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Vitamin C in Veterinary Medicine

Nov 16, 2023

Vitamin C is the common name for a chemical called “ascorbic acid”. This is an essential nutrient for humans, and as such is regularly supplemented if dietary intake is not sufficient. However, this does not hold true for the majority of animals. In all species other than primates and guinea pigs, Vitamin C is produced by the liver through the action of an enzyme called “gulonolactone oxidase”. As such, in the majority of veterinary species, Vitamin C is not an essential nutrient as it is produced by the body in the amount required for life. It is a water-soluble vitamin, which means that it dissolves in water and does not have a storage form in the body. It is produced or taken in as required and there are no significant reserves to draw from.

There are multiple roles played by Vitamin C in the body. Among the most crucial is the production of collagen. Collagen is a primary constituent of bone, teeth, and connective tissue fibers, and is produced during skeletal growth and development. Vitamin C is also essential for the repair of damaged tissues. As such, humans and guinea pigs fed inadequate vitamin C may develop “scurvy”, a condition characterized by inadequate collagen resulting in loosening teeth, bleeding, and other issues. This condition is not recognized in dogs and cats, as they are unable to develop a deficiency due to their capacity to produce their own Vitamin C.

Aside from the effects of Vitamin C as a substrate for collagen synthesis, it also has roles as an antioxidant due to its ability to neutralize oxygen derived free radicals. It also has effects on immune function. It may also acidify the urine, which may be helpful or harmful in several situations.

While it is well known that a deficiency of Vitamin C causes many issues, there is debate as to whether or not an increased or “supranormal” amount is beneficial.

Research in human medicine has investigated the role of Vitamin C in several conditions, including cancer, severe sepsis, and other life-threatening diseases; as well as to prevent or treat more minor conditions such as the common cold. At this point, results have been generally disappointing. There is some evidence to suggest that its supplementation may reduce the duration of the common cold, but little other evidence. Recent research in human medicine (see the “CITRIS ALI” trial) have suggested minimal to no effect in critical illness, and the utility of mega-dosing for the treatment of cancer has not been demonstrated.

Vitamin C may be utilized by veterinarians in some specific situations- for example in the treatment of certain toxins, where antioxidant effect or urinary acidification may be beneficial.

Despite the lack of a dietary requirement, Vitamin C may occasionally be included in pet food because of its ability to act as an antioxidant, preventing spoiling and rancidity. Its effectiveness as an antioxidant is limited unless it is combined with other antioxidants such as vitamin E. Vitamin C is also poorly stable at room temperature, and as such supplements generally need to be refrigerated. After several months, most vitamin C in foods or supplements becomes inactive unless chilled.

There is, in general, no accepted benefit to vitamin C supplementation in veterinary medicine. It is however unlikely that physiologic doses will cause any adverse effects. Very large (“megadose”) Vitamin C supplementation also tends to be well tolerated, though there is a possibility of adverse effects such as urinary acidification, which may promote the formation of certain bladder stones; GI upset; or other minor intolerances. As such, discuss with your veterinarian the possible risks and benefits of any supplement prior to starting therapy, especially if other conditions are present.

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