Basics of Nutrition: Vitamin Guide for Dog and Cat Owners

Vitamins are essential helpers for enzymes and hormones to work in the body. They are not an energy source, and most of them are not produced in the body. 

There are two types of vitamins based on their solubility. 

• Fat-soluble vitamins: A, D, E, and K

• Water-soluble vitamins: C and the B-complex group

Let’s take a closer look at why these nutrients are so vital for your dog or cat.

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Fat-Soluble Vitamins

Together with dietary fat, these vitamins are absorbed and primarily stored in the liver. Overdosing can be harmful because they build up, particularly with vitamins A and D.

Vitamin A

Vitamin A is also referred to as retinol, retinoic acid, or retinal. 

Functions include skin and tissue health, bone growth, vision, and reproduction. It supports the formation of healthy epithelial cells. This is important for mucosal membranes and protects cells from bacterial invasion in the mucosal barrier. 

Signs of deficiency include poor growth, skin issues, night blindness, and compromised immunity.

Sources include milk, liver, egg yolks, sweet potatoes, carrots, and fish liver oils.

Note: Dogs can convert plant carotenoids, such as beta-carotene, into vitamin A, but cats require preformed vitamin A from animal-based diets because they lack an enzyme called B carotene 15,15-dioxygenase.  Vitamin A may have function in weight management as well. 

Here is the figure for Beta-carotene conversion into vitamin A. 

Vitamin D

As with vitamin A, vitamin D has provitamin forms of it.

These are forms of vitamin D2 and D3. This vitamin's D2 form is created when ergosterol is exposed to ultraviolet light. Ergosterol is common in plant tissue and is exposed when it is broken down. D2 is obtained by herbivores from sun-dried or irradiated plants. Vitamin D3 is essential for the majority of species, especially carnivores and omnivores like dogs and cats. Vitamin D3 can be produced by the body from 7-Dehydrocholesterol with UV exposure on the skin. 

Here is the reaction that happens during UV exposure to the skin. 

Nevertheless, this vitamin can be stored as vitamin D3. The kidney produces calcitriol, which is the active form of vitamin D3. Skin-produced D3 first travels to the liver and subsequently the kidneys. PTH (paraathyroid hormone) levels rise and the kidneys encourage calcitriol when the body requires greater absorption. 

Functions: Maintains healthy bones and teeth by controlling calcium and phosphorus. Some consider this vitamin a hormone due to its functions because active version is produced in body. 

Deficiency signs: Rickets in young pets and osteomalacia (soft bones) in adults.

Sources: Fish liver oils, egg yolk, liver, sunlight. Most commercial pet foods are enriched with vitamin D3. 

Special note: Cats and dogs cannot make enough vitamin D from sunlight alone—dietary sources are essential.

Vitamin E

Vitamin E is also known as a chemical group called tocopherols. The most potent version is alpha-tocopherol. It is a very powerful antioxidant. It is often used as an antioxidant in food systems. It is stored in the bilayer of the cell membrane and liver. 

Functions: A powerful antioxidant that protects cells from damage and supports immune health.  It donates electrons in the lipid peroxidation reaction, where it protects polyunsaturated free fatty acids (PUFAs).  It protects free fatty acids and sulfur-containing amino acids as well. 

There is also a relationship with vitamin E and selenium. Selenium is a cofactor for the enzyme glutathione peroxidase, which reduces peroxides from fatty acid oxidation. Selenium can spare vitamin E and vice versa. 

Deficiency signs: Reproductive failure, muscle weakness, or (in cats) fat inflammation known as pansteatitis.

Sources: Wheat germ, soybean, corn, and sunflower oils.

Vitamin K

Vitamin K is also known as group called quinones. Vitamin K1 (phylloquinone) occurs naturally in green plants. Vitamin K2 (menaquinone) is produced by bacteria in the large intestine. Vitamin K3 (menadinone) is the most commonly found sythetic versions. 

Functions: Essential for blood clotting and it is required in liver's production of prothrombin and other 3 more of its factors.  and bone health.

Signs of a deficiency include excessive bleeding or delayed clotting.

Sources include liver, certain fish dishes, and green leafy vegetables.

Special note: Pets' gut bacteria may produce less vitamin K as a result of antibiotic treatments.

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Water-Soluble Vitamins

With the exception of vitamin B12, these are not stored in the body like fat-soluble vitamins are. Deficits occur more quickly because they are rapidly absorbed and eliminated in urine, but toxicities are uncommon.

B-Complex Vitamins

Vitamins in the B group support cell growth, aid in the body's use of food as fuel, and preserve the health of the blood and nerves.

Thiamin (B1): Important for carbohydrate metabolism and nervous system function. The requirement level depends on how much carbohydrate is taken into the body. It is abundantly found in pork, beef, liver, wheat germ, whole grains, and legumes. It is a heat-labile enzyme, which means it can be destroyed by heat. In pet food, it should be supplemented because deficiency is rare and related to other factors in the body. 

Riboflavin (B2): It is yellow colored vitamin. it is heat stable but destroyed in light. This vitamin aids in the release of energy from food and promotes the health of the skin and coat. It is found in organ meat, milk, whole grains and vegetables. 

Niacin (B3): Aids fat, protein, and carbohydrate metabolism. When absorbed, it turns into nicotinamide. Then, it is converted into two different forms, NAD and NADH, which serve as hydrogen donors in the cell's energy reactions. Dogs can make niacin from tryptophan, but cats cannot. Its free form is abundant in meat. It is also common in plant tissue, but it is not accessible mainly for the body. 

Vitamin (B6) (Pyridoxine): it has 3 forms, and it is involved in reactions of amino acids for transamination, deamination, and decarboxylation reactions. It is crucial for the metabolism of proteins and the synthesis of hemoglobin. It can help tryptophan turn into niacin. Vitamin B6 is commonly found in organ meats, wheat germ, and whole grains. there is no natural dietary deficiency reported. 

Pantothenic Acid: Supports energy production through the citric acid cycle. It is phosphorylated in the body by ATP to form coenzyme A. This coenzyme is universal in many reactions regarding carbohydrate, fat, and protein metabolism. Deficiencies are extremely rare and it is commonly found in organ meat, egg yolk, dairy products, and legumes. 

Biotin: Important for skin, coat, and fatty acid metabolism. It carries CO₂ to reactions where the carbon chain needs to be extended. Therefore, it is crucial for synthesis reactions. It is commonly found in egg yolk, and eggs must be cooked because egg white has an enzyme called avidin, which binds biotin. Cooking destroys the enzyme and makes biotin available. It is also found in liver, milk, legumes, and nuts. Intestinal bacteria can also produce it. 

Folic Acid: Necessary for DNA synthesis and red blood cell production. It has an important role in the production of the nucleotide thymidine. It is found in green leafy vegetables and organ meats such as liver and kidney. It can be fermented in the body as well by bacteria. 

Cobalamin (B12): Vital for nerve function and red blood cell health; stored in the liver. It is the only vitamin contains a trace element. It facilitates carbon transfer like folic acid. It is crucial for myelin synthesis. It is only found in foods of animal origin. 

Choline: Supports fat metabolism, cell membranes, and neurotransmitter function. It acts as a donor of methyl units from various parts of the body. It is also necessary for normal fatty acid to be transfered within cells. It is also a part of cell membrane, particularly lecithin. Many animals are capable of synthesizing choline from amino acid serine. 

Vitamin C (Ascorbic Acid)

Vitamin C can be easily oxidized in the body. It is sensitive to heat, light, alkalines, and oxidative stress. 

Functions: Supports collagen formation, wound healing, and antioxidant defense. the body uses it for hydroxilation of the amino acids proline and lysine in the formation of collogen. 

Special note: Dogs and cats can produce their own vitamin C, so dietary supplementation is usually unnecessary. Deficiency can cause scurvy. 

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