There is a lot of conflicting information online whether or not to feed Vitamin C, and although there are Vitamin C supplements on the market, they aren't necessary for most dogs. Vitamin C is synthesized in the dog’s liver and they do not require an external source. You may have the urge to feed Vitamin C because of its antioxidant properties and because it is an essential Vitamin for humans to include in their diet. And while you may be tempted to share an orange slice with your dog, I urge you to reconsider! They are high in sugars and can even cause GI upset if fed too much.
Vitamin C is produced in the dog’s liver. Humans cannot produce their own Vitamin C, therefore it must be included in a human diet. Vitamin C is an antioxidant, which is important because antioxidants remove harmful free radicals from the body. Free radicals are unstable molecules produced as a byproduct of oxidation. They can cause damage to genes, which speed up the aging process and can play a role in development of cancer and other diseases and illness in the body.
Because dogs produce their own Vitamin C, they are already creating their own antioxidants. There are other antioxidants, however, that dog’s should be getting from their diet,including Vitamin E and Selenium.
Vitamin E and Selenium is best found in grass fed beef. Selenium is concentrated in beef liver. If you are feeding a diet that meets the daily requirements of both Vitamin E and selenium, you should not have to supplement an antioxidant.
Supplements for dogs have become increasingly popular, because kibble is lacking in natural essential vitamins and minerals. Low-quality proteins (factory farmed proteins), and/or the high-heat process in manufacturing kibble requires these companies to use synthetic vitamins and minerals in their product. The problem with this is that synthetic vitamins are not absorbed as well as natural vitamins. Pet food companies have taken advantage of this and have used this to market an array of supplements that are not actually needed, unless your dog has a deficiency.
There are some cases in older dogs or dogs with illness that may be deficient in certain vitamins or minerals that require supplementation. Vitamin C deficiency is rare, and has been seen in Hypertrophic Osteodystrophy (HOD) which happens to young, fast-growing large/giant breed puppies (like Great Danes). Adult dogs are unlikely to experience a Vitamin D deficiency.
The best way to determine if your dog is deficient in any vitamins in minerals is to take them at least annually to the vet for a blood panel.
If you are feeding a fresh food diet with a lot of variety, it should provide your dog with all of the necessary vitamins and minerals. For example, Vitamin D is found in fish, beef and eggs. Vitamin C is naturally found in leafy greens and cruciferous vegetables. To help your dog digest and get the most from veggies, they should always be steamed or pureed before feeding. As always, you should feed the dog in front of you. Supplementing isn’t necessary if you are feeding a variety of whole food. But If you are interested in adding extra to your dog's bowl, other sources of Vitamin C include broccoli, spinach, kale- or fruits like blueberries or currants. What works for one dog, may not work for another.