Editing Vitamin C (section)

==Deficiency==
Plasma vitamin C is the most widely applied test for vitamin C status.<ref name=PKIN2020VitC>{{cite book |title = Present Knowledge in Nutrition, Eleventh Edition |chapter = Vitamin C | veditors = Marriott MP, Birt DF, Stallings VA, Yates AA |publisher = Academic Press (Elsevier) |year=2020 |location = London, United Kingdom |pages = 155–70 |isbn=978-0-323-66162-1}}</ref> Adequate levels are defined as near 50 μmol/L. [[Hypovitaminosis]] of vitamin C is defined as less than 23 μmol/L, and [[Vitamin deficiency|deficiency]] as less than 11.4 μmol/L.<ref name=Schleicher2009>{{cite journal |vauthors=Schleicher RL, Carroll MD, Ford ES, Lacher DA |title=Serum vitamin C and the prevalence of vitamin C deficiency in the United States: 2003-2004 National Health and Nutrition Examination Survey (NHANES) |journal=The American Journal of Clinical Nutrition |volume=90 |issue=5 |pages=1252–63 |date=November 2009 |pmid=19675106 |doi=10.3945/ajcn.2008.27016 | doi-access = free | title-link = doi | issn = 0002-9165}}</ref> For people 20 years of age or above, data from the US 2017–18 [[National Health and Nutrition Examination Survey]] showed mean serum concentrations of 53.4 {{nbsp}}μmol/L. The percent of people reported as deficient was 5.9%.<ref name="Narayanan-2021">{{cite journal |vauthors=Narayanan S, Kumar SS, Manguvo A, Friedman E |title=Current estimates of serum vitamin C and vitamin C deficiency in the United States |journal=Curr Dev Nutr |volume=7 |issue=5 |pages=1067 |date=June 2021 |doi=10.1093/cdn/nzab053_060|pmc=8180804 }}</ref> Globally, vitamin C deficiency is common in low and middle-income countries, and not uncommon in high income countries. In the latter, prevalence is higher in males than in females.<ref name=Rowe2020>{{cite journal |vauthors=Rowe S, Carr AC |title=Global vitamin C status and prevalence of deficiency: A cause for concern? |journal=Nutrients |volume=12 |issue=7 |date=July 2020 |page=2008 |pmid=32640674 |pmc=7400810 |doi=10.3390/nu12072008 |doi-access=free |url=}}</ref>

Plasma levels are considered saturated at about 65 μmol/L, achieved by intakes of 100 to 200&nbsp;mg/day, which are well above the recommended intakes. Even higher oral intake does not further raise plasma nor tissue concentrations because absorption efficiency decreases and any excess that is absorbed is excreted in urine.<ref name=PKIN2020VitC/>

=== Diagnostic testing ===
Vitamin C content in plasma is used to determine vitamin status. For research purposes, concentrations can be assessed in [[leukocyte]]s and tissues, which are normally maintained at an order of magnitude higher than in plasma via an energy-dependent transport system, depleted slower than plasma concentrations during dietary deficiency and restored faster during dietary repletion,<ref name="DRItext" />{{rp|pages=103–109}} but these analysis are difficult to measure, and hence not part of standard diagnostic testing.<ref name=PKIN2020VitC/><ref name="pmid15820776">{{cite journal | vauthors = Emadi-Konjin P, Verjee Z, Levin AV, Adeli K | title = Measurement of intracellular vitamin C levels in human lymphocytes by reverse phase high performance liquid chromatography (HPLC) | journal = Clinical Biochemistry | volume = 38 | issue = 5 | pages = 450–6 | date = May 2005 | pmid = 15820776 | doi = 10.1016/j.clinbiochem.2005.01.018 }}</ref>