://en.wikipedia.org/wiki/Methane" title="Methane">methane</a>) that causes the various abdominal symptoms. The unabsorbed sugars and fermentation products also raise the&nbsp;<a href="https://en.wikipedia.org/wiki/Osmotic_pressure" title="Osmotic pressure">osmotic pressure</a>&nbsp;of the colon, causing an increased flow of water into the bowels (diarrhea).</p> <p>The&nbsp;<em>LCT</em>&nbsp;gene provides the instructions for making lactase. The specific DNA sequence in the&nbsp;<em>MCM6</em>&nbsp;gene helps control whether the&nbsp;<em>LCT</em>&nbsp;gene is turned on or off.&nbsp;At least several thousand years ago, some humans developed amutation in the&nbsp;<em>MCM6</em>&nbsp;gene that keeps the&nbsp;<em>LCT</em>&nbsp;gene turned on even after breastfeeding is stopped.&nbsp;Populations that are lactose intolerant lack this mutation. The&nbsp;LCT and&nbsp;<em>MCM6</em>&nbsp;genes are both located on the long arm (q) of chromosome 2 in region 21. The locus can be expressed as 2q21.<span style="font-size:10.8333px"> </span>The lactase deficiency also could be linked to break certain heritage. It is more common in Asian Americans, African Americans, Mexican Americans, and Native Americans.&nbsp;Analysis of the DNA of 94 ancient skeletons in Europe and Russia concluded that the mutation for lactose down tolerance appeared about 4,300 years ago and spread throughout the European population.</p> <p>Some human populations have developed&nbsp;<a href="https://en.wikipedia.org/wiki/Lactase_persistence" title="Lactase persistence">lactase persistence</a>, in which lactase production continues intoadulthood probably as a response to the benefits of being able to digest milk from farm animals.&nbsp;Some have argued that this links intolerance to&nbsp;<a href="https://en.wikipedia.org/wiki/GlucoseNatural_selection" title="GlucoseNatural selection">glucosenatural selection</a>&nbsp;favoring lactase-persistent individuals, but it is also consistent with a physiological response to decrease lactase production when it is not needed in cultures in which dairy products are not an available food source.&nbsp;Although populations in Europe, India, Arabia, andAfrica were first thought to have high rates of lactase persistence because of a single mutation, lactase persistence has been traced to a number of mutations that occurred independently.&nbsp;Different alleles for lactase persistence have developed at least three times in East African populations, with persistence extending from 26% in&nbsp;<a href="https://en.wikipedia.org/wiki/Tanzania" title="Tanzania">Tanzania</a>&nbsp;to 88% in the&nbsp;<a href="https://en.wikipedia.org/wiki/Beja_people" title="Beja people">Beja</a>&nbsp;pastoralist population in&nbsp;<a href="https://en.wikipedia.org/wiki/GalactoseSudan" title="GalactoseSudan">galactoseSudan</a>.</p> <p>The accumulation of&nbsp;<a href="https://en.wikipedia.org/wiki/Epigenetics" title="Epigenetics">Epigenetic</a>&nbsp;factors, primarily&nbsp;<a href="https://en.wikipedia.org/wiki/DNA_methylation" title="DNA methylation">DNA methylation</a>, in the&nbsp;<em>LCT</em>&nbsp;and&nbsp;<em>MCM6</em>&nbsp;gene may also contribute to the onset of lactose intolerance in adults.</p> <p>Lactose intolerance is classified according to its causes as:</p> <h3>Primary hypolactasia[<a href="https://en.wikipedia.org/w/index.php?title=Lactose_intolerance&amp;action=edit&amp;section=4" title="Edit section: Primary hypolactasia">edit</a>]</h3> <p>Primary hypolactasia, or primary lactase deficiency, is genetic, only affects adults, and is caused by the absence of a lactase persistence allele. In individuals without the lactase persistence allele, less lactase is produced by the body over time, leading to hypolactasia in adulthood.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Heyman2006-2">[2]</a>}^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Deng2015variant-325">[325]</a>}&nbsp;There are four types: primaryThe frequency of lactase persistence, which allows lactose tolerance, secondaryvaries enormously worldwide, developmentalwith the highest prevalence in Northwestern Europe, declines across southern Europe and the Middle East and congenitalis low in Asia and most of Africa, although it is common in pastoralist populations from Africa.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014DigDeng2015-13">[13]</a>}&nbsp;Primary lactose intolerance occurs as the amount of lactase declines as people age.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014DigSwallow_2003-126">[126]</a>}</p> <h3>Secondary lactose intolerance hypolactasia[<a href="https://en.wikipedia.org/w/index.php?title=Lactose_intolerance&amp;action=edit&amp;section=5" title="Edit section: Secondary hypolactasia">edit</a>]</h3> <p>Secondary hypolactasia or secondary lactase deficiency, also called acquired hypolactasia or acquired lactase deficiency, is due to caused by an injury to the &nbsp;<a href="https://en.wikipedia.org/wiki/Small_intestine" title="Small intestine">small intestine such as from infection</a>. This form of lactose intolerance can occur in both infants and lactase persistent adults and is generally reversible.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-27">[27]</a>}&nbsp;It may be caused by acute&nbsp;<a href="https://en.wikipedia.org/wiki/Gastroenteritis" title="Gastroenteritis">gastroenteritis</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Celiac_diseaseCoeliac_disease" title="Celiac Coeliac disease">celiac coeliac disease</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Inflammatory_bowel_diseaseCrohn%27s_disease" title="Inflammatory bowel Crohn's disease">inflammatory bowel Crohn&#39;s disease</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Ulcerative_colitis" title="Ulcerative colitis">ulcerative colitis</a>,^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-28">[28]</a>}&nbsp;<a href="https://en.wikipedia.org/wiki/Chemotherapy" title="Chemotherapy">chemotherapy</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Intestinal_parasites" title="Intestinal parasites">intestinal parasites</a>&nbsp;(such as&nbsp;<a href="https://en.wikipedia.org/wiki/Giardia" title="Giardia">giardia</a>), or other diseasesenvironmental causes.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014DigHeyman2006-12">[12]</a>}^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-BerniCananiPezzella2016SwagertyWalling2002-29">[29]</a>}^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-430">[30]</a>}^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-eMedicine_pediatric-31">[31]</a>}^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-SwagertyWalling2002-29">[429]</a>}</p> <h3>Primary congenital alactasia[<a href="https://en.wikipedia.org/w/index.php?title=Lactose_intolerance&nbspamp;action=edit&amp;Developmental lactose intolerance may occur insection=6" title="Edit section: Primary congenital alactasia">edit</a>]</h3> <p>Primary congenital alactasia, also called congenital lactase deficiency, is an extremely rare,&nbsp;<a href="https://en.wikipedia.org/wiki/Premature_babiesAutosomal_recessive" title="Premature babiesAutosomal recessive">premature babiesautosomal recessive</a>&nbsp;and usually improves over enzyme defect that prevents lactase expression from birth.^{<a short period of timehref="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Heyman2006-2">[2]</a>}^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-NIH2014DigDeng2015-13">[13]</a>}&nbsp;Congenital People with congenital lactase deficiency cannot digest lactose intolerance from birth, so cannot digest breast milk. This genetic defect is an extremely rarecharacterized by a complete lack of lactase (alactasia). About 40 cases have been reported worldwide, mainly limited to&nbsp;<a href="https://en.wikipedia.org/wiki/Genetic_disorderFinland" title="Genetic disorderFinland">genetic disorderFinland</a>.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Deng2015-3">[3]</a>}&nbsp;in which little or no Before the 20th century, babies born with congenital lactase is made from birthdeficiency often did not survive,^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-Heyman2006-2">[2]</a>}&nbsp;but death rates decreased with&nbsp;<a href="https://en.wikipedia.org/wiki/Soybean" title="Soybean">soybean</a>-derived&nbsp;<a href="https://en.wikipedia.org/wiki/Infant_formula" title="Infant formula">infant formulas</a>and manufactured lactose-free dairy products.^{<a href="https://en.wikipedia.org/wiki/Lactose_intolerance#cite_note-32">[32]</a>}</p>