Not only can you get in trouble with mineral supplements; vitamin supplements
can be dangerous also. Vitamins are required by the dog in minute amounts to
function as enzymes, enzyme precursors or co-enzymes in many of the dog's metabolic
processes. Vitamins fall into two general categories: water soluble (B-complex,
C) and fat-soluble (A,D,E,K). It is the fat-soluble vitamins that are dangerous
in excess, especially vitamins A and D.
- Vitamin A--The
origin of all vitamin A is the carotenoids in plants such as carrots, sweet
potatoes, deep green vegetables. Several carotenoids provide vitamin A; however,
beta-carotene is the most common in foods. Note that dogs can convert carotenoids
to active vitamin A, and therefore do not require animal sources of vitamin
A in their diets. Vitamin A is seldom found as a supplement because its components
(retinol, retinal and retinoic acid), are found in fish liver oils, milk,
liver and egg yolk. Excesses cause skeletal abnormalities and hyperesthesia.
- Vitamin D--
A protovitamin D, vitamin D3 is of importance to omnivores and carnivores.
Active vitamin D is synthesized by the dog's body thus generating a small
controversy over whether vitamin D should be classified as a hormone or as
a vitamin. Exposure of the dog to sunlight results in conversion of the precursor
7-dehydrocholesterol to cholecalciferol. Most foodstuffs contain very little
vitamin D, however fish liver oils, egg yolks and liver are good sources.
"Most commercially prepared pet foodsare enriched with vitamin D to ensure
that dogs and cats receive adequate amounts of this vitamin regardless of
the amount of daily sunlight they receive."
- Vitamin E--Vitamin
E, the biological, chain-breaking anti-oxidant not only neutralizes free-radicals,
but prevents the peroxidation of lipids within cellular membranes. Vitamin
E and selenium are synergistic. Optimum levels for the dog are still being
researched. Vitamin E is one vitamin with serious research behind it to support
its use as a supplement. It has been shown to ameliorate the pain of osteoarthritis
and recent research now shows thatit has an analgesic effect in the treatment
of rheumatoid arthritis as well. Its mode of action is the same as many NSAID's
in that it inhibits the enzyme cyclooxinase and prevents the formation of
inflammatory products. The form of Vitamin E is also important in terms of
its efficacy. All natural (RRR) Vitamin E is 50 % more bioavailable than the
- Vitamin K--This
vitamin is necessary for blood coagulation can is commonly given to dogs as
an antidote for anti-coagulant rat poisons. Dogs produce their own vitamin
K through bacterial synthesis in the intestine. Supplementation is not required.
Water Soluble Vitamins
All that needs to be said about water-soluble B-complex vitamins as they pertain
to canine nutrition is that the B-complex series of vitamins are seldom deficient
in dogs. It is possible to create a thiamin deficiency by feeding a diet of
raw fish, or a biotin deficiency by feeding large amounts of raw egg whites.
As the protein levels in the diet increase, the requirements for vitamin B6,
pyridoxine, increase, however a diet so concentrated in protein would be most
- Vitamin C
(Ester-C) The use of an exogenous source Vitamin C is controversial
because the dog is one of several mammals which has the ability to manufacture
ascorbic acid. (Though the dog makes the least amount of ascorbic acid per
kilogram of body weight of any animal who has that ability.) There is a definite
lack of peer reviewed citations with respect to its use in dogs. However,
one study mentioned in the Waltham book on nutrition does show that blood
plasma levels of vitamin C are dramatically reduced in dogs exposed to oxidative
stress. Oxidative stress can include exposure to toxins, which involve pesticides
and cigarette smoke, and exercise. Performance dogs would be especially benefit
from supplementation. Clinical trials do support its use for amelioration
of pain, but the efficacy seems to depend on the form in which this vitamin
is taken. Calcium ascorbate has a neutral pH so digestive upsets are avoided
and it appears not to be flushed out of the body as rapidly.
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