Vitamin

What Is a Vitamin?

A vitamin is an organic compound that an organism requires in small quantities for proper metabolic function but cannot synthesize in sufficient amounts on its own. Because the body cannot make most vitamins — or makes them only in trace quantities — they must be obtained through diet or supplementation.

The word "vitamin" was coined in 1912 by biochemist Casimir Funk, who combined the Latin vita (life) with "amine," reflecting the early belief that all such compounds contained nitrogen. Although this turned out to be incorrect, the name stuck.

Classification

There are 13 recognized essential vitamins, divided into two broad categories based on solubility:

• Fat-soluble vitamins (A, D, E, K): Absorbed with dietary fat, stored in the liver and adipose tissue. Because they accumulate, excessive intake can lead to toxicity.
• Water-soluble vitamins (C and the eight B vitamins): Dissolve in water, are not stored in significant amounts, and excess quantities are generally excreted in urine. Regular dietary intake is therefore more critical.

Role in Health

Vitamins serve as coenzymes or precursors to coenzymes in enzymatic reactions, enabling processes such as energy metabolism, DNA synthesis, immune defense, and antioxidant protection. Deficiency of any vitamin leads to characteristic clinical syndromes — for example, vitamin C deficiency causes scurvy, vitamin D deficiency causes rickets, and vitamin B1 deficiency causes beriberi. Dietary Reference Intakes (DRIs) established by health authorities provide guidance on recommended amounts to prevent deficiency while avoiding toxicity.