Editing Vitamin C (section)

==Health effects==
[[File:VitaminSupplementPills2.jpg|thumb|alt=Rows and rows of dietary supplement bottles on shelves |Vitamin C supplements among other dietary supplements at a US drug store]]
Vitamin C has a definitive role in treating scurvy, which is a disease caused by vitamin{{nbsp}}C deficiency. Beyond that, a role for vitamin{{nbsp}}C as prevention or treatment for various diseases is disputed, with reviews often reporting conflicting results. No effect of vitamin{{nbsp}}C supplementation reported for overall mortality.<ref name="pmid22419320">{{cite journal | vauthors = Bjelakovic G, Nikolova D, Gluud LL, Simonetti RG, Gluud C | title = Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases | journal = The Cochrane Database of Systematic Reviews | volume = 2012 | issue = 3 | pages = CD007176 | date = March 2012 | pmid = 22419320 | doi = 10.1002/14651858.CD007176.pub2 | pmc = 8407395 | hdl = 10138/136201 | hdl-access = free }}</ref> It is on the [[WHO Model List of Essential Medicines|World Health Organization's List of Essential Medicines]]<ref name="WHO23rd">{{cite book | vauthors = ((World Health Organization)) | title = The selection and use of essential medicines 2023: web annex A: World Health Organization model list of essential medicines: 23rd list (2023) | year = 2023 | hdl = 10665/371090 | author-link = World Health Organization | publisher = World Health Organization | location = Geneva | id = WHO/MHP/HPS/EML/2023.02 | hdl-access=free }}</ref> and on the World Health Organization's Model Forumulary.<ref name = "WHO Formulary 2008">{{cite book | title = WHO Model Formulary 2008 | year = 2009 | isbn = 978-92-4-154765-9 | vauthors = ((World Health Organization)) | veditors = Stuart MC, Kouimtzi M, Hill SR | hdl = 10665/44053 | author-link = World Health Organization | publisher = World Health Organization | hdl-access=free }}</ref> In 2022, it was the 226th most commonly prescribed medication in the United States, with more than 1{{nbsp}}million prescriptions.<ref>{{cite web | title=The Top 300 of 2022 | url=https://clincalc.com/DrugStats/Top300Drugs.aspx | website=ClinCalc | access-date=30 August 2024 | archive-date=30 August 2024 | archive-url=https://web.archive.org/web/20240830202410/https://clincalc.com/DrugStats/Top300Drugs.aspx | url-status=live }}</ref><ref>{{cite web | title = Ascorbic Acid Drug Usage Statistics, United States, 2013 - 2022 | website = ClinCalc | url = https://clincalc.com/DrugStats/Drugs/AscorbicAcid | access-date = 30 August 2024 }}</ref>

===Scurvy===
{{Main|Scurvy}}

[[Scurvy]] is a disease resulting from a deficiency of vitamin C. Without this vitamin, [[collagen]] made by the body is too unstable to perform its function and several other [[enzyme]]s in the body do not operate correctly. Early symptoms are malaise and lethargy, progressing to shortness of breath, bone pain and susceptibility to bruising. As the disease progressed, it is characterized by [[Hyperkeratosis|spots]] on and [[Ecchymosis|bleeding]] under the skin and bleeding gums. The skin lesions are most abundant on the thighs and legs. A person with the ailment looks pale, feels depressed, and is partially immobilized. In advanced scurvy there is fever, old wounds may become open and  [[suppuration|suppurating]], loss of [[Tooth|teeth]], convulsions and, eventually, death. Until quite late in the disease the damage is reversible, as healthy collagen replaces the defective collagen with vitamin{{nbsp}}C repletion.<ref name=lpi2018 /><ref name=AHFS2016 /><ref name="pmid21402244">{{cite journal | vauthors = Magiorkinis E, Beloukas A, Diamantis A | title = Scurvy: past, present and future. | journal = The European Journal of Internal Medicine | volume = 22 | issue = 2 | pages = 147–52 | date = April 2011 | pmid = 21402244 | doi = 10.1016/j.ejim.2010.10.006}}</ref>

Notable human dietary studies of experimentally induced scurvy were conducted on [[conscientious objector]]s during World War II in Britain and on Iowa state prisoners in the late 1960s to the 1980s. Men in the prison study developed the first signs of scurvy about four weeks after starting the vitamin C-free diet, whereas in the earlier British study, six to eight months were required, possibly due to the pre-loading of this group with a 70&nbsp;mg/day supplement for six weeks before the scorbutic diet was fed. Men in both studies had blood levels of ascorbic acid too low to be accurately measured by the time they developed signs of scurvy. These studies both reported that all obvious symptoms of scurvy could be completely reversed by supplementation of only 10&nbsp;mg a day.<ref name="pmid4977512">{{cite journal | vauthors = Hodges RE, Baker EM, Hood J, Sauberlich HE, March SC | title = Experimental scurvy in man | journal = The American Journal of Clinical Nutrition | volume = 22 | issue = 5 | pages = 535–48 | date = May 1969 | pmid = 4977512 | doi = 10.1093/ajcn/22.5.535}}</ref><ref name="pmid16510534">{{cite journal | vauthors = Pemberton J | title = Medical experiments carried out in Sheffield on conscientious objectors to military service during the 1939-45 war | journal = International Journal of Epidemiology | volume = 35 | issue = 3 | pages = 556–8 | date = June 2006 | pmid = 16510534 | doi = 10.1093/ije/dyl020 | doi-access = free | title-link = doi }}</ref> Treatment of scurvy can be with vitamin{{nbsp}}C-containing foods or dietary supplements or injection.<ref name=AHFS2016/><ref name="DRItext" />{{rp|page=101}}

===Sepsis===
People in [[sepsis]] may have micronutrient deficiencies, including low levels of vitamin C.<ref name="pmid29984680">{{cite journal | vauthors = Belsky JB, Wira CR, Jacob V, Sather JE, Lee PJ | title = A review of micronutrients in sepsis: the role of thiamine, L-carnitine, vitamin C, selenium and vitamin D | journal = Nutrition Research Reviews | volume = 31 | issue = 2 | pages = 281–90 | date = December 2018 | pmid = 29984680 | doi = 10.1017/S0954422418000124 | s2cid = 51599526 }}</ref> An intravenous intake of doses much higher than the RDA, such as {{val|3|u=g/day}} or more, appears to be needed to maintain normal plasma concentrations in people with sepsis, as the body's demand for vitamin C may increase significantly due to the heightened inflammatory response and oxidative stress.<ref name="pmid30452091">{{cite journal |vauthors=Langlois PL, Manzanares W, Adhikari NK, Lamontagne F, Stoppe C, Hill A, Heyland DK |title=Vitamin C Administration to the Critically Ill: A Systematic Review and Meta-Analysis |journal=JPEN J Parenter Enteral Nutr |volume=43 |issue=3 |pages=335–346 |date=March 2019 |pmid=30452091 |doi=10.1002/jpen.1471 |url=}}</ref><ref name=Liang2023/><ref name="pmid25635594">{{cite journal |vauthors=Berger MM, Oudemans-van Straaten HM |title=Vitamin C supplementation in the critically ill patient |journal=Curr Opin Clin Nutr Metab Care |volume=18 |issue=2 |pages=193–201 |date=March 2015 |pmid=25635594 |doi=10.1097/MCO.0000000000000148 |s2cid=37895257 |url=}}</ref> Sepsis mortality may be reduced with administration of intravenous vitamin C.<ref name="pmid37111066">{{cite journal |vauthors=Xu C, Yi T, Tan S, Xu H, Hu Y, Ma J, Xu J |title=Association of oral or intravenous vitamin C supplementation with mortality: A systematic review and meta-analysis |journal=Nutrients |volume=15 |issue=8 |date=April 2023 |page=1848 |pmid=37111066 |pmc=10146309 |doi=10.3390/nu15081848 |doi-access=free |url=}}</ref><ref name="pmid37599680">{{cite journal |vauthors=Liang H, Mu Q, Sun W, Liu L, Qiu S, Xu Z, Cui Y, Yan Y, Sun T |title=Effect of intravenous vitamin C on adult septic patients: a systematic review and meta-analysis |journal=Front Nutr |volume=10 |issue= |pages=1211194 |date=2023 |pmid=37599680 |pmc=10437115 |doi=10.3389/fnut.2023.1211194 |doi-access=free |url=}}</ref>

===Common cold===
[[File:Linus Pauling.jpg|alt=1955 black-and-white photo of Nobel Prize winner, Linus Pauling.|thumb|upright|The Nobel Prize winner [[Linus Pauling]] advocated taking vitamin C for the [[common cold]] in [[Vitamin C and the Common Cold (book)|a 1970 book]].]]

Research on vitamin{{nbsp}}C in the common cold has been divided into effects on prevention, duration, and severity. Oral intakes of more than 200&nbsp;mg/day taken on a regular basis was not effective in prevention of the common cold. Restricting analysis to trials that used at least 1000&nbsp;mg/day also saw no prevention benefit. However, taking a vitamin{{nbsp}}C supplement on a regular basis did reduce the average duration of the illness by 8% in adults and 14% in children, and also reduced the severity of colds.<ref name=Hem2013>{{cite journal |vauthors = Hemilä H, Chalker E |title = Vitamin C for preventing and treating the common cold |journal = The Cochrane Database of Systematic Reviews |issue = 1 |pages = CD000980 |date = January 2013 |volume = 2013 |pmid = 23440782 |doi = 10.1002/14651858.CD000980.pub4 |pmc = 1160577}}</ref> Vitamin C taken on a regular basis reduced the duration of severe symptoms but had no effect on the duration of mild symptoms.<ref name=Hem2023>{{cite journal |vauthors=Hemilä H, Chalker E |title=Vitamin C reduces the severity of common colds: a meta-analysis |journal=BMC Public Health |volume=23 |issue=1 |pages=2468 |date=December 2023 |pmid=38082300 |pmc=10712193 |doi=10.1186/s12889-023-17229-8 |url= | doi-access = free | title-link = doi }}</ref> Therapeutic use, meaning that the vitamin was not started unless people started to feel the beginnings of a cold, had no effect on the duration or severity of the illness.<ref name="Hem2013" />

Vitamin C distributes readily in high concentrations into [[immune system|immune cells]], promotes [[natural killer cell]] activities, promotes [[lymphocyte]] proliferation, and is depleted quickly during infections, effects suggesting a prominent role in immune system function.<ref name="Wintergerst-2006">{{cite journal | vauthors = Wintergerst ES, Maggini S, Hornig DH | s2cid = 21756498 | title = Immune-enhancing role of vitamin C and zinc and effect on clinical conditions | journal = Annals of Nutrition & Metabolism | volume = 50 | issue = 2 | pages = 85–94 | year = 2006 | pmid = 16373990 | doi = 10.1159/000090495 | url = http://doc.rero.ch/record/303675/files/S0029665108006927.pdf | access-date = August 25, 2019 | archive-date = July 22, 2018 | archive-url = https://web.archive.org/web/20180722160530/http://doc.rero.ch/record/303675/files/S0029665108006927.pdf | url-status = live }}</ref> The [[European Food Safety Authority]] concluded there is a [[causality|cause and effect relationship]] between the dietary intake of vitamin C and functioning of a normal immune system in adults and in children under three years of age.<ref name="efsa09">{{cite journal |author=EFSA Panel on Dietetic Products, Nutrition and Allergies |title=Scientific Opinion on the substantiation of health claims related to vitamin C and protection of DNA, proteins and lipids from oxidative damage (ID 129, 138, 143, 148), antioxidant function of lutein (ID 146), maintenance of vision (ID 141, 142), collagen formation (ID 130, 131, 136, 137, 149), function of the nervous system (ID 133), function of the immune system (ID 134), function of the immune system during and after extreme physical exercise (ID 144), non-haem iron absorption (ID 132, 147), energy-yielding metabolism (ID 135), and relief in case of irritation in the upper respiratory tract (ID 1714, 1715) pursuant to Article 13(1) of Regulation (EC) No 1924/2006 |journal=EFSA Journal |volume=7 |issue=9 |year=2009 |page=1226 |doi=10.2903/j.efsa.2009.1226| doi-access = free | title-link = doi }}</ref><ref name="efsa15">{{cite journal |author=EFSA Panel on Dietetic Products, Nutrition and Allergies |title=Vitamin C and contribution to the normal function of the immune system: evaluation of a health claim pursuant to Article 14 of Regulation (EC) No 1924/2006 |journal=EFSA Journal |year=2015 |volume=13 |issue=11 |page=4298 |doi=10.2903/j.efsa.2015.4298| doi-access = free | title-link = doi |hdl=11380/1296052 |hdl-access=free }}</ref>

===COVID-19===
{{see also|COVID-19 drug repurposing research#Vitamin C|COVID-19 misinformation#Vitamin C}}

During March through July 2020, vitamin C was the subject of more US FDA warning letters than any other ingredient for claims for prevention and/or treatment of COVID-19.<ref name="pmid33001378">{{cite journal |vauthors=Bramstedt KA |title=Unicorn poo and blessed waters: COVID-19 quackery and FDA Warning Letters |journal=Ther Innov Regul Sci |date=October 2020 |volume=55 |issue=1 |pages=239–44 |pmid=33001378 |pmc=7528445 |doi=10.1007/s43441-020-00224-1 }}</ref> In April 2021, the US [[National Institutes of Health]] (NIH) COVID-19 Treatment Guidelines stated that "there are insufficient data to recommend either for or against the use of vitamin{{nbsp}}C for the prevention or treatment of COVID-19."<ref name="COVID-19 Treatment Guidelines-2021">{{cite web |title=Vitamin C |url=https://www.covid19treatmentguidelines.nih.gov/therapies/supplements/vitamin-c/ |website=COVID-19 Treatment Guidelines |date=April 21, 2021 |access-date=January 2, 2022 |archive-date=November 20, 2021 |archive-url=https://web.archive.org/web/20211120131306/https://www.covid19treatmentguidelines.nih.gov/therapies/supplements/vitamin-c/ |url-status=live }}</ref> In an update posted December 2022, the NIH position was unchanged:
* There is insufficient evidence for the COVID-19 Treatment Guidelines Panel (the Panel) to recommend either for or against the use of vitamin C for the treatment of COVID-19 in nonhospitalized patients.
* There is insufficient evidence for the Panel to recommend either for or against the use of vitamin C for the treatment of COVID-19 in hospitalized patients.<ref name="U.S. National Institutes of Health-2022">{{cite web |url=https://www.covid19treatmentguidelines.nih.gov/therapies/supplements/vitamin-c/ |title=COVID-19 treatment guidelines |date=December 26, 2022 |website=U.S. National Institutes of Health |access-date=December 18, 2023 |archive-date=November 20, 2021 |archive-url=https://web.archive.org/web/20211120131306/https://www.covid19treatmentguidelines.nih.gov/therapies/supplements/vitamin-c/ |url-status=live }}</ref>

For people hospitalized with severe COVID-19 there are reports of a significant reduction in the risk of all-cause, in-hospital mortality with the administration of vitamin C relative to no vitamin C. There were no significant differences in ventilation incidence, hospitalization duration or length of intensive care unit stay between the two groups. The majority of the trials incorporated into these meta-analyses used intravenous administration of the vitamin.<ref name=Kow2023>{{cite journal |vauthors=Kow CS, Hasan SS, Ramachandram DS |title=The effect of vitamin C on the risk of mortality in patients with COVID-19: a systematic review and meta-analysis of randomized controlled trials | journal=Inflammopharmacology |volume=31 |issue=6 |pages=3357–62 |date=December 2023 |pmid= 37071316|pmc=10111321 |doi=10.1007/s10787-023-01200-5 |url=}}</ref><ref name=Huang2022>{{cite journal |vauthors=Huang WY, Hong J, Ahn SI, Han BK, Kim YJ |title=Association of vitamin C treatment with clinical outcomes for COVID-19 patients: A systematic review and meta-analysis |journal=Healthcare |volume=10 |issue=12 |date=December 2022 |page=2456 |pmid=36553979 |pmc=9777834 |doi=10.3390/healthcare10122456 |url= | doi-access = free | title-link = doi }}</ref><ref name=Olczak2022>{{cite journal |vauthors=Olczak-Pruc M, Swieczkowski D, Ladny JR, Pruc M, Juarez-Vela R, Rafique Z, Peacock FW, Szarpak L |title=Vitamin C supplementation for the treatment of COVID-19: A systematic review and meta-analysis |journal=Nutrients |volume=14 |issue=19 |date=October 2022 |page=4217 |pmid=36235869 |pmc=9570769 |doi=10.3390/nu14194217 |url= | doi-access = free | title-link = doi }}</ref> Acute kidney injury was lower in people treated with vitamin C treatment. There were no differences in the frequency of other adverse events due to the vitamin.<ref name=Olczak2022 /> The conclusion was that further large-scale studies are needed to affirm its mortality benefits before issuing updated guidelines and recommendations.<ref name=Kow2023 /><ref name=Huang2022 /><ref name=Olczak2022 />

===Cancer===
Higher vitamin C intake appears to reduce the risk for [[lung cancer]].<ref name="pmid25145261">{{cite journal | vauthors = Luo J, Shen L, Zheng D | title = Association between vitamin C intake and lung cancer: a dose-response meta-analysis | journal = Scientific Reports | volume = 4 | pages = 6161 | date = 2014 | pmid = 25145261 | pmc = 5381428 | doi = 10.1038/srep06161 | bibcode = 2014NatSR...4.6161L }}</ref> There is no evidence that vitamin C supplementation reduces the risk of prostate cancer,<ref name="Stratton J, Godwin M 243–52">{{cite journal | vauthors = Stratton J, Godwin M | title = The effect of supplemental vitamins and minerals on the development of prostate cancer: a systematic review and meta-analysis | journal = Family Practice | volume = 28 | issue = 3 | pages = 243–52 | date = June 2011 | pmid = 21273283 | doi = 10.1093/fampra/cmq115 | doi-access = free | title-link = doi }}</ref> [[colorectal cancer]]<ref name="pmid25335850">{{cite journal |vauthors=Heine-Bröring RC, Winkels RM, Renkema JM, Kragt L, van Orten-Luiten AC, Tigchelaar EF, Chan DS, Norat T, Kampman E |title=Dietary supplement use and colorectal cancer risk: a systematic review and meta-analyses of prospective cohort studies |journal=Int J Cancer |volume=136 |issue=10 |pages=2388–401 |date=May 2015 |pmid=25335850 |doi=10.1002/ijc.29277 |s2cid=44706004 |url=}}</ref> or breast cancer.<ref name="pmid21761132">{{cite journal | vauthors = Fulan H, Changxing J, Baina WY, Wencui Z, Chunqing L, Fan W, Dandan L, Dianjun S, Tong W, Da P, Yashuang Z | title = Retinol, vitamins A, C, and E and breast cancer risk: a meta-analysis and meta-regression | journal = Cancer Causes & Control | volume = 22 | issue = 10 | pages = 1383–96 | date = October 2011 | pmid = 21761132 | doi = 10.1007/s10552-011-9811-y | s2cid = 24867472 }}</ref>

===Cardiovascular disease===
There is no evidence that vitamin C supplementation decreases the risk cardiovascular disease,<ref name="pmid28301692">{{cite journal | vauthors = Al-Khudairy L, Flowers N, Wheelhouse R, Ghannam O, Hartley L, Stranges S, Eres K | title = Vitamin C supplementation for the primary prevention of cardiovascular disease | journal = The Cochrane Database of Systematic Reviews | volume = 2017 | pages = CD011114 | date = March 2017 | issue = 3 | pmid = 28301692 | doi = 10.1002/14651858.CD011114.pub2 | pmc = 6464316 }}</ref> although there may be an association between higher circulating vitamin C levels or dietary vitamin C and a lower risk of stroke.<ref name="pmid24284213">{{cite journal | vauthors = Chen GC, Lu DB, Pang Z, Liu QF | title = Vitamin C intake, circulating vitamin C and risk of stroke: a meta-analysis of prospective studies | journal = J Am Heart Assoc | volume = 2 | issue = 6 | pages = e000329 | date = November 2013 | pmid = 24284213 | pmc = 3886767 | doi = 10.1161/JAHA.113.000329 }}</ref> There is a positive effect of vitamin C on [[endothelial dysfunction]] when taken at doses greater than 500&nbsp;mg per day. (The endothelium is a layer of cells that line the interior surface of blood vessels.)<ref name="pmid24792921">{{cite journal | vauthors = Ashor AW, Lara J, Mathers JC, Siervo M | title = Effect of vitamin C on endothelial function in health and disease: a systematic review and meta-analysis of randomized controlled trials | journal = Atherosclerosis | volume = 235 | issue = 1 | pages = 9–20 | date = July 2014 | pmid = 24792921 | doi = 10.1016/j.atherosclerosis.2014.04.004 }}</ref>

===Blood pressure===
Serum vitamin C was reported to be 15.13 μmol/L lower in people with [[hypertension]] compared to normotensives. The vitamin was inversely associated with both [[systolic blood pressure]] (SBP) and [[diastolic blood pressure]] (DBP).<ref name="pmid32426036">{{cite journal |vauthors=Ran L, Zhao W, Tan X, Wang H, Mizuno K, Takagi K, Zhao Y, Bu H |title=Association between serum vitamin C and the blood pressure: A systematic review and meta-analysis of observational studies |journal=Cardiovasc Ther |volume=2020 |issue= |pages=4940673 |date=April 2020 |pmid=32426036 |pmc=7211237 |doi=10.1155/2020/4940673 |url= | doi-access = free | title-link = doi }}</ref> Oral supplementation of the vitamin resulted in a very modest but statistically significant decrease in SBP in people with hypertension.<ref name=Guan2020>{{cite journal |vauthors=Guan Y, Dai P, Wang H |title=Effects of vitamin C supplementation on essential hypertension: A systematic review and meta-analysis |journal=Medicine (Baltimore) |volume=99 |issue=8 |pages=e19274 |date=February 2020 |pmid=32080138 |pmc=7034722 |doi=10.1097/MD.0000000000019274 |url=}}</ref><ref name=Llban2023>{{cite journal |vauthors=Lbban E, Kwon K, Ashor A, Stephan B, Idris I, Tsintzas K, Siervo M |title=Vitamin C supplementation showed greater effects on systolic blood pressure in hypertensive and diabetic patients: an updated systematic review and meta-analysis of randomized clinical trials |journal=Int J Food Sci Nutr |volume=74 |issue=8 |pages=814–25 |date=December 2023 |pmid=37791386 |doi=10.1080/09637486.2023.2264549 |s2cid=263621742 |url=https://figshare.com/articles/journal_contribution/24241426 |access-date=December 23, 2023 |archive-date=January 21, 2024 |archive-url=https://web.archive.org/web/20240121044305/https://figshare.com/articles/journal_contribution/Vitamin_C_supplementation_showed_greater_effects_on_systolic_blood_pressure_in_hypertensive_and_diabetic_patients_an_updated_systematic_review_and_meta-analysis_of_randomised_clinical_trials/24241426 |url-status=live }}</ref> The proposed explanation is that vitamin C increases intracellular concentrations of [[tetrahydrobiopterin]], an endothelial [[nitric oxide synthase]] cofactor that promotes the production of [[nitric oxide]], which is a potent vasodilator. Vitamin C supplementation might also reverse the nitric oxide synthase inhibitor [[NG-monomethyl-L-arginine|NG-monomethyl-L-arginine 1]], and there is also evidence cited that vitamin C directly enhances the biological activity of nitric oxide<ref name=Guan2020 />

===Type 2 diabetes===
There are contradictory reviews. From one, vitamin C supplementation cannot be recommended for management of [[type 2 diabetes]].<ref name="mason">{{cite journal |vauthors=Mason SA, Keske MA, Wadley GD |title=Effects of vitamin C supplementation on glycemic control and cardiovascular risk factors in people With type 2 diabetes: A GRADE-assessed systematic review and meta-analysis of randomized controlled trials |journal=Diabetes Care |volume=44 |issue=2 |pages=618–30 |date=February 2021 |pmid=33472962 |doi=10.2337/dc20-1893 |url=https://diabetesjournals.org/care/article/44/2/618/35482/Effects-of-Vitamin-C-Supplementation-on-Glycemic |doi-access=free |title-link=doi |hdl=10536/DRO/DU:30147432 |hdl-access=free |access-date=December 21, 2023 |archive-date=January 21, 2024 |archive-url=https://web.archive.org/web/20240121044253/https://diabetesjournals.org/care/article/44/2/618/35482/Effects-of-Vitamin-C-Supplementation-on-Glycemic |url-status=live }}</ref> However, another reported that supplementation with high doses of vitamin C can decrease [[Glucose test|blood glucose]], [[insulin]] and [[Glycated hemoglobin|hemoglobin A1c]].<ref name="nos">{{cite journal |vauthors=Nosratabadi S, Ashtary-Larky D, Hosseini F, Namkhah Z, Mohammadi S, Salamat S, Nadery M, Yarmand S, Zamani M, Wong A, Asbaghi O |title=The effects of vitamin C supplementation on glycemic control in patients with type 2 diabetes: A systematic review and meta-analysis |journal=Diabetes and Metabolic Syndrome |volume=17 |issue=8 |pages=102824 |date=August 2023 |pmid=37523928 |doi=10.1016/j.dsx.2023.102824 |s2cid=259581695 }}</ref>

=== Iron deficiency ===
One of the causes of [[iron-deficiency anemia]] is reduced absorption of iron. Iron absorption can be enhanced through ingestion of vitamin C alongside iron-containing food or supplements. Vitamin C helps to keep iron in the reduced ferrous state, which is more soluble and more easily absorbed. It also [[chelate]]s iron into a soluble complex.<ref name="pmid28189173">{{cite journal | vauthors = DeLoughery TG | title = Iron Deficiency Anemia | journal = The Medical Clinics of North America | volume = 101 | issue = 2 | pages = 319–332 | date = March 2017 | pmid = 28189173 | doi = 10.1016/j.mcna.2016.09.004 | type = Review }}</ref> It specifically helps the absorption of non-heme iron,<ref>{{cite journal | vauthors = Heffernan A, Evans C, Holmes M, Moore J |title=The Regulation of Dietary Iron Bioavailability by Vitamin C: A Systematic Review and Meta-Analysis |journal=Proceedings of the Nutrition Society |date=2017 |volume=76 |issue=OCE4 |doi=10.1017/S0029665117003445}}</ref> which is found in non-meat sources and absorbed via [[DMT1]].<ref name="pmid28189173"/>

===Alzheimer's disease===
Lower plasma vitamin C concentrations were reported in people with [[Alzheimer's disease]]. Reviews do not present reporting on supplement intervention clinical trials.<ref>{{cite journal | vauthors = Harrison FE | title = A critical review of vitamin C for the prevention of age-related cognitive decline and Alzheimer's disease | journal = Journal of Alzheimer's Disease | volume = 29 | issue = 4 | pages = 711–26 | year = 2012 | pmid = 22366772 | pmc = 3727637 | doi = 10.3233/JAD-2012-111853 }}</ref><ref>{{cite journal |vauthors=Hamid M, Mansoor S, Amber S, Zahid S |title=A quantitative meta-analysis of vitamin C in the pathophysiology of Alzheimer's disease |journal=Front Aging Neurosci |volume=14 |issue= |pages=970263 |date=2022 |pmid=36158537 |pmc=9490219 |doi=10.3389/fnagi.2022.970263 |doi-access=free |url=}}</ref>

===Eye health===
Higher dietary intake of vitamin C was associated with lower risk of age-related cataracts.<ref name="pmid30878580">{{cite journal |vauthors=Sideri O, Tsaousis KT, Li HJ, Viskadouraki M, Tsinopoulos IT |title=The potential role of nutrition on lens pathology: a systematic review and meta-analysis |journal=Surv Ophthalmol |volume=64 |issue=5 |pages=668–78 |date=2019 |pmid=30878580 |doi=10.1016/j.survophthal.2019.03.003 |s2cid=81981938 |url=}}</ref><ref>{{cite journal |vauthors=Jiang H, Yin Y, Wu CR, Liu Y, Guo F, Li M, Ma L |title=Dietary vitamin and carotenoid intake and risk of age-related cataract |journal=Am J Clin Nutr |volume=109 |issue=1 |pages=43–54 |date=January 2019 |pmid=30624584 |doi=10.1093/ajcn/nqy270 |url=|doi-access=free }}</ref> Vitamin C supplementation did not prevent age-related macular degeneration.<ref>{{cite journal |vauthors=Evans JR, Lawrenson JG |title=Antioxidant vitamin and mineral supplements for preventing age-related macular degeneration |journal=Cochrane Database Syst Rev |volume=2017 |issue=7 |pages=CD000253 |date=July 2017 |pmid=28756617 |pmc=6483250 |doi=10.1002/14651858.CD000253.pub4 |url=}}</ref>

===Periodontal disease===
Low intake and low serum concentration were associated with greater progression of [[periodontal disease]].<ref name="pmid38245765">{{cite journal |vauthors=Mi N, Zhang M, Ying Z, Lin X, Jin Y |title=Vitamin intake and periodontal disease: a meta-analysis of observational studies |journal=BMC Oral Health |volume=24 |issue=1 |pages=117 |date=January 2024 |pmid=38245765 |pmc=10799494 |doi=10.1186/s12903-024-03850-5 |doi-access=free |url=}}</ref><ref name="pmid31336735">{{cite journal |vauthors=Tada A, Miura H |title=The relationship between vitamin C and periodontal diseases: A systematic review |journal=Int J Environ Res Public Health |volume=16 |issue=14 |date=July 2019 |page=2472 |pmid=31336735 |pmc=6678404 |doi=10.3390/ijerph16142472 |doi-access=free |url=}}</ref>