Vitamin C for dogs: Benefits and side effects

Vitamin C for dogs (like so many other dog vitamins!) is vital for health—but the good news is our best buddies make their own! Unlike people who depend on vitamin C-rich foods, our fur friends have an inner powerhouse that generates its own supply. This doesn't mean vitamin C for dogs isn't important (it is essential), but rather that healthy dogs don't require a supplement.

The benefits of vitamin C

Vitamin C is part of a group of nutrients called antioxidants, which are blessed with almost magical powers. They play an important role in preventing degenerative diseases, strengthening the immune system, combating aging, and reducing the risk of cancer. Examples of other essential antioxidants include vitamin E, carotenoids, and some trace elements. 

Antioxidants like vitamin C are much like a bomb disposal expert who prevents an explosive device from going off and doing terrible harm. In this case, the bomb is something called free radicals. They are present in the environment and have the potential to damage cells. 

In the biological world, free radicals are the bad guys. They are capable of destroying cells and creating cancers. Indeed, it is free radicals that create the cell damage linked to aging. Anything that cancels them out is equivalent to a superhero, which is exactly what vitamin C is.

And if you aren't yet sold on the importance of vitamin C, consider this: it forms part of a chain reaction that supplies energy (in the form of fat) to the mini-powerhouses (called mitochondria) inside each cell. Without vitamin C, the body would eventually grind to a halt—just like a car with an empty gas tank. 

How much vitamin C do dogs need?

By now you should have a pretty good understanding of the importance of vitamin C for dogs, and you want to be sure your dog is getting enough. Mother Nature has your back on this one because, unlike humans, a healthy dog has an internal factory (the liver) to make vitamin C on demand. 

In a single day, a dog makes about 18 mg of vitamin C for each pound of body weight. So a 60-lb Labrador makes around 1080 mg per day. And therein lies the rub: vitamin C needs to be delivered fresh every day. This is because vitamin C is a water-soluble vitamin that the body doesn't store in any quantity; it simply uses what it needs and pees the rest out. 

But this is just a guide to how much vitamin C to give (when needed.) Those dogs that require a supplement due to ill health, also have a higher requirement for this vitamin. Just like revving the engine on a race track burns through more fuel, a sick dog needs more vitamin C. 

Also, when dosing a sick dog, remember that the body can't store this vitamin. Instead of giving a single daily dose, split the total amount into three or four smaller amounts spaced out over the day. 

If you give too much vitamin C, the dog has a safety valve in that they pee out the excess. But some dogs have a lower tolerance than others, and a vitamin C supplement could result in a tummy upset or diarrhea. If this happens, cut back on the amount given and the diarrhea should settle. 

Side effects of low vitamin C

In people, low vitamin C leads to a condition known as  scurvy. Early explorers sailing the oceans commonly suffered scurvy due to a poor diet. They had symptoms such as bruising, bleeding gums, tooth loss, sore joints, and lack of energy. Untreated scurvy can be fatal. 

Vitamin C is no less important for dogs, but scurvy is rare in our canine companions because they don't depend on their food to supply this vitamin. A dog that is sick or has a higher than normal need for vitamin C could, in theory, become ill due to deficiency. But in reality, a dog that is so sick they don't make vitamin C shows signs of ill health that reflect their underlying disease. 

Do dogs need vitamin C supplements?

The short answer is no—healthy dogs do not need a vitamin C supplement. There are a small number of cases where extra vitamin C may be good, such as in dogs with severe liver disease. This is because it is one of the liver's many jobs to make the active form of vitamin C. When the liver doesn't work well, then the dog's vitamin C levels drop. 

The same can be argued for high performance dogs (such as those taking part in competitive sports such as agility or flyball) or endurance sledging dogs. Severe exercise causes more waste products to build up in the body, which then need to be detoxed and gotten rid of (those free radicals at work again!). Much like running a marathon, severe exertion places the body under stress, which in turn increases the dog's need for vitamin C as an antioxidant and to repair damaged cells. It could be argued that a supplement of vitamin C is good for these high performers.

As a parting thought, in human medicine, vitamin C plays at protecting the body from disease. An example of this is how some of you may take high doses of vitamin C at the first signs of a common cold. The idea here is that this vitamin makes the immune system better at fighting bugs and may stop you from getting sick. There is no scientific proof that this approach is helpful for our fur friends, especially as they make their own vitamin C. The jury is still out whether this is a good or bad thing for your dog… so when in doubt, have a chat with your vet.