Dave Zanoni
When we see vitamins listed on a pet food or supplement, it is easy to think one thing: more must be better.
Vitamin A, vitamin D, vitamin E, B vitamins, vitamin C. They all sound healthy, and they are important.
But one of the most important lessons in nutrition is also one of the simplest:
An essential nutrient is not automatically better just because we provide more of it.
Dogs and cats need vitamins for vision, growth, reproduction, metabolism, nervous system function, blood clotting, tissue maintenance and many other processes. The goal, however, is not to put the largest possible amount of nutrients into the bowl.
The goal is balance.
Not All Vitamins Behave the Same Way
Vitamins are generally divided into two groups.
Fat-soluble vitamins include vitamins A, D, E and K. They are absorbed along with dietary fat, and several can be stored within the body.
Water-soluble vitamins include vitamin C and the B-complex vitamins. These are handled differently by the body, and excess amounts are generally not stored to the same extent as fat-soluble vitamins.
This distinction matters because vitamins that can be stored have a greater potential to accumulate when excessive amounts are consumed over time.
That is why nutrition is not simply about preventing deficiency. We also have to understand excess.
Vitamin A: A Perfect Example of Why Dogs and Cats Are Different
Vitamin A is involved in vision, growth, reproduction and the maintenance of healthy epithelial tissues. Those tissues include the skin and the protective linings of areas such as the respiratory and gastrointestinal tracts.
But vitamin A also shows us something fascinating about the nutritional differences between dogs and cats.
Plants contain carotenoids such as beta-carotene. Dogs are capable of converting certain carotenoids into active vitamin A.
Cats cannot rely on that conversion to meet their vitamin A requirement.
Cats therefore require a dietary source of preformed vitamin A.
This is one of many reasons I tell people that a cat is not simply a small dog. The two species have important metabolic differences, and those differences affect how we should think about their nutrition.
Vitamin A also demonstrates why more is not always better.
Deficiency can interfere with growth, reproduction and normal epithelial integrity. On the other side of the equation, excessive vitamin A can contribute to skeletal abnormalities.
Essential does not mean unlimited.
Vitamin D: More Than a Bone Vitamin
Most people associate vitamin D with bones, but its role is much broader.
Vitamin D is deeply involved in the regulation of calcium and phosphorus within the body. It helps support calcium and phosphorus absorption from the intestinal tract and participates in maintaining appropriate concentrations of these minerals.
The liver and kidneys are also involved in converting vitamin D into biologically active forms.
This is a good example of how nutrients work together rather than independently.
Vitamin D, calcium and phosphorus are interconnected.
Too little vitamin D can interfere with normal bone mineralization. Too much can also create serious problems.
Excess vitamin D can cause hypercalcemia, or abnormally high calcium in the blood, along with bone resorption and mineralization of soft tissues.
Once again, the goal is not more.
The goal is the appropriate amount within the total diet.
Vitamin E: Protecting Cells From Oxidative Damage
Vitamin E performs an important antioxidant function.
The polyunsaturated fatty acids found in foods and in the body's cell membranes are particularly vulnerable to oxidation. Vitamin E helps protect those fats from oxidative damage.
This is another reason we cannot evaluate nutrients in isolation.
The amount and type of fat in a diet can influence the importance of adequate antioxidant protection.
Nutrition is a system.
Changing one part of that system can influence another.
That is why looking at a single ingredient or nutrient rarely tells us everything we need to know about a food.
Vitamin K and Normal Blood Clotting
Vitamin K may not receive as much attention as vitamins A, D and E, but its primary role is extremely important.
Vitamin K is required for the body's normal blood-clotting mechanisms and is involved in the production of several clotting factors.
There is another interesting part of the story.
Bacteria living within the intestinal tract can synthesize vitamin K, and this bacterial production can contribute to a dog's or cat's vitamin K supply.
That contribution can become less reliable when intestinal bacterial populations are reduced, including during treatment with certain antibiotics.
Vitamin K metabolism is also why certain anticoagulant rodenticides are so dangerous. These poisons interfere with vitamin K activity and can prevent normal blood clotting.
The lesson here is bigger than vitamin K itself. The digestive tract, intestinal bacteria, nutrients and metabolism are all interconnected.
The B Vitamins: Small Nutrients With Big Jobs
The B-complex family includes thiamin, riboflavin, niacin, vitamin B6, pantothenic acid, biotin, folate and vitamin B12.
Many B vitamins function as parts of coenzymes that help the body carry out metabolic reactions.
In simpler terms, they help the body use nutrients and keep normal metabolism running.
Thiamin is involved in carbohydrate metabolism and normal nervous system function.
Riboflavin participates in cellular metabolic reactions.
Niacin is involved in energy metabolism.
Vitamin B6 participates in amino acid metabolism.
Folate and vitamin B12 are involved in important processes associated with cell function and blood formation.
There is also a practical lesson here for pet food.
Certain vitamins can be damaged during food processing. Thiamin, for example, can be destroyed by high heat. Properly formulated foods take processing losses into consideration so that adequate amounts remain available in the finished product.
What matters is the nutrition in the finished food, not simply what sounded impressive before processing.
What About Vitamin C?
This one surprises a lot of people.
Humans need vitamin C from our diet because we cannot manufacture sufficient amounts ourselves.
Healthy dogs and cats are different.
Dogs and cats are capable of synthesizing vitamin C within their own bodies. Because of this ability, a dietary vitamin C requirement has not been demonstrated for normal dogs and cats.
Does that mean vitamin C is bad?
No.
It means that seeing vitamin C on a pet food or supplement label does not automatically make that product healthier or nutritionally superior.
Research has not established that routinely giving large amounts of supplemental vitamin C to healthy dogs and cats provides a general nutritional advantage, and excessive supplementation may be inappropriate in some clinical situations.
Context matters.
This is also a good reminder that human nutrition cannot simply be transferred directly to our pets.
Dogs are not humans.
Cats are not dogs.
Each species has its own nutritional physiology.
So, Should We Be Adding Vitamins to the Bowl?
There are absolutely situations where supplementation may be appropriate. An individual animal may have a medical condition, documented deficiency or specific nutritional need that requires veterinary guidance.
That is very different from assuming that adding vitamins to an already well-balanced diet will automatically make it healthier.
Properly formulated pet foods are designed to provide the vitamins dogs and cats require.
Adding more without understanding what is already present can upset the nutritional balance we were trying to improve in the first place.
This is the question I would rather pet owners ask:
"What does my pet actually need?"
That is a much better question than:
"What else can I add?"
The Body Does Not Read the Front of the Bag
Pet food marketing encourages us to focus on individual words.
- Added vitamins
- Antioxidants
- Superfoods
- Omega fatty acids
- High protein
Some of those things can certainly be valuable.
But none of them, by themselves, tell us whether a diet is nutritionally appropriate.
The body does not read marketing claims.
It responds to nutrients, their amounts, their availability and the way they interact with one another.
Good nutrition exists between two extremes: too little and too much.
That is why I believe understanding the bowl is far more useful than simply reading the promises on the bag.
What I Want You to Remember
You do not need to memorize vitamin chemistry to feed your dog or cat well.
But I do want you to remember one principle:
More nutrition is not necessarily better nutrition. Better balance is better nutrition.
Vitamin A is essential, but excess can become harmful.
Vitamin D is essential, but excessive amounts can also cause serious problems.
Vitamin E helps protect cells from oxidative damage.
Vitamin K supports normal blood clotting.
The B vitamins perform critical jobs throughout metabolism.
Healthy dogs and cats normally produce their own vitamin C.
And dogs and cats do not even handle every vitamin in exactly the same way.
At Purrs McBarkin’, this is why I believe pet nutrition should begin with education rather than marketing.
My goal is not to convince you that the food with the longest ingredient list, the biggest vitamin panel or the most impressive claims must be the best.
My goal is to help you better understand what is going into your pet's bowl, what those nutrients actually do and why balance matters.
Because when we understand the science, we can ask better questions.
And better questions lead to better decisions.
Feed with purpose, not guesswork.
This article is provided for general pet nutrition education and is not intended to diagnose, treat or replace the advice of your veterinarian. Dogs and cats with medical conditions or specific therapeutic nutritional needs should be evaluated individually.
Sources
- Case, L.P., Daristotle, L., Hayek, M.G., & Raasch, M.F. Canine and Feline Nutrition: A Resource for Companion Animal Professionals. 3rd Edition. Mosby/Elsevier. Chapter 5: Vitamins.
- Schweigert, F.J., Raila, J., Wichert, B., & Kienzle, E. “Cats Absorb Beta-Carotene, but It Is Not Converted to Vitamin A.” Journal of Nutrition. 2002; 132:1610S-1612S.
- How, K.L., Hazewinkel, H.A.W., & Mol, J.A. “Dietary Vitamin D Dependence of Cat and Dog Due to Inadequate Cutaneous Synthesis of Vitamin D.” General and Comparative Endocrinology. 1994; 96:12-18.
- Morris, J.G. “Cats Discriminate Between Cholecalciferol and Ergocalciferol.” Journal of Animal Physiology and Animal Nutrition. 2002; 86:229-238.
- Innes, J.R.M. “Vitamin C Requirements in the Dog: Attempts to Produce Experimental Scurvy.” Report of the Cambridge Institute of Animal Pathology. Cambridge, England. 1931.