Vitamins can be divided into two main groups depending on whether they are soluble in fat or water. In addition, there is a group of vitamin-like substances that are similar to vitamins without fitting exactly into the categories.

Substances must have five basic characteristics in order to be classified as vitamins:

• It must be an organic compound different from fat, protein and carbohydrate.
• It must be a component of the diet.
• It must be essential in minute amounts for normal physiological function.
• Its absence must cause a deficiency syndrome.
• It must not be synthesized in quantities sufficient to support normal physiological function.

Individual vitamins

VITAMIN A

Vitamin A is required for:

• normal vision
• healthy coat
• healthy skin
• healthy mucous membranes
• healthy teeth

VITAMIN D

The primary function of vitamin D has to do with calcium and phosphorus and includes:

• enhancement of intestinal absorption and mobilisation
• retention and bone deposition

VITAMIN E

Vitamin E exists in different forms of which alpha-tocopherol is the most active form. Alpha-tocopherol functions as:

• a powerful biological antioxidant
• an aid to maintain membrane integrity

The body produces harmful free radicals (oxidants) that cause damage to the cells as a by-product of normal metabolism. Free radicals weaken the immune system, accelerate signs of ageing and have an important role in the development of many different diseases. The biologically active antioxidants, of which vitamin E is one of the most significant, can protect the body from the harmful effects of free radicals, if the levels of antioxidants are high enough.

VITAMIN K

Vitamin K is synthesised by gut bacteria, and regulates the formation of several blood-clotting factors.

VITAMIN B COMPLEX

The individual B-vitamins have specific functions but overall they:

• act as components of enzymes,
• act as co-factors in the metabolic processes.

VITAMIN C

Because vitamin C can be synthesised from glucose in the body of healthy dogs and cats it is not technically essential. However, more recent research has shifted the focus from prevention of deficiency to the treatment and prevention of disease. Vitamin C plays an important role in immune function.