12.1 Basics of Vitamins

Figure 12.1: Two Classes of Vitamins

Vitamins can be divided into two classes: water-soluble vitamins and fat-soluble vitamins (as seen in figure 12.1).

Vitamin bioability is also affected by three factors:

1. Absorption

   

   Figure 12.2: Mechanism of Absorbing Vitamins

   Vitamins must be absorbed by the body in order to perform their functions (see figure 12.2). About 40% to 90% of vitamins are absorbed in the small intestine.

   

   Figure 12.3: Mechanisms Involved in Absorbing Water-Soluble Vitamins

   Fat-soluble vitamins requrie fat in the diet to be absorbed, and water-soluble vitamins may require transport molecules or specific molecule in the GI tract to be absorbed.

2. Transport

   Water-soluble vitamins are transported by blood proteins; fat-soluble vitamins are transported by chylomicrons.

3. Conversion

   Some vitamins are absorbed in their inactive form (i.e., as a provitamin or a vitamin precursor) - they must be converted into active forms by the body.

12.1.1 Cofactors

Figure 12.4: Classes of Cofactors

A cofactor is a non-protein chemical compound that is bound to a protein and is required for biological activity.

Cofactors can also be divided into two categories (see above figure 12.4).

Figure 12.5: Vitamins as Cofactors

Like mentioned at the beginning of this chapter, vitamins (at least some of them) also form a part of the coenzymes that enable enzymes to either compounds or to catabolize compounds (as seen in figure 12.5).