Vitamins

Vitamins are organic compounds required by the human body in small amounts but which the body cannot synthesize in sufficient quantity on its own. For this reason, they must be obtained from food or supplements. Vitamins do not provide energy in the way carbohydrates or fats do; instead, they participate in chemical processes within cells, often functioning as coenzymes.

Various vitamins are recognized and typically referred to by letters and chemical names—for example, vitamin C (ascorbic acid) and vitamin A (retinol). The B group comprises several distinct compounds, including B1 (thiamine), B2 (riboflavin), B3 (niacin), B6, B9 (folate), and B12 (cobalamin).

Classification: fat-soluble and water-soluble

Vitamins are divided into two groups according to their solubility. Fat-soluble vitamins—A, D, E, and K—can be stored in body fat and organ tissue, which means the body can maintain reserves over long periods, but excessive intake may also be harmful. Water-soluble vitamins—the B group and C—are generally not stored easily, and most excess amounts are excreted in urine, meaning they must be replenished regularly.

Functions in the body

Each vitamin has specific roles. Vitamin A relates to vision and the health of skin and mucous membranes. Vitamin D is involved in calcium absorption and bone health; the skin can produce some vitamin D when exposed to sunlight. Vitamin K participates in blood coagulation. Vitamin C contributes to collagen synthesis and reduces oxidation. The B group generally functions as helpers in energy metabolism and various metabolic processes.

Deficiency and associated diseases

When a particular vitamin is absent from the diet for extended periods, health symptoms can develop. Well-known examples include scurvy (vitamin C deficiency), rickets and weakened bones (vitamin D deficiency), beriberi (B1 deficiency), pellagra (B3 deficiency), and certain types of anemia linked to B12 or folate deficiency. Vitamin A deficiency can affect vision.

Natural sources and supplementation

Natural sources are diverse foods: vegetables and fruits, grains and whole grains, legumes, meat, fish, eggs, and dairy. Vitamin B12 is found mainly in animal products; therefore, those following plant-based diets are often advised to use supplements or fortified foods. Many countries add vitamins to staple foods (such as grain or cooking oil) to prevent disease in the wider population. Excessive intake of supplements, particularly fat-soluble vitamins, can cause toxicity (hypervitaminosis).