Vitamins: What They Are, Functions and Classification

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Louise Hay

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"Vitamin = amine of life": with this name the Polish scientist Casimir Funk identified, in 1912, a new organic compound essential to human life. Shortly thereafter new ones were identified Vitamins, up to 13 still known. 

Starting from the 30s, man began to reproduce vitamins of synthetic origin in the laboratory, completely similar to those present in nature (in this regard, read also: Vitamins between Past and Present).

This class of substances, essential to life, falls into the category of micronutrients. In fact, very small quantities of vitamins are required (in the order of milligrams or even micrograms) to satisfy the biological demands of the organism. However, although some of them are produced autonomously by our body, most of the vitamins must necessarily be introduced through thesupply. The quantities produced are in fact negligible and generally insufficient to cover the real needs of the organism; plants, on the other hand, are able to produce them independently and it is for this reason that foods of plant origin represent the most important vitamin resource for humans.


Did you know that not all vitamins are essential for the life of animals, as some of them are able to produce them independently? This is the case, for example, with vitamin C which is not essential for cows.

We also reiterate that some vitamins - such as vitamin A, vitamin D, vitamin PP or niacin and vitamin B9 or folic acid - derive from other substances called provitamins. These are transformed into their active form by the organism itself following their ingestion.

For further information: Provitamins: what and what they are

Types and Classification

What Vitamins Are Currently Known And How Are They Classified?

As mentioned, there are 13 vitamins currently known.

They differ in their chemical structure, functions and properties, but they certainly all play fundamental roles within the organism.

Given the heterogeneity of structure and functions, vitamins are classified into two macro-groups: that of water-soluble vitamins and that of vitamine liposolubili. Naturally, a similar subdivision derives from their different degree of solubility in fats (fat-soluble vitamins) and in water (water-soluble vitamins).

Fat-soluble vitamins

They belong to this group:

  • Vitamin A is retinolo;
  • The vitamina D o calciferolo;
  • La vitamin E, tocopherol;
  • Vitamin K.

Water-soluble vitamins

Instead, they belong to this group:

  • Vitamins of group B:
    • Vitamin B1 or thiamine;
    • Vitamin B2 or riboflavin;
    • Vitamin B3 or PP and niacin;
    • Vitamin B5 or pantothenic acid;
    • Vitamin B6 or Pyridosine;
    • Vitamin B8 or H or biotin;
    • Vitamin B9 or folic acid;
    • Vitamin B12 or Cobalamin.
  • Vitamin C or ascorbic acid.
For further information: Fat-soluble vitamins Water-soluble vitamins


What are the functions of vitamins?

Vitamins perform a wide range of functions within the body, all of which are essential for its proper functioning. In fact, they are involved in numerous reactions and metabolic processes and can contribute to the development and correct functioning of tissues and organs. Furthermore, some of them have important antioxidant properties, very important to counteract the action of free radicals (to learn more, read the article Antioxidant Vitamins).

Vitamins do not have a calorific value and do not have a purely energetic role; however they are essential for regulating a good part of the chemical reactions that take place in the body, including the energetic ones. This is the case, for example, of the B vitamins, involved in glycolysis and the Krebs cycle, two of the most important pathways for energy production.

Vitamins act as real organic catalysts with bio-regulatory functions. They therefore act as coenzymes, that is, in support of the action of enzymes to catalyze the chemical reactions necessary for life.

and Other types of vitamins, on the other hand, intervene in hormonal regulation, in the growth of bones, teeth and hair (read the dedicated article Vitamins and Hair); while others are essential for the proper functioning of the nervous system and eyes (see also the article Vitamins and Eye Health).

To learn more, read also: Functions of Vitamins, Vitamin by Vitamin

Need, Deficiency and Excess

How many vitamins does the body need?

Given the enormous importance of vitamins, it is at least clear how important it is to have the quantities necessary to meet the needs of the body.

As previously mentioned, although our body is able to synthesize a part of some types of vitamins, these micronutrients must necessarily be introduced with food.

The requirement of a given vitamin can be expressed using different indices and can vary according to the sex, age and condition in which a particular person finds himself. To find out the needs of each vitamin, consult the dedicated chapters:

  • Vitamin A requirement
  • Vitamin B1 requirement
  • Vitamin B2 requirement
  • Need Vitamin B3 or PP
  • Vitamin B5 requirement
  • Vitamin B6 requirement
  • Need Vitamin B8 or H
  • Vitamin B9 requirement
  • Vitamin B12 requirement (cobalamin)
  • Vitamin C requirement
  • Vitamin D requirement
  • Vitamin E requirement
  • Vitamin K requirement


Vitamin deficiency can lead to more or less serious consequences, depending on the extent of the deficiency, up to the onset of real diseases. Examples of diseases caused by vitamin deficiency are scurvy (vitamin C deficiency), Beri Beri (vitamin B1 deficiency), pellagra (vitamin B3 or PP deficiency) and pernicious enemia (vitamin B12 deficiency).

Vitamin deficiencies are defined as states of malnutrition in which there is not a sufficient supply of these micronutrients. The deficiency can concern only one type of vitamin or multiple: in these cases, we speak, respectively, of monovitamin deficiency or multivitamin deficiency.

For further information: Vitamin deficiency

Although in many cases the cause of vitamin deficiencies is identifiable in an unbalanced diet low in foods rich in these nutrients, it should be noted that, sometimes, such a condition can also be caused by some pathologies or by taking some types of drugs. .

For more information: Drugs that Cause Vitamin and Mineral Deficiencies


When the intake of vitamins is not sufficient to meet the needs of the body, it could be useful to resort tointegration with specific food supplements, monovitamins or multivitamins, as appropriate. It should be noted, however, that although products of this type can be freely purchased almost anywhere, they should only be used if actually needed. Also, it would be wise to ask for the preventive advice from your doctor, even more so if you suffer from particular ailments or diseases, if you are taking drugs or other products of any kind and / or if you are in "particular" conditions (for example, pregnancy, breastfeeding, etc.). In such situations, in fact, the use of vitamin supplements may be contraindicated or may require particular caution.

For further information: Multivitamin Vitamin Supplements


While the lack of vitamins can have serious consequences on health, on the other hand it is also true that the consequences can be serious and dangerous even in the case of an excess of these nutrients. Hypervitaminosis, in fact, can lead to real phenomena of toxicity.

For further information: Vitamins: Deficiency and Overdosing
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