Vitamin C

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Vitamin C (ascorbic acid) functions as a cofactor for enzymes involved in the biosynthesis of collagen, carnitine, and norepinephrine[1]. In addition, it acts as a powerful antioxidant, quenching reactive oxygen species and reactive nitrogen species[2], as well as being the first line of defense against oxygen radicals in the water-soluble component[3].

Unlike humans, ascorbic acid is not an essential vitamin in dogs since it is synthesized by the liver. Humans, guinea pigs and flying mammals lack L-gulono-γ -lactone oxidase, the final enzyme in the biosynthesis of ascorbic acid from glucose[4].

Similar to other antioxidants such as N-acetylcysteine and α-tocopherol, the greatest requirements for vitamin C are observed in young dogs[5], geriatric patients[6] and those with serious illness.

Oral supplementation does not significantly alter blood or tissue levels of this anti-oxidant and has only minor effects on antioxidant and immunological functions[7]. Excess ascorbic acid is reversibly oxidized to dehydroascorbic acid in the body[8] and administration of even high doses of intravenous vitamin C are maintained for only 4 - 6 hours before returning to normal levels[9].

In dogs, the normal blood levels are 3.2 - 8.9 mg/L[10].

Levels of vitamin C commonly increased during periods of physical or emotional stress or disease, such as during hospitalization at a veterinary center[11].

Vitamin C supplementation may be warranted during severe physical trauma (e.g. motor vehicle accidents or burns)[12], toxin ingestion, acute renal injury[13], polyarthritis[14], following orthopedic procedures, when using constrast dyes associated with excretory urography[15] and post-operative renal transplantation[16].

This vitamin does not significantly improve clinical recovery in cases of portosystemic shunt[17], chronic renal disease[18], lymphoma[19] or infertility[20].

Supplementation, if required, can be given at 5 - 10 mg/kg daily.

References

  1. Padh H (1991) Vitamin C: newer insights into its biochemical functions. Nutr Rev 49:65–70
  2. Frei B et al (1989) Ascorbate is an outstanding antioxidant in human blood plasma. Proc Natl Acad Sci U S A 86:6377–6381
  3. Nordberg J & Arner ES (2001) Reactive oxygen species, antioxidants, and the mammalian thioredoxin system. Free Radic Biol Med 31:1287–1312
  4. Nishikimi M et al (1994) Cloning and chromosomal mapping of the human nonfunctional gene for L-gulono-γ -lactone oxidase, the enzyme for L-ascorbic acid biosynthesis missing in man. J Biol Chem 269:13685–13688
  5. Ogawa E (2008) Age-dependent changes in uptake and recycling of ascorbic acid in erythrocytes of Beagle dogs. J Comp Physiol B 178(6):699-704
  6. Hall JA et al (2006) Dietary antioxidants and behavioral enrichment enhance neutrophil phagocytosis in geriatric Beagles. Vet Immunol Immunopathol 113(1-2):224-233
  7. Hesta M et al (2009) The effect of vitamin C supplementation in healthy dogs on antioxidative capacity and immune parameters. J Anim Physiol Anim Nutr (Berl) 93(1):26-34
  8. McDowell LR (1989) Vitamin C: Vitamins in Animal Nutrition. San Diego: Academic Press. pp:365–387
  9. Scott KC et al (2002) Serum ascorbic acid concentrations in previously unsupplemented greyhounds after administration of a single dose of ascorbic acid intravenously or per os. J Anim Physiol Anim Nutr (Berl) 86(7-8):222-228
  10. Hishiyama N et al (2006) Plasma concentration of vitamin C in dogs with a portosystemic shunt. Can J Vet Res 70(4):305-307
  11. Groth E et al (2012) Hyperascorbaemia in dogs admitted to a teaching hospital intensive care unit. J Small Anim Pract Oct 1
  12. Hu S et al (2009) Observation on the effect of vitamin C in alleviating peroxidative damage in gut of dogs during enteral fluid resuscitation of severe burn shock. Zhonghua Shao Shang Za Zhi 25(6):451-453
  13. Lee JI et al (2006) Influence of ascorbic acid on BUN, creatinine, resistive index in canine renal ischemia-reperfusion injury. J Vet Sci 7(1):79-81
  14. Hastings D (2004) Suggested treatment for polyarthritis in dogs. J Am Vet Med Assoc 225(1):29
  15. Romano G et al (2008) Contrast agents and renal cell apoptosis. Eur Heart J 29(20):2569-2576
  16. Lee JI et al (2006) Attenuation of ischemia-reperfusion injury by ascorbic acid in the canine renal transplantation. J Vet Sci 7(4):375-379
  17. Hishiyama N et al (2006) Plasma concentration of vitamin C in dogs with a portosystemic shunt. Can J Vet Res 70(4):305-307
  18. Galler A et al (2012) Blood vitamin levels in dogs with chronic kidney disease. Vet J 192(2):226-231
  19. Winter JL et al (2009) Antioxidant status and biomarkers of oxidative stress in dogs with lymphoma. J Vet Intern Med 23(2):311-316
  20. Lopes-Santiago BV et al (2012) Evaluation of sperm DNA peroxidation in fertile and subfertile dogs. Reprod Domest Anim 47(6):208-209