In a healthy body, free radicals and antioxidants are in balance.

Free radicals are unstable molecules containing oxygen and an odd number of electrons. They “steal” electrons in a process known as oxidation, which is a normal process in the body.
Antioxidants can stabilise free radicals by donating electrons without impairing their own stability. This neutralises the free radicals and reduces capacity for damage.
“Redox state” is the balance between the levels of oxidants (substances that cause oxidation) and antioxidants (substances that inhibit oxidation). In biological contexts, particularly in cells and tissues, maintaining a balanced redox state is crucial for proper functioning and health.
Oxidative stress occurs when antioxidants fail to keep the free radicals in check, leading to an imbalance between the free radicals and the antioxidants. Oxidative stress can cause damage to cells, proteins, lipids and DNA. Oxidative stress also occurs in dogs. Antioxidant-rich foods can help to reduce oxidative stress.

The effect of diet

Blueberries and other fruit containing phenolics that react with free radicals are good antioxidants: one study which compared antioxidant levels in sled dogs fed blueberries found that the dogs who were given blueberries were better protected against oxidative damage than those fed the control diet in the study[1]. In other words, supplementing the diet with blueberries to maintain antioxidant levels can help to provide exercise-induced damage in dogs.

Studies on the effects of the diet on redox state in particular relation to dogs are more difficult to find[2]. However, there is research to indicate that antioxidants have beneficial effects, not least on age-related cognitive and behavioural changes[3]. For example, one study looked into potential links between levels of trace elements and antioxidants in dogs with behaviour problems such as destructiveness, aggression, fearfulness and excessive activity. It found that improving zinc and antioxidant status with food supplements might aid in preventing and resolving behavioural problems in dogs[4].

Another study[5] into the effect of dry food on the oxidative profile of dogs noted that the inclusion of adequate concentrations of antioxidants is recommended to counterbalance free radicals and reactive oxygen species (ROS). In other words, including antioxidants in dog diets can reduce vulnerability to oxidative stress. It also found that the specific formulation and quality of dry dog food can affect its effectiveness in mitigating oxidative stress and that genetic factors and overall health also play a role in oxidative stress responses. And probably what we already knew: food consumption and preference will affect overall antioxidant intake.

Other studies found that older dogs fed food enriched with a broad-spectrum of antioxidants learned significantly more quickly than older dogs fed on a controlled diet, and indicated not only that age can affect performance but that administering food enriched with supplemental antioxidants, even in the short term ,can partially reverse the effects of ageing on cognition[6]. A similar study that examined the benefits of a “broad-spectrum” antioxidant diet suggested that long-term dietary intervention can “buffer” age associated cognitive decline[7].

Not all antioxidants are equal

There are various types of antioxidants, including vitamins (such as vitamin C and E), minerals (like selenium and zinc), flavonoids, polyphenols, and carotenoids (such as beta-carotene). Each type may have different roles and mechanisms of action in the body.

In terms of bioavailability, some antioxidants are more readily absorbed and used by the body than others. For example, certain antioxidants found in fruits and vegetables may be more bioavailable than those in supplements. Plant extracts are extremely effective antioxidants, most commonly due to phenolic acids, phenolic diterpenes, flavonoids (including quercetin and kaempferol), and volatile oils (e.g., thymol, and menthol).

The combined effect of multiple antioxidants may be greater than the sum of their individual parts because antioxidants often work together synergistically in the body. So a diet rich in a variety of antioxidant-containing foods is likely to provide better protection against oxidative stress than relying on a single antioxidant supplement. And different antioxidants may also have specific roles in the body: for instance, vitamin E is known for its role in protecting cell membranes from oxidative damage, while flavonoids may have anti-inflammatory effects.

Antioxidant-rich foods

For dogs, antioxidants are best obtained from safe and suitable foods.

As a rule of thumb, the presence of pigments often correlates with antioxidant content, but antioxidant capacity isn’t determined only by colour. Even factors like ripeness and storage could affect antioxidant levels. A varied diet including a spectrum of colourful fruits and veg is the best way of ensuring broad range of antioxidant intake:

  • Red and purple fruits like berries often contain anthocyanins, which are known to fight oxidative stress.
  • Orange and yellow foods like carrots and sweet potatoes are rich in beta-carotene and other carotenoids which not only gives them their bright colours but also help to protect cells from damage.
  • Leafy green vegetables like spinach and kale (and broccoli) contain chlorophyll as well as lutein and zeaxanthin, which are known to promote eye health.

Antioxidants are also present in almonds and flaxseeds, but they must be kept as a very occasional treat because of their high-fat content. Other less obvious sources that are also suitable for dogs include green tea and spices like turmeric and ginger.

Finally, antioxidants aren’t a silver bullet. The results of yet another study suggested that their effectiveness in reducing age-dependent decline is also dependent on environmental and behavioural enrichment[9].

Some studies have suggested that exercise can play a part in oxidative stress.

Dogs’ performance is also influenced by training, activity and daily play…

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References:

[1] Dunlap KL, Reynolds AJ, Duffy LK. Total antioxidant power in sled dogs supplemented with blueberries and the comparison of blood parameters associated with exercise. Comp Biochem Physiol A Mol Integr Physiol. 2006 Apr;143(4):429-34. doi: 10.1016/j.cbpa.2005.09.007. Epub 2006 Mar 6. PMID: 16520073.
[2] Gabriel F E Pacheco, Rafael C Bortolin, Paloma R Chaves, José C F Moreira, Alexandre M Kessler, Luciano Trevizan, Effects of the consumption of polyunsaturated fatty acids on the oxidative status of adult dogs, Journal of Animal Science, Volume 96, Issue 11, November 2018, Pages 4590–4598, https://doi.org/10.1093/jas/sky313
[3] Zicker SC. Cognitive and behavioral assessment in dogs and pet food market applications. Prog Neuropsychopharmacol Biol Psychiatry. 2005 Mar;29(3):455-9. doi: 10.1016/j.pnpbp.2004.12.010. PMID: 15795054.
[4] Alaleh Soltanian, Javad Khoshnegah, Mohammad Heidarpour, Comparison of serum trace elements and antioxidant levels in terrier dogs with or without behavior problems, Applied Animal Behaviour Science, Volume 180, 2016, Pages 87-92, ISSN 0168-1591, https://doi.org/10.1016/j.applanim.2016.04.012.
[5] Usuga A, Rojano BA, Duque JC, Mesa C, Restrepo O, Gomez LM, Restrepo G. Dry food affects the oxidative/antioxidant profile of dogs. Vet Med Sci. 2023 Mar;9(2):687-697. doi: 10.1002/vms3.1064. Epub 2023 Jan 12. PMID: 36634249; PMCID: PMC10029885.
[6] Milgram NW, Head E, Muggenburg B, Holowachuk D, Murphey H, Estrada J, Ikeda-Douglas CJ, Zicker SC, Cotman CW. Landmark discrimination learning in the dog: effects of age, an antioxidant fortified food, and cognitive strategy. Neurosci Biobehav Rev. 2002 Oct;26(6):679-95. doi: 10.1016/s0149-7634(02)00039-8. PMID: 12479842.
[7] Nippak PM, Mendelson J, Muggenburg B, Milgram NW. Enhanced spatial ability in aged dogs following dietary and behavioural enrichment. Neurobiol Learn Mem. 2007 May;87(4):610-23. doi: 10.1016/j.nlm.2007.01.001. Epub 2007 Feb 15. PMID: 17303448.
[9] Milgram NW, Head E, Zicker SC, Ikeda-Douglas C, Murphey H, Muggenberg BA, Siwak CT, Tapp PD, Lowry SR, Cotman CW. Long-term treatment with antioxidants and a program of behavioral enrichment reduces age-dependent impairment in discrimination and reversal learning in beagle dogs. Exp Gerontol. 2004 May;39(5):753-65. doi: 10.1016/j.exger.2004.01.007. PMID: 15130670.

Want to know more? These studies might be useful:

Lobo V, Patil A, Phatak A, Chandra N. Free radicals, antioxidants and functional foods: Impact on human health. Pharmacogn Rev. 2010 Jul;4(8):118-26. doi: 10.4103/0973-7847.70902. PMID: 22228951; PMCID: PMC3249911.(Although the title refers to human health, this paper also includes information relating to animals.)
Petcu CD, Mihai OD, Tăpăloagă D, Gheorghe-Irimia RA, Pogurschi EN, Militaru M, Borda C, Ghimpețeanu OM. Effects of Plant-Based Antioxidants in Animal Diets and Meat Products: A Review. Foods. 2023 Mar 21;12(6):1334. doi: 10.3390/foods12061334. PMID: 36981260; PMCID: PMC10047951.
Manessis, G.; Kalogianni, A.I.; Lazou, T.; Moschovas, M.; Bossis, I.; Gelasakis, A.I. Plant-Derived Natural Antioxidants in Meat and Meat Products. Antioxidants 2020, 9, 1215. https://doi.org/10.3390/antiox9121215
Cotman CW, Head E, Muggenburg BA, Zicker S, Milgram NW. Brain aging in the canine: a diet enriched in antioxidants reduces cognitive dysfunction. Neurobiol Aging. 2002 Sep-Oct;23(5):809-18. doi: 10.1016/s0197-4580(02)00073-8. PMID: 12392784.
Milgram NW, Zicker SC, Head E, Muggenburg BA, Murphey H, Ikeda-Douglas CJ, Cotman CW. Dietary enrichment counteracts age-associated cognitive dysfunction in canines. Neurobiol Aging. 2002 Sep-Oct;23(5):737-45. doi: 10.1016/s0197-4580(02)00020-9. PMID: 12392778.
M.S. Brewer. Natural Antioxidants: Sources, Compounds, Mechanisms of Action, and Potential Applications https://doi.org/10.1111/j.1541-4337.2011.00156.x

Important Considerations:

  • Always consult your veterinarian before making any significant dietary changes, particularly where there are pre-existing health conditions or dietary restrictions.
  • If you plan to use an ingredient, check the label to see whether it’s in your dog’s food before giving more. Excessive intake of any foods can have adverse effects.
  • Ensure (where possible) that you use high-quality, organic products specifically formulated for pets (or better still, human grade ingredients) to avoid any potential adverse effects.
  • Introduce new foods gradually to avoid adverse effects such as gastrointestinal upset or diarrhoea.
  • I provide nutritional information purely as a helpful guide. Nutritional information on ingredients is obtained from the US Department of Agriculture’s FoodData Central site (https://fdc.nal.usda.gov/index.html) and any nutritional information provided in recipes is based on an online calculator: calories and other information will vary based on brands, ingredients and other factors.
  • Check nutrient levels and recommendations for your dog’s weight, age and activity. For example this nutritional guideline produced by FEDIAF.