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Why Adding Vitamin C to Your Dog's Diet is not always a Wise Thing to Do…

From the desk of Mogens Eliasen - first published: October 21, 2006 (revision of an previous article from 2003)

Mogens Eliasen - the author of this article
on 'vitamin C'

Research has shown that, for dogs as well as for people, a large overdose of Vitamin C can significantly boost the immune system and help the body to a fast healing of many injuries. For people, it has even been shown that a constant large overdose of some 5,000 -10,000 mg/day can prevent about 90% of all the major diseases that kill people.

From there, it might make sense to conclude that extra Vitamin C is good for people. But it does not make sense to make the same conclusion for dogs…

The dog's internal production of Vitamin C (Ascorbic Acid)

In their bodies, dogs produce about 40 milligrams of this vitamin per kilogram bodyweight every day - or 18 milligrams per pound, if it is an American dog. A 40-pound dog thus produces the equivalent of about two big tablets (500 milligrams) per day! A dog the size of a human would produce about 6-8 of those big 500-mg tablets per day - a huge dose, even compared to what a human needs!

An important thing to notice here is that this production leads to a constant concentration of Ascorbic Acid in the blood. This means that all cells and organs in the dog's body are used to (and also depend on) this steady supply in small concentrations that never fluctuate very much.

Some fundamental body chemistry

In order to understand this, you need to understand some fundamentals of chemistry. Let consider two chemicals, A and B, who react with each other to produce the products C and D. Chemists like to visualize this in the following way:

A + B -> C + D

But most chemical reactions can actually be reversed also. If we add some D to C, those two will react and generate some A and B:

C + D -> A + B

This is what happens whenever we have a chemical equilibrium. And most processes in the body are subject to this. They are fine-tuned equilibriums that can run either way, subject to which chemicals are abundant and which one are under-represented. This is illustrated by making the arrow point both ways, indicating that the reaction can run either way, subject to circumstances:

A + B <-> C + D

What tangibly goes on at the molecular level is this: every time a molecule of A meets a molecule of B, they may combine and produce C and D - or depart again as A and B. Same thing with C and D. When two representatives of them meet, they may react with each other and re-generate A and B. But they could also remain C and D. It depends on the nature of the species, A, B, C, and D.

We have equilibrium when we cannot measure any changes of the total concentrations of any of the four chemicals. That equilibrium is maintained through a constant chemical activity through the two reactions that exactly oppose each other.

Each equilibrium can be quantitatively expressed in a way that is equivalent to measuring gravity (and equally fundamental!), taking into account that, in chemistry, energy is related to concentration, not mass:

= Constant that is specific for this equilibrium.

Putting brackets around a chemical species is the traditional way for chemists to express the concentration of that species.

When we have achieved equilibrium, we can watch what happens when we add more of A to the mixture of the four: This will greatly increase the chances of a B molecule meeting an A molecule, so we will have a greater likelihood of B molecules reacting with A molecules. The result of this will be that our addition of A will consume a big chunk of what was left of B - and produce more of C and D!

You can see it from the math also: If you increase [A] and Nature insists that the Constant remains constant, then something must happen that will reduce the now too high value of the fraction! An increase of either [C] or [D] or both is the only possibility that exists. This means that the chemistry must now runs in a direction that will generate some of those. At the same token, you see that we also get a reduction of [B]….

But if we instead add a large amount of C, then the process will "run the other way", and the excess amount of C will react with a big portion of D to generate more of both A and B.

So, in essence, when we add C, the result in the body is a reduction of D!

Did someone say "Oops"?

Some fundamental physiology…

Nature has a fundamental rule that says, "Use it - or lose it". This rule most definitely applies to any organs ability to provide an outcome of some kind, such as a production of work, whether the output is energy or internal chemicals. All athletes know this rule: if they do not keep their muscles working, they lose their strength. Anyone who has had a broken limb in a cast can testify to the speed at which this happens.

It is also well-known in medicine. If you artificially add to the body any chemical it is supposed to produce itself, the body will shut down that internal production and instead make itself dependant on the external supply! Using injections of hormones and steroids that are also produced by the body itself, is a very dubious, if not outright dangerous affair, no matter how beneficial it can be in the short term. Using Cortisone to fight inflammation is one such example - it can shut down the entire production of the adrenal glands if extended for months… And the adrenal glands produce more than just Cortisone.

This could very well be connected to the reason why humans depend on external supply of vitamin C, whereas dogs don't. Humans, as descendants from fruit-eating monkeys, had more than enough external supply from the food, so our bodies do not need to produce vitamin themselves - until we stop eating fruits and fresh vegetables in the amounts we should…

The problems with supplementing…

Some more bad news is that we do not know in detail all the specific chemical reactions in the dog's body that produce Ascorbic Acid, which could be chemical C in our example above. We also do not know what other chemicals are generated along with Ascorbic Acid in the process - the D's are unknown. Some of them could be very important for the dog's metabolism, though - we don't know!

But we do know that, whatever those D's are, they will cease to be produced when we add significant amounts of Vitamin C to our dog's diet! And we do know that when we constantly supply Vitamin C to a dog, it will shut down its own ability to generate this vitamin, maybe permanently.

Another thing that we do know is that the dog's liver and kidneys do not like dealing with sudden and very high concentrations of Ascorbic Acid. They instantly start processes to rid the body of this excess poison, and it does not take many minutes before the kidneys' work can be measured in the urine! In a couple of hours, those internal organs have the situation "back to normal" with all the excess either destroyed in the liver or discharged through the kidneys - which stresses these organs to work much harder than they are designed to.

Scientific research also shows that the result of a long-term supply of excess vitamin C for dogs can lead to kidney and liver damage that sometimes can be fatal… This really should not surprise anyone who understands the chemistry involved.

Getting the perspective right

Now, 40 mg/kg/day (or 18 milligrams/day per pound body weight) is quite a lot... You cannot feed a dog enough fresh fruits to ever reach more than about few percent of that! So, feeding fresh fruit will not cause a shutdown of the body's internal productions. And it cannot cause the liver or kidneys to become overworked. In fact, such a supply will simply cause only a small disturbance in the body equilibrium, which simply will shift towards a slight reduction of its own production, so the net result will be that the blood's concentration of Ascorbic Acid remains the same. It is similar to what happens when you add a small amount of acid to a pH-buffered solution.

However, there are many people who have seen great effects of using Vitamin C supplementation in large doses to deal with a specific problem, like an infection or injury, and they then conclude that it is great to continue doing it....

On a temporary basis, supplementing can be acceptable and reasonable. Supplementation then functions the same way as medication does: it helps the body fight a temporary problem - at the risk of unpleasant side-effects and at the certain expense of long-term damage, if continued.

The chemical laws involved in this are as fundamental as gravity - there are NO EXCEPTIONS! The danger, of cause, is that you may not see the effects of the shutdown immediately - in fact, you might not see it until many months or years later, and then you will have no clue about connecting the problem to your supplementing an unnecessary ingredient.

This also means that a life-long supplementation of vitamin C to certain breeds should be completely out of the question: if dogs truly need that, they should not be bred!

The bottom line is that you should NOT add vitamin C to a dog's diet at all, unless you have a very specific acute target (infection, injury) as the reason. In those cases, please help your dog fight the infections faster by giving it some huge amounts of Vitamin C over the few days it takes to get well - and then stop the supplementing again! Use it as you would take antibiotics for yourself.


Mogens Eliasen


Mogens Eliasen holds a mag. scient. degree (comparable to a US Ph. D.) in Chemistry from Århus University, Denmark, has a extensive education also as military officer and in business management. He has been working with dogs, dog owners, dog trainers, and veterinarians since 1970. A large part of his dog work has been in the area of education and education planning, and as consultant for dog owners and dog training associations. He is a strong advocate of treating the dog with respect for its nature as domesticated wolf, and has published several books and videos on topics related to dogs, dog training, dog behavior, and responsible care of dogs. He publishes a newsletter "The Peeing Post" containing lots of tips and advice on all matters pertaining to dogs.

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Titles available from K9joy®:

Anders Hallgren:
"The ABC's of Dog Language" (140 page book - 1996)
Understand what your dog is telling you - and communicate with it on its own terms. A must have for all dog lovers. Easy to read. Easy to use as reference.

Mogens Eliasen:
"The Dog's Social Behavior" (2.5 hr. video - 1998, updated on DVD 2006, with support materials on a CD)
How the dog's behavior is linked to its instincts and needs. What you can change and what is "for life". How you use this information to dramatically improve your relationship with your dog.

Mogens Eliasen:
"BrainWork for Smart Dogs" (380 page e-book - 2003)
How you get a happy and well-behaved dog, stimulating its brain with 15 minutes of fun per day. Dogs need to work and use their instinct in order to be in mental balance. Everyone can do it with these instructions. More than 40 exercises to choose from!

Mogens Eliasen:
"Don't Pull on the Leash!" (40 page e-book - 2005)
The 5 simple steps in this complete training manual will effectively stop any dog from pulling on the leash, with no pain or abuse and no special equipment - and make the start of a much better relationship with the dog.

Mogens Eliasen:
"Is Your Dog's Drinking Water Safe?" (30 page e-book - 2005, updated 2006)
A layman's overview of how and why drinking water gets contaminated - and what you can do about it.

Mogens Eliasen:
"Feeding Your Dog - the Natural Way" (1 hr. video - 1998)
The fastest introduction to get you started on feeding your dog a natural diet. It explains the dog's physiology in simple terms, so you also understand why you should do this.

Mogens Eliasen:
"Canine Choice - by Nature" (80 page e-book - 1999, updated 2005)
The simple "how-to" about feeding a natural diet for optimal health.

Mogens Eliasen:
"Raw Food for Dogs - the Ultimate Reference for Dog Owners"
(340 page e-book - revised/expanded 2006)
Everything you need for making your own informed decisions about what to feed your dog, and why and how. Includes numerous examples of feeding plans plus two chapters on how to work with your vet, also if he/she does not approve of your feeding...

Mogens Eliasen:
"The Wolf's Natural Diet - a Feeding Guide for Your Dog?"
(125 page e-book - 2004 updated/revised 2006)
What we know and don't know about the wolf and its natural feeding, and about the dog and its domestication, and what we can and cannot conclude from wolf to dog... this is the big "why?" behind any responsible approach to feeding your dog.

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