The effect of vitamin C supplementation in healthy dogs on antioxidative capacity and immune parameters

Hesta, M., Ottermans, C., Krammer-Lukas, S., Zentek, J., Hellweg, P., Buyse, J., & Janssens, G. P. J. (2009). The effect of vitamin C supplementation in healthy dogs on antioxidative capacity and immune parameters. Journal of Animal Physiology and Animal Nutrition, 93(1), 26–34. https://doi.org/10.1111/j.1439-0396.2007.00774.x

Context for the Study

Vitamin C is a water-soluble antioxidant involved in numerous metabolic processes, including collagen synthesis, immune regulation, and oxidative stress protection. Unlike humans, dogs can synthesize their own vitamin C in the liver from glucose, reducing the need for dietary intake. However, research suggests that:

• Dogs produce lower amounts of vitamin C compared to some other species.
• Under stress or intense exercise, vitamin C production may not meet physiological demands.
• Vitamin C is thought to regenerate vitamin E, potentially enhancing antioxidant defense mechanisms.

These factors have led to interest in whether vitamin C supplementation provides additional health benefits in dogs, particularly for oxidative stress management and immune function.

Study Design

Researchers conducted a 36-day, 3-period crossover trial involving 15 healthy beagle dogs (7 males, 8 females, ranging from 8.6 to 18.4 kg in body weight).

• Each dog received one of three treatments daily: 0 mg, 30 mg, or 60 mg of vitamin C, combined with a constant 60 mg of vitamin E.
• Dogs were rotated through all three treatment groups in a controlled crossover design, ensuring each dog experienced all supplementation levels.
• Blood samples were analyzed for vitamin levels, oxidative stress markers, and immune parameters.

Key Findings:

• Plasma vitamin C levels slightly increased with supplementation, but the effect was not statistically significant.
• No measurable improvement in antioxidative capacity was found, as indicated by stable TBARS and uric acid levels.
• CD4+ lymphocyte counts increased in supplemented groups, but other immune parameters, including IgA and IgG concentrations, remained unchanged.
• No synergistic effect between vitamin C and vitamin E was observed, contradicting the hypothesis that vitamin C enhances vitamin E’s antioxidative function.
• A dose-dependent immune response was detected: 30 mg of vitamin C increased B-cell proliferation, while 60 mg appeared to have a suppressive effect.

Relevance to Canine Health

This study suggests that vitamin C supplementation may have minimal benefits in healthy, well-nourished dogs receiving sufficient vitamin E. However, its potential therapeutic role in dogs under oxidative stress, illness, or aging conditions remains an open question.