The A-B-C’s of Vitamin C

by Deborah E. Linder, DVM, MS, DACVIM (Nutrition)

Vitamin C is a nutrient we associate with helping the immune system and fighting off colds and keeping people healthy, but is this the same for dogs and cats? Let’s look at the A-B-C’s of vitamin C in pets.

Antioxidant?

Many people tout the benefits of vitamin C (also called ascorbic acid) as an active antioxidant. This is true. Sometimes. The motto “the dose makes the poison” is appropriate here. Antioxidants are meant to do what the name says: they combat oxidation in cells (another way to put it is that they prevent or delay some types of cell damage). While vitamin C does do this in smaller doses, in larger doses, it can be pro-oxidant, meaning it promotes the oxidation of cells and thus cell damage. Many pet owners reach for vitamin C, thinking it will help stave off cancer or prevent bladder stones or other diseases. Unfortunately, no studies have shown this to be the case in cats and dogs and sometimes can make things worse. Instead of potentially oversupplementing and causing harm, you should focus on providing healthy natural antioxidants through fruits and vegetables treats for your pet.

Body Requirement?

You may have heard of pirates and sailors getting scurvy – a disease of the connective tissues caused by a lack of vitamin C while out at sea without access to natural sources like the fruits and vegetables. Ever hear of a dog or cat getting scurvy? Likely not. Interestingly, this is one of the big differences between people and cats and dogs. While humans require vitamin C from the diet, the bodies of cats and dogs can make their own vitamin C, so you won’t see deficiency in our cats and dogs so even more reason not to supplement.

Calcium Oxalate?

Calcium oxalate stones can form in the bladder or kidney of dogs and cats. What does that have to do with vitamins? Like we mentioned above, cats and dogs don’t require vitamin C in the diet. Even more importantly, if it is supplemented above and beyond what their own bodies are making, we may be providing an excess of vitamin C. What happens to this excess? It gets metabolized and excreted from the body through the urine in the form of oxalate. Too much of this oxalate in the urine and your cat or dog may have an increased risk for calcium oxalate stones that can form anywhere in the urinary tract from kidneys to bladder. All the more reason to be cautious and talk with your veterinarian before giving supplements, which leads us to the last letter…

Don’t always assume that just because something is ‘natural,’ it will always have a benefit!

In the case of vitamin C, cats and dogs don’t have a dietary requirement and too much can not only have the opposite effect of your goal, but could come with some painful and unexpected side effects. Tell your veterinarian everything you are giving your pet and ask them before starting any new medication or supplement.

Deborah E. Linder, DVM, MS, DACVIM (Nutrition)

Dr. Deborah Linder, a board-certified veterinary nutritionist, is the head of the Tufts Obesity Clinic for Animals and has had articles appear in Eating Well, the Boston Globe, AARP, SHAPE, and XM Sirius Radio Doctor Channel. She has spoken at national and international conferences and a Capitol Hill briefing, and is an expert in pet obesity, nutrition communication, and in the human-animal bond. 

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