Vitamin C levels

Vitamin C is a water-soluble vitamin, an antioxidant and an essential cofactor for collagen biosynthesis, carnitine and catecholamine metabolism and dietary iron absorption.

Vitamin C or ascorbic acid is a water-soluble vitamin essential for optimal growth and development. Humans are unable to synthesize vitamin C, so it is obtained strictly through dietary intake of fruits and vegetables. Citrus fruits, berries, tomatoes, potatoes and green leafy vegetables are excellent sources of vitamin C.

Ascorbic acid functions as a cofactor, enzyme complement, cosubstrate and potent antioxidant in various metabolic reactions and processes. It also stabilizes vitamin E and folic acid and improves iron absorption. It neutralizes free radicals and toxins and attenuates inflammatory response, including sepsis syndrome.

With respect to collagen (fundamental to skin, tendons, ligaments and blood vessels), the proline residues of procollagen require vitamin C for hydroxylation, which makes it necessary for the formation of the triple helix of mature collagen. The lack of a stable triple helix structure compromises the integrity of skin, mucous membranes, blood vessels and bones. Consequently, a vitamin C deficiency results in scurvy, which presents with hemorrhage, hyperkeratosis and hematological abnormalities.

Vitamin C deficiency can occur due to reduced intake or increased requirements or losses due to medical pathologies or mutations. This can influence the risk of certain diseases differently for each individual and can make a difference in the minimum necessary amount of vitamin C that needs to be consumed each day. People at risk of inadequate intake of the vitamin include patients in the following groups:

  • The elderly
  • Those suffering from an alcohol use disorder, anorexia or cancer
  • Those who practice dietary fads
  • Those with suspected food allergies
  • Those receiving unsupplemented parenteral nutrition
  • Those on restricted diets secondary to inflammatory bowel disease, gastrointestinal reflux or Whipple's disease
  • Those who smoke tobacco products
  • Those taking medications such as aspirin, indomethacin, oral contraceptives, tetracyclines, and corticosteroids
  • Those who have kidney failure due to leaching of water-soluble vitamin C during dialysis
  • Those who have a complication of interleukin 2 treatment of metastatic renal cell carcinoma
  • Those receiving liver transplants

Serum vitamin levels can be affected by both environmental factors, such as diet, as well as genetic factors, such that mutations affecting some process of vitamin metabolism or transport can be inherited. One of the most recent genome-wide meta-analyses involving 52,000 people of European ancestry has identified 11 markers associated with variability in plasma vitamin C levels. Some of the most significant markers belong to genes such as SLC23A1 and SLC23A3, responsible for producing sodium-dependent vitamin C transporters, or the RER1 gene involved in vitamin C metabolism.

Number of observed variants

13.5 million variants

Number of loci analyzed in the study

11 loci


Zheng J.S., Luan J., et al. Plasma Vitamin C and Type 2 Diabetes: Genome-Wide Association Study and Mendelian Randomization Analysis in European Populations. Diabetes Care, 17 Nov 2020, 44(1):98-106

Muhammad A., Jamil R.T., et al. (2022) Vitamin C (Ascorbic Acid). StatPearls

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