You should seek the advice of your veterinarian if your pet is ill as only he or she can correctly advise on the diagnosis and recommend the treatment that is most appropriate for your pet.

Antioxidants (free radicals) are important for maintaining immunocompetence and some studies in cats suggest that dietary antioxidants may be beneficial in preventing age-related decline in immune response

There is an age-related decline in immune responsiveness to challenges from infection or vaccinations, and in humans a decline in plasma vitamin E concentration (below 1.35 mg/dl) has been associated with an increase in  incidence of infectious diseases in 66% of elderly patients over 60 years of age.(1)

Studies in dogs and cats conducted by the Waltham Centre for Pet Nutrition (2) have apparently confirmed that from age 6 years onwards total plasma antioxidant capacity in cats is significantly lower than in younger cats. Furthermore studies have been conducted looking at the effect of dietary antioxidants supplementation including :

• Vitamin E
• Vitamin C
• Taurine
• Carotenoids - B-carotene , lycopene

In one study (3) adult cats fed a ration supplemented with antioxidants were able to mount a significantly better immune response (as determined by mean circulating antibody concentrations) following vaccination with calicivirus vaccine than cats fed a control ration. In addition, erythrocytes in the cats fed antioxidant supplements were less fragile when subjected to osmotic haemolysis tests with salt.

In another study (4) vitamin E supplementation to both young and adult cats was demonstrated to 

• Increase serum vitamin E concentrations
• Significantly increase the stimulation of  lymphocyte proliferation in response to the mitogen concanavalin A in older cats - but NOT in the younger cats
• Decreased prostaglandin 2  production in both age groups.

Although further research is required it is likely that these findings have lead to the incorporation of antioxidants in dietary formulations for older animals, and animals with compromised immunity.

References

1. Chavance et al. Nutritional support improves antibody response to influenza virus vaccine in the elderly. British Medical Journal (1995) 291: 1348-1349

2.  Harper J. and Frith N Total plasma antioxidants in cats - normal range and influence of age (1999) The FASEB Journal 13 : 446.16

3.  Harper J. Feline Immunocompetence and the Role of Antioxidants. Proceedings North American Veterinary Conference 2001

4. Hayek MG et al. Dietary vitamin E improves immune function in cats. recent Advances in Canine and Feline Nutrition Vol III (2000) Iams Nutrition Symposium.

Updated January 2016