Vitamins

Vitamins

A vitamin is an organic compound essential as a nutrient in small quantities for an organism. Specifically, a chemical compound (or related set of compounds) is termed a vitamin when an organism cannot synthesize it in adequate amounts and must acquire it from the diet.

Therefore, the designation of a substance as a vitamin depends on both the circumstances and the specific organism. For instance, ascorbic acid (vitamin C) is classified as a vitamin for humans but not for most other animals, and biotin and vitamin D are necessary in the human diet only under certain conditions.

Conventionally, the term "vitamin" excludes other vital nutrients like dietary minerals, essential fatty acids, or essential amino acids (which are required in larger quantities than vitamins), and it does not encompass the numerous other nutrients that promote health but are needed less frequently. Currently, thirteen vitamins are universally recognized.

Vitamins are essential for normal growth and development of the body. There are 13 essential vitamins: A, C, D, E, K, and the B vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, vitamin B-6, vitamin B-12, and folate). Typically, these vitamins are obtained from the diet, although the body can synthesize vitamins D and K. Individuals following a vegetarian diet may require a vitamin B12 supplement.

The classification of vitamins is based on their biological and chemical activity rather than their structure. Consequently, each "vitamin" encompasses a range of vitamer compounds that exhibit the biological activity associated with that vitamin. These chemicals are grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A," which includes compounds like retinal, retinol, and four known carotenoids. Vitamers can be converted into the active form of the vitamin in the body and may sometimes convert to each other.

Vitamins serve diverse biochemical functions. Some act as hormone-like regulators of mineral metabolism (e.g., vitamin D) or regulators of cell and tissue growth and differentiation (e.g., certain forms of vitamin A). Others function as antioxidants (e.g., vitamin E and sometimes vitamin C). The majority of vitamins (e.g., B complex vitamins) serve as precursors for enzyme cofactors, aiding enzymes in their metabolic functions. Vitamins may bind tightly to enzymes as part of prosthetic groups, or they may be loosely bound as coenzymes, facilitating chemical reactions between molecules.

Before the mid-1930s, vitamins were obtained solely from food, and dietary changes could affect the types and amounts of vitamins consumed. Since the mid-20th century, vitamins have been produced as commodity chemicals and are widely available as inexpensive semi-synthetic and synthetic-source multivitamin dietary supplements.

The term "vitamin" was coined by Polish scientist Casimir Funk, who combined "vital" and "amine," suggesting in 1912 that organic micronutrients preventing beriberi and similar dietary-deficiency diseases might be chemical amines. This proved inaccurate for the micronutrient class, and the term was shortened to "vitamin."

Each vitamin performs specific functions, and deficiency in certain vitamins can lead to deficiency diseases. For example, insufficient vitamin D intake can cause rickets. Some vitamins may help prevent medical conditions; for instance, vitamin A prevents night blindness.

The best way to obtain sufficient vitamins is through a balanced diet with a variety of foods. In some cases, a daily multivitamin may be necessary for optimal health, although excessive doses of certain vitamins can have adverse effects.