Vitamin C

We evaluated 252 human studies on Vitamin C, including 160 randomised controlled trials and 63 meta-analyses or systematic reviews; the controlled studies include 26,210 participants in total. As of 13 October 2026.

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1. What Is Vitamin C? Occurrence, Origin and Forms

Vitamin C is a water-soluble vitamin, chemically L-ascorbic acid. The human body cannot make it and depends on dietary intake. It became known through the link between vitamin C deficiency and scurvy, the disease that affected sailors on long voyages without fresh fruit and vegetables; today it is taken mainly as a dietary supplement, for example during colds.

Vitamin C occurs in fresh fruit and vegetables, especially in citrus fruits, peppers, kiwi, berries and potatoes. In the body it is found in all cells, in high concentration in the adrenal glands and in white blood cells.

For dietary supplements, vitamin C is produced industrially from glucose and is usually supplied as ascorbic acid or as an ascorbate salt. Studies examine mainly the oral intake of ascorbic acid or sodium ascorbate, liposomal preparations and intravenous administration.

Forms and Preparations Studied

• L-ascorbic acid (pure form)
• Sodium ascorbate and calcium ascorbate (salts, less acidic)
• Ascorbyl palmitate (fat-soluble)
• Liposomal preparations
• Oral intake as tablet, capsule, powder or drink
• Intravenous administration as an infusion

Not covered on this page:

• D-isoascorbic acid (erythorbic acid, E 315), a related substance without vitamin C activity
• Multivitamin preparations and combinations with other substances (e.g. zinc, vitamin D)
• Preparations from vitamin C-rich fruits such as acerola, rose hip or sea buckthorn; a study on these is not a study on isolated vitamin C
• Ascorbic acid as a technical antioxidant and preservative in foods (E 300)

2. What Does Vitamin C Do? Results by Area

How to read the table: counted are human studies whose results concern the area. “High” means at least one meta-analysis and two controlled studies showing improvement, or at least three controlled studies of which three quarters show improvement, with at least 300 participants in total. “Moderate” means at least two controlled studies showing improvement, as a majority, or one meta-analysis alongside controlled studies. “Low” means one controlled study showing improvement. Where an area has no controlled study, the strength of evidence is at most “low” (result “reviews only” or “observational data only”). Everything else is “unclear”. A study counts as showing improvement when at least half of its outcomes in this area improved. Reviews of combination products do not count as meta-analyses; results that only describe side effects or shares of users do not count as an effect. The same study is counted only once.

3. What the Studies Show in Detail

Vitamin C, Sepsis and Critical Care: Human Studies

In sepsis and intensive care, the studies show a mixed picture with high certainty of evidence. Meta-analyses found a lower mortality with vitamin C, especially intravenously and without adjunctive agents 412131931, which, however, still needs to be confirmed. Other meta-analyses found overall no confirmed difference 81622, and in septic shock no survival benefit 824. Whether high or lower doses are more favorable is answered in opposite ways by two meta-analyses 1219. In the largest single study, death or persistent organ failure combined occurred more often with intravenous vitamin C than with placebo 62. The administration of circulatory agents (vasopressors) was shorter with intravenous vitamin C 816192231, the length of stay in the intensive care unit did not change 16222431. The mixture of vitamin C, thiamine and hydrocortisone shortened the vasopressor duration and lowered the SOFA score in meta-analyses 1121, but not the short-term mortality 21. These findings belong to the mixture, not to vitamin C alone. Predominantly intravenous preparations were investigated, in addition sodium ascorbate; the optimal dose, the timing and which patient groups benefit remain open.

Further studies in this area: 13 14 16 17 18 19 22 23 24 31 32 39 40 46 49 62 63 72 77 78 84 85 87 95 96 99 100 105 107 115 118 119 120 124 128 134 155 157 159 167 168 169 171 176 178 181 182 183 184 186 187

Vitamin C, Oxidative Stress and Antioxidant Status: Human Studies

For oxidative stress and antioxidant status, the studies on vitamin C show a mixed picture with high certainty of evidence. A randomized controlled study found a higher antioxidant capacity after vitamin C administration during cardiopulmonary bypass 93. In overweight individuals, it rose more strongly after vitamin C added to a sugar solution than without 137. Inflammation markers fell compared with the control in several randomized studies, for example IL-8 in ARDS 116 and a TNF receptor in sepsis 95. In healthy individuals with low vitamin C status, isoprostanes, IL-6 and TNF-α fell compared with placebo 146. In moderate pancreatitis, CRP fell more strongly than with placebo 76; after joint replacement, a meta-analysis found lower CRP and IL-6 values on the first day 28. Other randomized controlled studies found no difference in cytokines 121 or in CRP 78. A systematic review on knee prosthesis found inconsistent results for inflammation markers 25; in septic shock, CRP and myeloperoxidase remained the same compared with placebo 118. Isoprostanes did not change with parenteral vitamin C compared with placebo 117. Mixtures of vitamin C and vitamin E lowered malondialdehyde and ROS in endometriosis 35 and, in sarcopenia, malondialdehyde compared with placebo, while glutathione rose 103. In a randomized study in septic shock with separate arms for vitamin C, vitamin E, N-acetylcysteine and melatonin, lipid peroxidation fell in each arm compared with the baseline value 84. The mixture of vitamin C and chromium improved blood lipids in type 2 diabetes compared with placebo; the contribution of vitamin C remains open 104. The investigations predominantly concerned ill or inadequately supplied people; the transferability to well-supplied individuals and the comparison of form, dose and administration remain open.

Further studies in this area: 88 93 95 116 117 118 120 121 133 137 139 140 143 145 146 147 155 156 158 163 164 179 186

Vitamin C, Skin and Connective Tissue: Human Studies

In second-degree burns, a topical vitamin C solution accelerated epithelialization in a small randomized study 129; a systematic review on perioperative care describes slightly better wound healing 42. In melasma, topical vitamin C was among the more effective treatments versus placebo in a network meta-analysis 50. After microneedling, melasma improved with vitamin C as with tranexamic acid compared with baseline 135. In Bateman purpura of aged skin, topical vitamin C improved skin appearance, skin thickness and elasticity compared with the untreated side 141. After wisdom tooth removal, pain and swelling on the second day were less than with placebo, wound healing did not differ with certainty 106. Vitamin C injections after flexor tendon repair showed no certain difference 126. A mixture of collagen and vitamin C, sometimes with hyaluronic acid, improved dermal density and wrinkles compared with placebo; the contribution of vitamin C remains open 92. Statements on dose-response relationships, on transferability to well-nourished individuals and on long-term effects remain open.

Further studies in this area: 135 141 142 143 165 180 183

Vitamin C, Common Cold and Respiratory Infections: Human Studies

Regularly taken vitamin C shortened colds in placebo studies, more clearly in children than in adults 55; an additional dose at the onset of a cold shortened the duration and alleviated fever 54. In a randomized controlled trial with recruits, the frequency of a cold diagnosis decreased 58, as it did in a placebo study over the winter 161. In adults with atrophic gastritis, there were fewer colds at a higher dose, but not shorter ones 74. In children with pneumonia, vitamin C improved the severity compared with placebo, but not the length of hospital stay 81. In ARDS, intravenous vitamin C in an open randomized trial improved oxygen supply and weaning from the ventilator compared with standard treatment 116. In COVID-19, a meta-analysis saw lower mortality, which still needs to be confirmed 4; two other meta-analyses found no difference 1538. The strength of evidence is high, supported by several meta-analyses and randomized controlled trials; however, the individual studies are mixed. However, forms, doses, duration, comparison groups and the baseline status of participants differ considerably; for well-supplied individuals without deficiency, the transferability is open. As an addition to antiviral therapy, vitamin C in a meta-analysis of Chinese studies shortened the time to improvement compared with antiviral therapy alone 52. A randomized trial found no difference in duration or severity compared with a very low vitamin C dose when taken from the onset of a cold 70. In COVID-19, high-dose ascorbic acid alone did not shorten the symptom duration 75. Mixtures with zinc 91 and the preparation ArtemiC made of artemisinin, curcumin, frankincense and vitamin C 110 do not allow conclusions about vitamin C alone.

Further studies in this area: 75 81 159 161 183 187

Vitamin C and Immune Function: Human Studies

In severe infections and sepsis, a systematic review describes individual studies with favorable effects on the immune response, but no consistent clinical benefit 46. A small randomized controlled pilot study in septic shock found higher neutrophil counts with intravenous L-ascorbic acid than with placebo 118. A randomized controlled study in healthy individuals found better uptake into plasma and white blood cells for a liposomal preparation than for standard vitamin C 132. No difference was shown in acute graft-versus-host disease after stem cell transplantation with intravenous, then oral L-ascorbic acid 125. Larger studies with immune measures as the primary aim are still pending.

Vitamin C and Iron Absorption from Food: Human Studies

In young children, an ascorbic acid addition to iron-zinc sprinkles did not change iron absorption in a randomized controlled trial 98. In iron deficiency anemia, hemoglobin increased more under plant iron with vitamin C from amla and under iron alone than under placebo 90. Whether the vitamin C addition provides its own benefit remains open. The strength of evidence is unclear: only one small controlled trial tested the vitamin C addition alone, a meta-analysis is lacking.

Vitamin C: Further Outcomes in Studies

In this area, many controlled trials and meta-analyses have been conducted on very different questions; the strength of evidence is high, but the results are mixed. In intensive care patients overall, a meta-analysis saw lower overall mortality with oral or intravenous administration, which is not yet secured 4; an older meta-analysis found no difference 27. In type 2 diabetes, two meta-analyses found better values for long-term blood sugar and fasting blood sugar 2048. After gallbladder surgery, high-dose oral vitamin C did not alleviate pain 71; after joint replacement, according to a meta-analysis, it reduced morphine consumption, but not pain scores 28. For cancer prevention, a meta-analysis of large studies found no difference 3. Statements on precisely defined dosages, on transferability to well-supplied individuals, and on forms such as sodium ascorbate, calcium ascorbate, ascorbyl palmitate and liposomal preparations remain open.

Further studies in this area: 26 27 28 29 33 34 36 38 39 41 42 43 44 45 48 51 53 60 64 68 71 73 76 79 80 82 83 89 93 94 97 99 101 102 106 108 109 111 112 113 114 116 121 123 125 128 130 131 133 136 138 139 144 145 146 147 148 149 150 151 152 153 154 156 160 162 163 166 169 170 172 173 174 175 177 179 183 184 185 188 189

4. How Is Vitamin C Dosed? Preparation, Dose and Duration in Studies

The studies predominantly used oral L-ascorbic acid as a tablet, capsule or powder as well as intravenous infusions, in addition sodium ascorbate and topical preparations. Individual controlled studies tested liposomal preparations and ascorbyl palmitate. The doses, durations and comparison groups differ considerably between the studies.

5. Is Vitamin C Safe? Side Effects in Studies

Meta-analyses found no increased adverse events with intravenous vitamin C 12 and with the mixture with thiamine and hydrocortisone 1121. Another meta-analysis, by contrast, saw more adverse events 9. Nausea, vomiting, hypotension and tachycardia were mentioned occasionally 45. Reviews describe oxalate nephropathy and hemolysis in G6PD deficiency at very high or repeated doses 3940. After liver transplantation, kidney failure occurred more often with ascorbic acid than with placebo in a small study 121.

6. What Remains Open: Limits of the Evidence

• The optimal dose, the timing and the duration of administration are open for most areas.
• The transferability to well-supplied individuals without deficiency is not clarified.
• Many studies investigated combination preparations whose findings cannot be attributed to vitamin C alone.
• Long-term effects and dose-response relationships are hardly studied.
• The comparison of different vitamin C forms (ascorbic acid, sodium ascorbate, liposomal form) with one another is still largely pending.

7. Bottom Line: What Is Established About Vitamin C

Vitamin C is an essential water-soluble vitamin that the body cannot produce itself. Human studies show benefits for colds, especially a shorter duration with regular intake, and indications from small studies of better wound and skin healing. For oxidative stress and inflammation, the results are mixed: some studies found lower inflammation markers, others no difference. In sepsis, the picture is inconsistent: some meta-analyses report a lower mortality, others no difference, and the largest single study saw rather disadvantages. Combination preparations with other substances do not allow a conclusion about vitamin C alone. The tolerability is considered predominantly good; at very high doses, oxalate nephropathy and hemolysis in G6PD deficiency are described.