Vitamin C Simply Explained

1. What Is Vitamin C?

Vitamin C is a water-soluble vitamin. Chemically it is called L-ascorbic acid. The body cannot produce it itself. Therefore we must take it in through food. It became known through scurvy. That was a disease of sailors who ate no fresh fruit and vegetables for a long time. Today many take it as a dietary supplement, for example for colds.

2. Where Is It Found, and What Is It Made From?

Vitamin C is found in fresh fruit and vegetables. It is particularly abundant in citrus fruits, peppers, kiwi, berries and potatoes. In the body it occurs in all cells. The concentration is particularly high in the adrenal glands and in white blood cells. For dietary supplements, vitamin C is produced technically from glucose. It is mostly present as ascorbic acid or as ascorbate salt.

3. What Does Vitamin C Do? What Research Shows

Sepsis and Critical Care

In blood poisoning and in the intensive care unit, the results are mixed. Some reviews found lower mortality with vitamin C, especially as an infusion 29101321. Others found no significant difference 61216. In septic shock, there was no survival benefit 617. The largest single study saw death or persistent organ failure combined even more frequently with vitamin C than with placebo (sham treatment) 36. The administration of circulatory drugs was shorter 612131621, the length of stay in the intensive care unit did not change 12161721.

Oxidative Stress and Antioxidant Status

In oxidative stress and antioxidant status, the results are mixed. Some studies found higher antioxidant capacity after vitamin C 4355. Inflammation markers in the blood decreased in several studies, for example in lung failure (ARDS) 47 and in sepsis 44. Also in healthy individuals with low vitamin C levels, inflammation and stress markers in the blood decreased compared with placebo 57. In moderate pancreatitis, the inflammation marker CRP decreased more with vitamin C infusions than with placebo 38. Other studies found no difference in inflammatory messengers 50 or in the inflammation marker CRP 39. Isoprostanes, a measure of oxidative stress, did not change with vitamin C infusions in septic shock 48.

Skin and Connective Tissue

In second-degree burns, a vitamin C solution on the skin accelerated healing in a small study 52. A review on perioperative care describes slightly better wound healing 26. In melasma (dark spots on the face), vitamin C for application was more effective than placebo in a pooled analysis of many studies 31. After treatment with fine needles (microneedling), the spots improved with vitamin C similarly to tranexamic acid; there was no untreated group 54. In Bateman purpura (bruises on thin aged skin), vitamin C for application improved skin appearance, skin thickness and elasticity compared with the untreated side 56. After wisdom tooth removal, pain and swelling on the second day were less than with placebo 46.

Common Cold and Respiratory Infections

Regularly taken vitamin C shortened colds in placebo studies, more clearly in children than in adults 34. An extra dose at the start of a cold shortened the duration and relieved fever 33; another study found no difference when taken only from the start of a cold 37. In a study on recruits, the frequency of a cold diagnosis decreased 35. In children with pneumonia, vitamin C improved severity, but not hospital stay 40. In COVID-19, a meta-analysis saw lower mortality, which still needs confirmation 2; two others found no difference 1123.

Immune Function

In severe infections and sepsis, a review describes favorable effects on the immune response, but no consistent clinical benefit 28. A small preliminary study in septic shock found more neutrophils (certain white blood cells) in the blood after vitamin C infusions than with placebo 49. A study in healthy individuals showed that a liposomal preparation (vitamin C in tiny fat bubbles) is better absorbed into the blood and into the white blood cells than standard vitamin C 53. No difference was shown in the defense reaction of donor cells against the body after a stem cell transplantation 51.

Iron Absorption from Food

In young children, an ascorbic acid addition to iron-zinc sprinkles did not change iron absorption 45. In anemia due to iron deficiency, the hemoglobin value (red blood pigment) increased more under plant iron with and without vitamin C than under placebo 42. Whether the vitamin C addition provides its own benefit remains open. The strength of evidence is unclear because only one small study tested the vitamin C addition alone.

Other Investigations

In this area, many studies on very different questions have been conducted. The results are mixed. In intensive care patients overall, a review reported lower overall mortality with vitamin C, but this is not yet considered secured 2; an older one found no difference 19. In type 2 diabetes, two reviews found better values for long-term blood sugar and fasting blood sugar 1430. For cancer prevention, a review of large studies found no difference 1.

4. How Was Vitamin C Taken in the Studies?

In the studies, vitamin C was mostly taken as a tablet, capsule or powder. There were also infusions into the vein. In addition, sodium ascorbate and preparations for application to the skin were used. Individual studies tested liposomal preparations and ascorbyl palmitate. The doses, the duration and the comparison groups were very different.

5. Is Vitamin C Safe? Side Effects in the Studies

With very high or repeated doses, kidney damage from oxalate deposits has been described, and in a congenital enzyme deficiency (G6PD deficiency) also a breakdown of red blood cells 2425. After liver transplantation, kidney failure occurred more frequently with ascorbic acid than with placebo in a small study 50. A meta-analysis saw more adverse events 7; others found no increased ones, also not for the mixture with thiamine and hydrocortisone 9815. Occasionally nausea, vomiting, low blood pressure and palpitations were mentioned 27. Mixed preparations with other substances do not allow conclusions about vitamin C alone.

All details with tables and sources: full expert page on Vitamin C