Antioxidants are natural compounds found in many common fruits and vegetables. They can reduce free radicals and minimize the oxidative stress that contributes to canine cancer. Adding antioxidants to a dog’s diet is an easy way to provide nutritional support for cancer therapy.
- Antioxidants can help dogs.
- The strongest natural antioxidants include vitamin A, vitamin C, vitamin E, lipoic acid, uric acid, and carotene.
- Antioxidants may be helpful for your dog with cancer, but talk to your vet before starting an antioxidant supplement.
- The top five antioxidant foods for dogs are blueberries, blackberries, raspberries, strawberries, and broccoli.
What Are Antioxidants?
The term antioxidant is used to describe a wide range of chemicals that all act to neutralize free radicals in the body.
Free radicals are unstable molecules that can create havoc as they try to become stable. They are a normal part of life and are produced by your dog’s metabolism.2 They can also form as a result of injury or toxic exposure from the environment.2
High levels of free radicals can cause damage to cells and genetic material in the body. This effect is called oxidative stress and it is linked to many chronic diseases, including cancer.
Antioxidants are also called “free radical scavengers” because they neutralize free radicals.
Common antioxidants that you may recognize include:
- Vitamin A
- Vitamin C
- Vitamin E
- Lipoic acid
- Uric acid
- Coenzyme Q
Dark green leafy vegetables, yellow-orange fruits, and dark berries are often excellent sources of antioxidants. Fresh foods tend to contain higher levels of antioxidants because cooking and preservation for food storage can result in breakdown of these compounds.
You can also purchase antioxidant supplements as another way to introduce antioxidants into your dog’s diet.
The Benefits of Antioxidants
Antioxidants play a role in minimizing the effects of chemicals called free radicals in the body, which can help to prevent or treat cancer.
In vitro lab experiments have shown that the presence of antioxidants can cause a decrease in cancer development and increase in cancer cell death. But just because something can kill cancer cells in a laboratory setting doesn’t mean that it will work the same way in a living body.
Nine randomized, controlled clinical trials have been done in humans looking at antioxidants and cancer. These trials all focused on antioxidant supplements of various types rather than antioxidant-rich foods. Results over the nine trials were underwhelming, with most finding no impact from the antioxidants on people’s risk of developing cancer or the likelihood that they would survive it.2
A review of 174 studies that looked at antioxidants and chemotherapy had better news, however. This review found that antioxidants can be helpful to prevent negative side effects from chemotherapy, protecting normal cells from damage.3 Taking antioxidants during chemotherapy also seemed to help make the chemo more effective, and increased survival times in some cases.3
There is some concern that antioxidants could negate the effect of chemotherapy or radiation therapy. This is because part of how these treatments work is by creating free radicals within the cancer tissue to harm the cancer cells. Practitioners worry that giving antioxidants could protect the cancer cells as well as normal cells.
Although some studies have found this to be true,5,6 this only holds up for antioxidant supplements. Feeding your dog antioxidant-rich foods is unlikely to interfere with cancer treatments.5
If your dog is undergoing chemotherapy or radiation, discuss antioxidants with your oncologist. Feeding antioxidant-rich foods should be perfectly safe for most dogs, but your veterinarian may recommend avoiding antioxidant supplements.
Common Uses of Antioxidants for Dogs
Antioxidants are used in a number of ways. Some common uses for dogs include:6
- Part of treatment for many types of cancer and chronic disease.
- Minimize side effects from chemotherapy.
- Support the immune system.
Safety and Side Effects
Antioxidants can sometimes have negative effects.2
- High doses of potent antioxidants can bind to other dietary nutrients such as iron or zinc in the gastrointestinal tract and prevent them from being absorbed.
- Large doses of vitamin A can turn skin an orange color.
- Antioxidants have been shown in a small number of pre-clinical studies to increase tumor growth and metastasis through increase in circulating neoplastic cells.
- High doses of a single antioxidant can cause toxicity in some cases.
To avoid toxicity from individual antioxidants, using a pre-made supplement blend can help avoid accidental overdose.
When adding antioxidants through the use of fresh or cooked whole foods, add the new food item to your dog’s diet slowly to avoid stomach upset.
Using Antioxidants with Other Supplements and Treatments
Antioxidants, either as supplements or whole foods added to the diet, can be given with most medications but checking with a veterinarian prior to starting is recommended.
If your dog is undergoing chemotherapy or radiation, talk to your oncologist before giving an antioxidant supplement.
When to Not Use Antioxidants for Dogs
The effects of antioxidants on “oxidative stress” are relatively well known but the exact impact of antioxidants on chemotherapy and cancer treatment is less clear. There has been some concern for use of antioxidants with some specific chemotherapies that rely on oxidative stress and free radicals to kill cancer cells.
Overall, studies have shown that there is not a significant decrease in the effectiveness of chemotherapy when used with antioxidants.3 The use of antioxidants with chemotherapy may even minimize some of the side effects of chemotherapy, therefore increasing the patient’s quality of life.3
High levels of some specific antioxidant compounds can cause unwanted and potentially dangerous side effects. For example, vitamin E supplementation should not be taken with blood thinner medications.
How to Give Antioxidants to Dogs
Using whole foods will provide your dog with a variety of antioxidants, often in unknown or variable concentrations and amounts.2 Some foods that are safe for your dog to eat and contain antioxidants include:
- Cooked squash
- Sweet potatoes
- Red bell peppers
- Green beans
Antioxidants can also be purchased as individual supplements or in products that contain a combination of antioxidants. Supplements like colostrum contain several different antioxidants, including glutathione, vitamin E, vitamin C, and beta-carotene.8 Follow the dosing instructions for the particular product that you purchase for your dog.
The bioavailability of antioxidants can be affected by their preparation and processing. Many supplements are labeled for human use, so the appropriate dosing may be different for your pet. Consult your veterinarian for the appropriate therapeutic dose.
Most antioxidant supplementation is given daily for long term use.
What If I Miss a Dose?
If you miss a dose of an antioxidant supplement, just continue with the next scheduled dose as prescribed. Missing a dose is unlikely to have harmful effects.
Storage and Handling
Refer to the specifics for each supplement listed on their packaging.
Generally, most antioxidants should be kept tightly sealed and dry and away from heat and direct sunlight.
Store food items the same way you would if you were going to eat them.
Our Take on Antioxidants for Dogs
Antioxidants are relatively easy to incorporate into a dog’s cancer therapy without significant interactions or side effects from their current medications.
Dietary sources of antioxidants are an excellent choice and can easily be incorporated into your dog’s base diet or as an extra snack or topper. Remember, treats and toppers should be no more than 10% of your dog’s diet, to avoid unbalancing it.
If you are considering giving your dog an antioxidant supplement, discuss it with your oncologist and any other veterinarians involved in your dog’s care to ensure all parties are fully informed on which treatments are being administered.
- Halliwell, B. Antioxidants: The basics-what they are and how to evaluate them. Advances in Pharmacology. 1996; Vol 38: 3-20
- Antioxidants and cancer prevention. National Cancer Institute. https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/antioxidants-fact-sheet. Published February 6, 2017. Accessed November 29, 2022.
- Singh, K. Antioxidants as precision weapons in war against cancer chemotherapy induced toxicity – Exploring the armoury of obscurity. Saudi Pharmaceutical Journal. 2017; Vol 26: 177-190
- Nutrition service for cancer patients. Stanford Medicine Health Care. https://stanfordhealthcare.org/medical-clinics/cancer-nutrition-services/during-cancer-treatment.html. Accessed November 29, 2022.
- Dyer D, Clark C. Is it safe to take antioxidant supplements during chemotherapy and radiation therapy? Oncology Nutrition Dietary Practice Group. https://www.oncologynutrition.org/erfc/eating-well-when-unwell/antioxidant-supplements-safe-during-therapy#:~:text=There%20is%20no%20evidence%20to,about%20high%2Ddose%20antioxidant%20supplements. Published April 2013. Accessed April 22, 2023.
- Freeman, L. Antioxidants in Cancer Treatment: Helpful or Harmful? Compendium: Continuing Education for Veterinarians. April 2009: 154-158
- Higuera-Ciapara,I. Astaxanthin: A review of its chemistry and applications. Critical Reviews in Food Science and Nutrition. 2006. Vol 46: 185-196
- Asghar, Z. Antioxidant and radical scavenging activity of human colostrum, transitional and mature milk. Journal of Clinical Biochemistry & Nutrition. 2009. Vol 45: 150-154
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