Pet owners increasingly look for health and wellness benefits from pet foods beyond basic nutrition. While dog foods may make claims about their benefits on pets’ immune systems, research into how functional ingredients affect dogs’ immune function remains limited. Researchers at the University of Porto, Portugal reviewed 27 published scientific studies looking into how vitamins, minerals and phytonutrients affect dogs’ ability to fight off infection.
“Although vitamin supplementation is often claimed to support immune function, only two studies promoting slight benefits of vitamins C and E were found,” the scientists wrote in the journal Veterinary Sciences. “The limited research on minerals suggests that organic sources promote a better immune response. Studies evaluating the inclusion of different phytonutrients show that these compounds might exert immunomodulatory and anti-inflammatory effects.”
Although functional ingredients may support dogs’ immune systems, the scientists pointed out several issues with making definitive claims. For one, there aren’t many studies on the subject. What’s more, many of the studies they reviewed were conducted with healthy young adult dogs. However, dogs’ immune systems change throughout their lives.
“Studies in senior dogs indicate an impairment of cell-mediated immunity, with reduced blood CD4 T-cells and a lower response of blood lymphocytes to stimulation by mitogens,” the researchers wrote. “Conversely, puppies are at risk of developing infectious diseases as their immune system is still undergoing maturation. While studies conducted in puppies and aged dogs suggest an improvement of immune status with dietary supplementation of different functional additives (organic selenium, curcumin, gallic and gallnut tannic acids and β-carotene), there is a significant lack of evidence regarding the potential influence of these compounds in the immune system of these dogs.”
Another shortcoming of existing research is that they often only lasted for a short period, meaning the long-term effects are largely unknown. Also, pet dogs range widely from Chihuahuas to Great Danes, whereas many studies are conducted on a single breed or otherwise genetically similar groups of dogs.
Vitamins, minerals and phytonutrients influence on dogs’ immune systems
In their meta-analysis, the authors noted that vitamins play a key role in immune regulation. Fat-soluble vitamins (A, D, E, K) and water-soluble ones (B-complex, C) contribute to various physiological functions. Vitamin C, synthesized in dogs’ livers, and vitamin E, with potent antioxidant properties, protect immune cells from oxidative stress. These vitamins also support T-cell function and regulate inflammatory mediators. Existing studies suggested that at least two vitamins had observable effects on dogs’ immune responses.
- Vitamin E and Inflammation: High-dose vitamin E supplementation reduced inflammatory markers in osteoarthritic dogs, improving joint health.
- Vitamin E and C Synergy: A combined low-dose supplementation increased CD4+ cell counts and enhanced lymphocyte activity, but excessive vitamin C showed inhibitory effects.
Macro and trace minerals sustain physiological and metabolic processes, including immunity. Research highlights their bioavailability and immune modulation potential.
- Zinc: Organic zinc supplementation improved T cell differentiation (CD4+) compared to inorganic sources. Enhanced bioavailability may make organic forms preferable.
- Selenium: Organic selenium sources like selenohomolanthionine improved vaccine antibody responses and cytokine production. Selenium chelates further modulated immune-related gene expression.
- Calcium Fructoborate (CFB): A source of boron, CFB reduced inflammatory markers in osteoarthritic dogs and improved mobility.
- Chromium Propionate: Supplementation increased inflammatory and immunoglobulin markers but requires more robust studies to confirm benefits.
Phytonutrients such as carotenoids and polyphenols demonstrate anti-inflammatory and antioxidant properties. Studies found evidence of this.
- Carotenoids: Lutein and β-carotene enhanced both cellular and humoral immunity, with β-carotene showing benefits for aging dogs by improving T cell responses. Astaxanthin improved NK cell activity and reduced oxidative damage.
- Polyphenols: Green tea polyphenols and curcumin reduced pro-inflammatory cytokines and supported gut health in dogs with obesity and musculoskeletal issues.
- Other Phytonutrients: Grape seed proanthocyanidins reduced inflammatory markers in dogs with inflammatory bowel disease (IBD). Gallic acid and tannins alleviated stress-induced inflammation and gut dysbiosis.