Vitamins are organic substances required by the body in minute amounts as essential enzymes, enzyme precursors, or coenzymes for many of the body's metabolic processes. Most vitamins can not be synthesized by the body and need to be supplied with the food in sufficient quantities.
Vitamins are divided into two groups:
- Fat soluble:
The fat soluble vitamins (A, D, E and K) are are absorbed in the same way as dietary fats. Excess amounts are stored primarily in the liver and most metabolites are excreted in the feces through bile. Because they can be stored in theliver, dietary deficiencies of fat soluble vitamins develop much more slowly than those of water soluble ones.
- Water soluble:
Water soluble vitamins are generally absorbed passively in the small intrestine and excess amounts as well as metabolites are excreted in the urine. Except for cobalamin (vitamin B12), the body is unable to store water soluble vitamins, so it is important that the body can absorb them daily in appropriate amounts.
Fat soluble vitamins
Vitamin A (Retinol, beta carotene as precursor)
Effects: Vision, appetite, maintenance of the skin and coat. Natural beta carotene (which the body converts to vitamin A based on its needs) has antioxidant activity. In supplements, the natural form is identified by descriptions like "from D. salina", "from an algal source", "from a palm source", or as "natural beta-carotene" on the label. The synthetic form is identified only as "beta-carotene".
Deficiency: Signs include decreased vision, skin lesions, and abnormal bone growth.
Toxicity: Signs include abnormal bone remodeling, lameness, and death.
Stability: Beta carotene (originates exclusively from plant sources but is readily converted by the dog's metabolism) is one of the most stable and active vitamins in foods. The compound is sensitive to heat but significant losses only occur after long periods of boiling. Animal food sources contain active vitamin A.
Sources: Liver, fish liver oil, carrots, green leafy vegetables, egg yolks, yellow fruits. The more intense the color of a fruit or vegetable, the higher the beta-carotene content.
Vitamin D (Calciferol)
Effects: Promotes the body's absorption of calcium, which is essential for normal development and maintenance of healthy teeth and bones. It also helps maintain adequate blood levels of calcium and phosphorus. Can be manufactured by the body under sufficient exposure to UV radiation. Ten to 15 minutes of sunshine 3 times weekly is adequate to produce the body's requirement of vitamin D.
Deficiency: Signs of deficiency include bone malformations (rickets) characterized by bowing of the legs, thickening of the joints, and an increased incidence of fractures.
Toxicity: Excessive vitamin D supplementation can result in increased calcium absorption from the intestines. This can cause increased calcium resorption from the bones, leading to elevated levels of calcium in the blood. Elevated blood calcium may contribute to calcium deposition in soft tissues such as the heart and lungs. This can reduce their ability to function. Kidney stones, vomiting.
Stability: Stable in food storage, cooking and processing.
Sources: Vitamin D is only found naturally in animals and animal products. Halibut and cod liver oil, saltwater fish, cheese, yogurt, eggs.
Vitamin E (Tocopherol)
Effects: Acts as a biological antioxidant, and is required for normal reproduction. There are several forms of vitamin E. The most biologically active form is know as alpha-tocopherol, which should be supplemented as alpha-tocopherol, alpha-tocopherol acetate, or alpha-tocopherol succinate. Other forms, like gamma-tocopherol or beta-tocopherol, do not provide the same level of protection. Vitamin E from natural sources is labeled as alpha tocopherol or d-alpha tocopherol - dl-alpha tocopherol indicates a synthetic, less effective product. Do not give cheap vitamin E supplements that contain high levels of vitamin A, since this could lead to an overdose of vitamin A and possibly vitamin A toxicity. Vitamin E is also important for the formation of red blood cells and it helps the body to utilize vitamin K.
Deficiency: A deficiency of vitamin E can lead to decreased reproductive performance, retinal degeneration, and impairment of the immune system.
Toxicity: None known, but high levels of vitamin E can adversely affect the absorption of vitamins A and K, causing deficiencies. In the case of vitamin K this can interfere with normal blood clotting.
Stability: Vitamin E is sensitive to heat, light and oxygen and significant losses have been found after relatively short times of food storage.
Sources: Wheat germ, corn, nuts, seeds, spinach and other green leafy vegetables, asparagus, vegetable oils.
Vitamin K (Naphthoquinone)
Effects: Required for blood clotting. The bacteria present in the healthy intestine can synthesize all the vitamin K the body needs, so supplementation is generally not necessary.
Deficiency: Very rare, but occurs when there is an inability to absorb fats or the vitamin from the intestinal tract. Can also occur after prolonged treatment with oral antibiotics. Increased tendency to bruise and bleed.
Toxicity: None known.
Stability: Relatively stable to heat, but sensitive to acid, alkali, light and oxidizing agents.
Sources: Cabbage, cauliflower, spinach and other green leafy vegetables, cereals, soybeans, and other vegetables. Also producecd by the bacteria in the healthy gastrointestinal tract.
Water soluble vitamins
Vitamin B1 (Thiamine)
Effects: Conversion of carbohydrates into energy, essential for
the functioning of the heart, muscles, and nervous system.)
Deficiency: Signs include incoordination, weakness, seizures and
nerve damage. Brain damage can occur from severe
deficiency.Typically caused by a diet of raw fish which contains
Stability: Sensitive to heat, alkali, oxygen and radiation and
considerable amounts of the vitamin can be lost during
Sources: Wheat germ, rice and other whole grains, lean meats
(especially pork), liver, fish, yeast, dried beans, peas, and
Vitamin B2 (Riboflavin)
Effects: Plays a role in many enzyme reactions of the metabolism.
Also important for growth, red blood cell production, maintenance
of skin and coat, breakdown of protein, fat and carbohydrates.
Deficiency: Signs include decreased reproductive performance, dry
skin, weakness, and anemia.
Stability: Sensitive to light but heat stable.
Sources: Lean meats, liver, fish, eggs, yeast, cheese, legumes,
nuts, green leafy vegetables.
Vitamin B3 (Niacin)
Effects: Assists in the functioning of the digestive system, skin,
and nerves and is also important for the conversion of food to
energy. The amino acid tryptophan is a provitamin of niacin.
Deficiency: Signs include loss of appetite, bad breath, increased
salivation, diarrhea and emaciation.
Toxicity: Large doses of niacin can cause liver damage, peptic
ulcers, and skin rashes.
Stability: Stable to light, heat, air and alkali.
Sources: Liver, lean meat, poultry, fish, nuts, yeast, legumes,
asparagus, seeds, green leafy vegetables.
Vitamin B5 (Pantothenic Acid)
Effects: Important in many enzyme reactions in metabolism and the
synthesis of hormones.
Deficiency: None known.
Stability: Easily destroyed by heat in acidic or alkaline
conditions, but is stable in a neutral solution.
Sources:Eggs, fish, lean beef, legumes, yeast, broccoli and other vegetables in the cabbage family, white and sweet potatoes.
Vitamin B6 (Pyridoxine)
Effects: Prevents skin conditions and nerve problems, supports the
synthesis of antibodies by the immune system, helps maintain
normal nerve function, and acts in the formation of red blood
cells and in protein metabolism.
Deficiency: Signs include anemia, and seizures.
Stability: Quite stable to heat but sensitive to air, UV light and
Sources: Meat, fish, eggs, bananas, whole grains, but the average
diet already supplies adequate quantities.
Vitamin B8 (Biotin)
Effects: Essential for the protein and fatty acid metabolism.
Occurs in 8 different forms but only one of these, D-biotin, is
found in nature and has full vitamin activity.
Deficiency: None known, but may occur if a high quantity of raw
egg whites (which contain avidin) are consumed. Does not occur if
whole raw or cooked eggs are fed.
Stability: Quite stable to heat, most of the cooking losses are
due to biotin leaching into the cooking water.
Sources: Foods that are good sources of B vitamins.
Vitamin B9 (Folic Acid, Folate)
Effects: Along with vitamin B12 and vitamin C folic acid helps to
digest and utilize proteins, to synthesize new proteins when
needed, and aids tissue growth and cell function. It is also
necessary for the production of red blood cells and the synthesis
Deficiency: Signs of deficiency include anemia, and bone marrow
Stability: Very unstable, considerable losses occur during short
storage and cooking.
Sources: Carrots, yeast, liver, egg yolks, melon, apricots,
pumpkin, beans, rye and whole wheat, green leafy vegetables.
Vitamin B12 (Cobalamin, Cyanocobalamin)
Effects: Important in the formation of blood and the maintenance
of the nervous system.
Deficiency: only observed as an inherited disorder seen in some
Giant Schnauzers and Border Collies.
Stability: Stable to heat but sensitive to light, oxygen, acid and
Sources: Fish, liver, meat, poultry, eggs, cheese.
Vitamin C (Ascorbic Acid)
Effects: Vitamin C is synthesized in the liver by dogs. It is important in collagen synthesis, and in many other metabolic reactions, including proper functioning of the immune system. Since the dog's body produces Vitamin C, many pet food manufacturers and veterinarians state that it is not required in the food and that oversupplementation may be harmful. This is not true, and supplementation in an appropriate form (for example Ester-C, calcium ascorbate) can have beneficial effects on dogs suffering from chronic joint and musculoskeletal disorders. In puppies it helps to prevent the development of such disorders.
Deficiency: Signs of deficiency include impaired wound healing, greater susceptibility to infection (decreased immune function), muscle and joint pain.
Toxicity: None, vitamin C is water soluble and excess is regularly excreted by the body, but overconsumption may cause diarrhea since vitamin C is a natural laxative. Recent studies have shown that excessively high doses of vitamin C may contribute to the formation of kidney stones, and in very rare cases anemia caused by interference with vitamin B12 absorption.
Stability: Partially or completely destroyed by overcooking or long periods of storage as it is sensitive to heat, light and oxygen.
Sources: Citrus fruits, berries, tomatoes, cauliflower, potatoes, green leafy vegetables, green peppers.