Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin found particularly in citrus fruits and green vegetables. One of its roles is as an antioxidant, that is, it helps to protect cells from damage by oxidative stress and also improves mitochondrial function. Another role is as a cofactor for several enzymes. After absorption, Vitamin C is present throughout the whole body.

Large cross-sectional population studies confirm that vitamin C deficiency is common in humans, affecting 5%–10% of adults in the industrialized world. Moreover, significant associations between poor vitamin C status and increased morbidity and mortality have consistently been observed. However, the absorption, distribution and elimination kinetics of vitamin C in vivo are highly complex, due to dose-dependent non-linearity, and the specific regulatory mechanisms are not fully understood. Several studies indicates the recovery from Vitamin C depletion will require several months of treatment.

Homeostasis
Vitamin C is ingested, absorbed from the intestinal lumen and transported to various peripheral organs with the blood. Finally, vitamin C is excreted in the renal glomeruli and reabsorbed through the tubular systems. Tissue concentrations are dependent on all of these processes. Vitamin C is found in the whole body, even skin tissue. Vitamin C is also found in bone marrow, and bone marrow is probably also involved in the vitamin C homeostasis process.

Function
Vitamin C is found in various parts in the body. High levels of vitamin C are found in the eyes, pituitary, adrenal gland, pancreas, liver, spleen and brain. Vitamin C is also found in relative high levels in the bone marrow, muscles and skin. It is important in mast cell activation disorder for its role in the breakdown of histamine and as a mast cell stabilizer. Vitamin C is also a co-factor in collagen synthesis, making it a potentially important nutrient in Ehlers-Danlos syndrome and other connective tissue disorders. Deficiency of vitamin C may contribute to osteoporosis.

Delivery of nutrients to the skin. The location of the vitamin C transport proteins SVCT1 and SVCT2 are indicated. Red arrows depict nutrient flow from the blood vessels in the dermis to the epidermal layer. Nutrients delivered by topical application would need to penetrate the barrier formed by the the outer layer of the skin, called the stratum corneum.

Adrenal gland
The adrenal gland can inject vitamin C into the blood.

Depletion
Several studies indicates the recovery from Vitamin C depletion will require several months of treatment. Vitamin C concentrations in plasma and circulating cells were studied in young healthy men and women  each of whom were given six to seven different doses of the vitamin in two depletion-repletion studies. Seven healthy men (4A) and fifteen healthy women (4B), all nonsmokers, age 19-27 years were studied as inpatients. To decrease hospitalization time, outpatient subjects prior to admission were instructed to consume a diet containing < 60 mg of vitamin C. When inpatients, throughout hospitalization they consumed a defined diet containing less than 5 mg of vitamin C daily. Deficiencies of other nutrients were prevented by supplementation. When plasma vitamin C concentrations achieved nadir of <10 µM, vitamin C in solution was administered at 15 mg orally in the fasted state twice daily (30 mg total per day) until steady state for the dose was achieved.

ME/CFS
Dr. Rosamund Vallings, an ME/CFS expert, warns against very high dose mega vitamin C supplementation, stating that: "those with CFS...maybe worsened by high dose vitamin C, as the immune system is often already very overactive, and Vitamin C may aggravate this condition."

Skin tissue
Too much sun exposure may deplete the Vitamin C stores in the skin tissue.

Osteoporosis
Longer periods of Vitamin C deficiency may lead to osteoporosis.

Mast cell activation disorder
Numerous studies have found Vitamin C to be inversely correlated with histamine and that the administration of Vitamin C reduces blood histamine levels. It does this potentially through several mechanisms: by inhibiting mast cell production; by increasing diamine oxidase (an enzyme that breaks down histamine); by inhibiting mast cell degranulation and the release of histamine in the first place (i.e., as a mast cell stabilizer), and by inhibiting histidine decarboxylase (the enzyme that forms histamine).

Blood tests
Low blood concentration of ascorbic acid may lead to lassitude. From.

On blood test procedure: cited from abstract of : "This chapter describes the analysis of ascorbic acid and dehydroascorbic acid in biological samples. The chapter focuses on ascorbate assays because these techniques are substantially more advanced than those for dehydroascorbic acid and most techniques for the latter are based on those of the former. High performance liquid chromatography (HPLC) with electrochemical (EC) detection is the ascorbate assay technique that provides the highest sensitivity, specificity, and accounts for substance interference. The general separation principles of HPLC are utilized to separate ascorbate from other substances. A mobile phase—or the solution for chromatography—is selected that optimizes both separation and detection. Once separation is accomplished, ascorbate is detected by one of two distinct types of EC detectors, amperometric EC detectors, or coulometric detectors. The principle of both detectors is that they pass a voltage across an area. Current generated by the voltage and the components of the mobile phase are measured. Amperometric EC detectors are “flow by” detectors, in which the solution containing ascorbate and the components of the mobile phase for HPLC separation flow around the detector. Coulometric detectors are “flow through” detectors. The mobile phase and ascorbate flow through the detector, which is porous. Coulometric detectors are preferred over amperometric detectors. The chapter concludes with a discussion of the detection of radiolabeled ascorbate and dehydroascorbic acid."

Notable studies

 * 2014, Mitochondrial dysfunction and chronic disease: treatment with natural supplements (Full text)

Learn more

 * Linus Pauling Institute Micronutrient Information Center - Vitamin C