Overview

A vitamin is an organic chemical compound required in small amounts for the human body to perform vital biochemical functions. The term covers a group of distinct molecules that the body cannot synthesise in sufficient quantities and therefore must obtain from the diet or other external sources. Scientists currently recognise thirteen vitamins, which are conventionally named by letters and, in the case of the B complex, by numbers: Vitamin A, several B1, B2, B3, B6, B12 and other B vitamers, Vitamin C, Vitamin D, Vitamin E, and Vitamin K. For example, citrus fruits such as oranges and lemons are well known sources of vitamin C.

Classification and chemical forms

Vitamins are classified by biological activity rather than by shared chemical structure. Many vitamins exist as several related molecules called vitamers; these interconvertible forms are precursors or active derivatives that show the same essential activity in the body. Broadly, vitamins fall into two categories: fat-soluble and water-soluble. Fat-soluble vitamins (notably A, D, E, and K) can be stored in liver and adipose tissue and released when needed. Water-soluble vitamins include the vitamin B complex (B1, B2, B3, B6, B12, etc.) and vitamin C, which are not stored extensively and are eliminated more rapidly.

Biological roles and examples

Vitamins act as coenzymes, antioxidants, signalling molecules or structural precursors that support metabolism, growth and maintenance. For example, vitamin A contributes to vision and epithelial health; several B vitamins participate in energy metabolism and nervous system function; vitamin C is important for connective tissue synthesis and immune responses; vitamin D supports calcium balance and bone health; vitamin E functions as a lipid-soluble antioxidant; and vitamin K is essential for certain blood-clotting proteins. While vitamins are distinct from other essential nutrients such as minerals, essential fatty acids and amino acids, they work together with those nutrients to maintain physiological function. Many vitamins are plentiful in a varied food supply, including fruits, vegetables, grains, dairy and animal products.

History and discovery

The concept of vitamins emerged in the early 20th century as researchers linked specific deficiency disorders to the absence of dietary factors. The word "vitamine" was coined in 1912 by Casimir Funk to describe these vital amines; the final "e" was later dropped after it became clear not all such factors were amines. Over the decades, nutritional biochemistry identified individual vitamins, their chemical identities and the consequences of their lack. The study of deficiency diseases helped drive this work, and many public-health advances—like food fortification and dietary recommendations—followed from that discovery process.

Deficiency, excess and public-health importance

A short-term shortage of a vitamin may have little immediate effect if body stores exist, but prolonged inadequate intake or impaired absorption can lead to characteristic deficiency diseases. Classic examples include scurvy from vitamin C deficiency, beriberi associated with thiamine (B1) deficiency, and rickets linked to inadequate vitamin D during bone growth. Conversely, excessive intakes—particularly of fat-soluble vitamins—can cause toxicity because these compounds accumulate in tissues. Public-health measures such as fortifying staple foods, promoting diverse diets and targeted supplementation reduce the burden of deficiency worldwide.

Supplements, fortified foods and practical guidance

Vitamins are available as single preparations or combined in multivitamin supplements and are produced by a range of manufacturers and drug companies. Supplements can prevent or correct deficiencies in at-risk groups, such as pregnant people, older adults, those with restricted diets, or people with certain malabsorption conditions. However, in populations with access to varied diets, routine high-dose supplementation is often unnecessary and can sometimes be harmful. Health authorities typically recommend obtaining nutrients primarily from a balanced food pattern, using fortified products or supplements when indicated, and consulting healthcare professionals for individual advice.

  • Key distinctions: vitamins are organic micronutrients distinct from minerals, essential fatty acids and amino acids.
  • Solubility: fat-soluble (A, D, E, K) versus water-soluble (B complex and C) affects storage and toxicity risk.
  • Historical note: the term originated with Casimir Funk and the early 20th-century search to prevent deficiency diseases.
  • Everyday examples: citrus fruits like oranges and lemons are vitamin C sources; sunlight enables production of vitamin D in skin.