Vitamin

Vitamins are a group of organic nutrients, required in small quantities for a variety of biochemical functions that, generally, cannot be synthesized by the body and must therefore be supplied in the diet.



Vitamins are organic nutrients with essential metabolic functions that are required in small amounts in the diet because they cannot be synthesized by the body. The lipidsoluble vitamins (A, D, E, and K) are hydrophobic molecules requiring normal fat absorption for their absorption and the avoidance of deficiency.

■ Vitamin A (retinol), present in meat, and the provitamin (β-carotene), found in plants, form retinaldehyde, utilized in vision, and retinoic acid, which acts in the control of gene expression.
■ Vitamin D is a steroid prohormone yielding the active hormone calcitriol, which regulates calcium and phosphate metabolism; deficiency leads to rickets and osteomalacia. It has a role in controlling cell differentiation and insulin secretion.
■ Vitamin E (tocopherol) is the most important lipid-soluble antioxidant in the body, acting in the lipid phase of membranes protecting against the effects of free radicals.
■ Vitamin K functions acts as the cofactor of a carboxylase that acts on glutamate residues of precursor proteins of clotting factors and bone and other proteins to enable them to chelate calcium.

The water-soluble vitamins act as enzyme cofactors. While the lipid-soluble vitamins are hydrophobic compounds that can be absorbed efficiently only when there is normal fat absorption.