vitamiin

A vitamin is an essential, organic micronutrient required in small amounts for normal metabolism, growth, and development. Humans cannot synthesize enough of most vitamins and must obtain them from the diet or supplements. They are involved in a range of biochemical functions, including energy production, DNA synthesis, and immune support.

Vitamins are commonly classified as fat-soluble or water-soluble. Fat-soluble vitamins A, D, E, and K dissolve in fats and are stored in body tissues; they can accumulate and may cause toxicity at high intakes. Water-soluble vitamins, including vitamin C and the B-complex vitamins, dissolve in water and are typically excreted in urine; they are required more regularly and have lower storage in the body.

Functions often involve acting as coenzymes or precursors for enzymes, enabling metabolic reactions. Some vitamins serve as antioxidants (e.g., vitamins C and E); others regulate gene expression, immune function, or bone health (e.g., vitamin D).

Dietary sources vary by vitamin. Fresh fruits, vegetables, grains, dairy, eggs, meat, and fortified foods can provide many vitamins. Some vitamins can be synthesized in small amounts by the body or through exposure to sunlight (vitamin D) or gut microbiota (limited contributions for some B vitamins).

Deficiency can lead to specific diseases such as scurvy (vitamin C), rickets (vitamin D), and beriberi (vitamin B1). Toxicity is possible for certain fat-soluble vitamins with excessive intake. Recommendations vary by age, sex, life stage, and health status, and are provided by health authorities as dietary reference intakes.