Vitamins are organic compounds that are needed in small amounts in the body for carrying out essential processes. The majority of vitamins required by the body need to be consumed in the diet as they can't be produced in the body. Only small amounts of vitamins are required, in milligrams (mg) or micrograms (µg).
Vitamins carry out a range of functions in the body with some involved in enzyme activity, while others act as antioxidants (preventing oxygen from doing damage in the body).
Vitamins can be separated into two groups; water soluble vitamins (Vitamin C, B Vitamins) and fat soluble vitamins (Vitamin A, D, K). Water soluble vitamins are carried in the body in the blood, excreted in the urine, needed in regular small doses and are unlikely to reach toxic levels in the blood. Fat soluble vitamins are absorbed into the lymph system, then carried into the blood by protein carriers, stored in the body fat and are more likely to be toxic when consumed in excess of the body's requirements.
Vitamins used to be referred to by letters (e.g. A, B, C,) but are now more often referred to by their chemical name. Both will be listed in the following links.