Cofactors and vitamins


  1. Role of vitamins in metabolism
  2. The difference between fat soluble and water soluble vitamins
  3. Different types of vitamin reference values

Role of vitamins in metabolism as cofactors of enzymes

Almost all biochemical reactions, that ongoing in the human body, require a corresponding biological catalyst – an enzyme.

The most of enzymes are proteins.

Many enzymes have to link to their respective helpers to promote optimal arrangement of their atoms and proper functioning. Such helpers refer as cofactors.

Two sorts of helper molecules are:

  1. inorganic ions;
  2. complex non-protein organic molecules – coenzymes.

Examples of inorganic helper molecules include magnesium (Mg++), selenium (Se++) and iron (Fe++).

The main atoms in a structure of organic helper molecules, coenzymes, are carbon and hydrogen.

Vitamins serve as the basis for coenzymes and work with enzymes to accomplish metabolic reactions.

Some vitamins act as coenzymes and don’t require any modifications. Others are precursors to coenzymes.

The primary role of vitamins in metabolism is in assisting a transformation of different types of biomolecules.

Many enzymes do not work partially or completely if they are not associated with certain non-protein helper molecules.

Different types of vitamins can connect to their enzymes in two ways - either through ionic or hydrogen bonds (for a short time) or through stable covalent bonds (permanently).

The most common sources of coenzymes are vitamins derived from food. They are very important nutrients that organism needs in limited amounts.

Cofactors, coenzymes, and vitamins

The main difference between fat soluble and water soluble vitamins

Water soluble vitamins

Water soluble vitamins can be directly absorbed from the intestine into the bloodstream.

The water soluble vitamins are vitamin C (ascorbic acid) and vitamin B group.

Because excess amounts of these vitamins are excreted in the urine, it is unlikely to overdose them and to reach toxic levels in the body.

Fat soluble vitamins

Fat soluble vitamins enter the body in the same manner as lipids and therefore a small amount of fat intake along with them is essential for their better absorption. 

Fat soluble vitamins include A (retinol), D (calciferol), E (α-tocopherol), and K (phylloquinone). They readily pass through the plasma membranes of the gastrointestinal tract and other tissues.

The main difference between fat soluble and water soluble vitamins is that the excessive consumption of fat soluble vitamins can lead to the fact that they accumulate in the fatty tissues of the body and reach toxic levels. It is especially important to take them properly in supplements to prevent fat soluble vitamins overdose.

Different types of vitamins
 Water soluble Fat soluble

C (Ascorbic acid)

B1 (Thiamine)

B2 (Riboflavin)

B3 (Niacin, Niacinamide, Nicotinic Acid)

B5 (Pantothenic acid)

B6 (Pyridoxine, Pyridoxal 5'-phosphate)

B7 (Biotin)

B9 (Folic acid)

B12 (Cobalamin)

A (retinol)

D (calciferol)

E (α-tocopherol)

K (phylloquinone) 


Cofactors and coenzymes

Different types of vitamin reference values

The Food and Nutrition Board of the US Institute of Medicine established several different types of reference values for healthy nutrition guidelines:

Recommended dietary allowance (RDA)

Recommended dietary allowance is the average day-to-day dietary intake level of a nutrient sufficient to meet the needs of almost any healthy person based on age and gender.

Adequate intake (AI)

Adequate intake is a recommended intake value based on observed or experimentally determined estimates of nutrient intake by a group of healthy people that are assumed to be sufficient.

Adequate intake is established when recommended dietary allowance cannot be determined.

Tolerable upper intake level (UL)

Tolerable upper intake level is the highest level of daily intake of a specific nutrient which probably does not pose a risk of adverse health effects in almost all individuals of a specified age and gender. 

Exceeding this level may lead to vitamin overdose.