Editing Vitamin A (section)

===Primary causes===
Vitamin A deficiency is common in [[Developing country|developing countries]], especially in [[Sub-Saharan Africa]] and [[Southeast Asia]]. Deficiency can occur at any age, but is most common in pre-school-age children and pregnant women, the latter due to a need to transfer retinol to the fetus. The causes are low intake of retinol-containing, animal-sourced foods and low intake of carotene-containing, plant-sourced foods. Vitamin A deficiency is estimated to affect approximately one third of children under the age of five around the world,<ref>{{cite web |publisher=[[World Health Organization]] |title=Global prevalence of vitamin A deficiency in populations at risk 1995–2005 |url=http://apps.who.int/iris/bitstream/10665/44110/1/9789241598019_eng.pdf |work=WHO global database on vitamin A deficiency |year=2009 |access-date=28 June 2017 |archive-date=15 December 2017 |archive-url=https://web.archive.org/web/20171215143955/http://apps.who.int/iris/bitstream/10665/44110/1/9789241598019_eng.pdf |url-status=live }}</ref> possibly leading to the deaths of 670,000 children under five annually.<ref>{{cite journal | vauthors = Black RE, Allen LH, Bhutta ZA, Caulfield LE, de Onis M, Ezzati M, Mathers C, Rivera J | title = Maternal and child undernutrition: global and regional exposures and health consequences | journal = Lancet | volume = 371 | issue = 9608 | pages = 243–260 | date = January 2008 | pmid = 18207566 | doi = 10.1016/S0140-6736(07)61690-0 | url = https://naldc-legacy.nal.usda.gov/naldc/download.xhtml?id=10965&content=PDF | url-status = dead | s2cid = 3910132 | collaboration = Maternal and Child Undernutrition Study Group | archive-url = https://web.archive.org/web/20211016033636/https://naldc-legacy.nal.usda.gov/naldc/download.xhtml?id=10965&content=PDF | archive-date = 16 October 2021 }}</ref>

Between 250,000 and 500,000 children in developing countries become blind each year owing to vitamin A deficiency.<ref name="ods"/> Vitamin A deficiency is "the leading cause of preventable childhood blindness", according to [[UNICEF]].<ref name=UNICEFvitaminA>{{cite web | url = http://www.unicef.org/specialsession/about/sgreport-pdf/12_VitaminADeficiency_D7341Insert_English.pdf | title = Vitamin A Deficiency | work = UNICEF | access-date = 3 June 2015 | archive-date = 12 September 2016 | archive-url = https://web.archive.org/web/20160912193103/http://www.unicef.org/specialsession/about/sgreport-pdf/12_VitaminADeficiency_D7341Insert_English.pdf | url-status = dead }}</ref><ref name="Akhtar2013"/> It also increases the risk of death from common childhood conditions, such as [[diarrhea]]. UNICEF regards addressing vitamin A deficiency as critical to reducing [[child mortality]], the fourth of the [[United Nations]]' [[Millennium Development Goals]].<ref name=UNICEFvitaminA/>

During diagnosis, night blindness and [[xerophthalmia|dry eyes]] are signs of vitamin A deficiency that can be recognized without requiring biochemical tests. Plasma retinol is used to confirm vitamin A status. A plasma concentration of about 2.0 μmol/L is normal; less than 0.70 μmol/L (equivalent to 20 μg/dL) indicates moderate vitamin A deficiency, and less than 0.35 μmol/L (10 μg/dL) indicates severe vitamin A deficiency. Breast milk retinol of less than 8 μg/gram [[milk fat]] is considered insufficient.<ref name=PKIN2020VitA/> One weakness of these measures is that they are not good indicators of liver vitamin A stores as retinyl esters in [[hepatic stellate cell]]s. The amount of vitamin A leaving the liver, bound to retinol binding protein (RBP), is under tight control as long as there are sufficient liver reserves. Only when liver content of vitamin A drops below approximately 20 μg/gram will concentration in the blood decline.<ref name="DRI VitA"/><ref name=Tanumihardjo>{{cite journal | vauthors = Tanumihardjo SA | title = Vitamin A: biomarkers of nutrition for development | journal = The American Journal of Clinical Nutrition | volume = 94 | issue = 2 | pages = 658S–665S | date = August 2011 | pmid = 21715511 | pmc = 3142734 | doi = 10.3945/ajcn.110.005777 }}</ref>