When a Vitamin isn't a Vitamin At All
Pet owners ask me every day about supplementing a nutraceutical* for their pet's chronic condition. Some common examples are:
Heart disease - magnesium, Vitamin E, B vitamins, taurine, thiamin
Wound healing - zinc
Immunedeficiency - Vitamin A
Anemia - Vitamins B2, B6, iron, etc
Oxalate bladder stones - Vitamin B6
Asthma - Vitamin B6
Diabetes - magnesium
Immune-mediated diseases - Vitamin D
The difference between most people and most pets is that most pets are eating complete and balanced diets, and people do not. In fact, the majority of chronic problems experienced in the human population are likely due to some form of malnutrition, which may be why humans have a different set of common disorders than dogs and cats (such as atherosclerosis, diabetes, and hypertension). Every one of the conditions with suggested nutraceuticals listed above are used in people to correct a dietary deficiency.
Generally, supplementing dogs and cats with nutrients doesn't make much sense if they are eating a complete and balanced diet - at least if that nutrient is used in the human conditions to treat a deficiency. Yes, you need to know a bit of physiology to evaluate these compounds for use as medication.
On the other hand, I've seen a rise in the number of people feeding unbalanced homemade diets, so perhaps veterinarians should give these kinds of supplements a closer look in pets eating unbalanced diets. Or just encourage the owner to get them properly balanced.
But nutrients can have other effects, activities that show up only when pharmaceutical doses are used. When nutrients are used at doses beyond what is necessary for nutritional maintenance, they are being used as nutraceuticals. And some do have interesting potential. One well known example is the use of Vitamins A, E, C, and pyridoxine as antioxidants. Another is the use of fish oil in higher than nutritional doses to suppress chronic inflammation.
Moral of the story - it's hard to decide if a nutraceutical will help a pet with a chronic problem without direct evidence, like a study involving that nutrient, for that condition, in a group of similar patients, compared to patients taking a placebo. But studies are expernsive, and we can't usually count on getting all of the studies we need. If the scientific support is lacking but the supplement seems safe and the mechanism makes sense, a veterinarian may choose to use a nutraceutical. But it's just not as simple as searching the web and picking the most common recommendations that can be found.
*A nutraceutical is a nutrient used at supra-nutritional doses. Herbs are not nutraceuticals.