Provitamin A

Definition

Vitamin A can be found in natural state in two forms:

-provitamin A, in some vegetables, that the liver turns (by oxidation) into vitamin A depending on its needs in order to be used by the body. With this designation of “provitamin A” are grouped different molecules (in particular alpha and beta carotene) that the body used in order to produce vitamin A.

-vitamin A or retinol which is its “free” form, only in animal foods.

So, provitamin A is the precursor of vitamin A and retinol is the active form of vitamin A, directly assimilated by the body. Beta carotene is the most powerful precursor of vitamin A.

Roles in the body

The precursors of vitamin A (that is to say “provitamin A”) have effects similar to the vitamin itself. That is a large family of vegetable molecules, which often brings colours: lutein, zeaxanthin, lycopen, and carotene…are also named “vitaminic pigments”.

Provitamin A is an antioxidant defending against some diseases by the override of free radicals (unstable oxygen molecules) that we can find in the body. This antioxidant property reduces cancer risks by, in particular, the prevention of bladder, mouth, larynx, lungs, breast, oesophagus and probably colon tumours.

Provitamin A also permits the synthesis of eye pigments and prevents different eyesight disorders. It improves at the same time the nocturnal vision.

Moreover, it has beneficial effects on immune system, reducing the risks of infections.

It also intervenes on wound healing process and protects the skin against outer attacks such as sun.

At last, provitamin A protects cerebral cells from damages linked to the age and reduces heart attack risks and cerebrovascular accidents.

Sources in vegetables and some others food products(Ciqual data *)

Provitamin A is exclusively in vegetable lineage foods, but also in eggs and butter.

Food products' contents in provitamin A	mg / 100g*
Sorrel	11
Turnip	7
Chervil	6.2
Carrot	6
Dandelion	6
Spinach	5.5
Parsley	5
Apricot	4
Nectarine	2
Egg yolk	2
Escarole	2
Chicory	1.8
Red cabbage	1.5
Dried peach	1.2
Lettuce	1
Whole egg	0.6
Butter	0.5

Recommended intakes

Vegetables organisms can cover the total needs in vitamin A.

The recommended daily intake (RDI) is from 3 to 5 mg.

It is evaluated that 800 µg of vitamin A is equivalent to 4,800 µg of provitamin A.

The Advised Nutritional Intakes in vitamin A are given for French population according to ages.

Ages	Advised Nutritional intakes in vitamin A (µg a day)
Infants	350
Children 1-3 years	400
Children 4-6 years	450
Children 7-9 years	500
Children 10-12 years	550
13-15 years (boys)	700
13-15 years (girls)	600
16-19 years(boys)	800
16-19 years (girls)	600
Adults (men)	800
Adults (women)	600
> 75 years	600 - 700
Pregnant women	700
Breast-feeding women	950

Deficiences and excesses

A heavy deficiency can lead to an irreversible blindness. If the deficiency persists, it can even become fatal. Generally, a deficiency in vitamin A manifests itself by a white and dried skin, a nocturnal view decline, the appearance of conjunctivitis, hypersensitivity to infections, growth decline and reproduction disorders.

Some persons can have deficiency risk in vitamin A: pregnant women, people who consume regularly tobacco or alcohol, old people, diabetics, people with cancers, HIV positive persons, persons often exposed to the sun and people sensitive to allergic skin disorders.

Contrary to vitamin A, an excess of precursors doesn’t lead to toxicity but only to a yellow reversible and without danger coloration of the skin. Provitamin A turns into vitamin A only contingent to the needs of the body. In addition, as its absorption by the body is small, it doesn’t exist excessive dose risks.

An excess of vitamin A can become poisonous when the ingestion of this micronutrient overtakes 50,000 UI a day that is to say around 10 times the RDI and for months.

This quantity is very important, and his kind of excess is rare. However, an occasional excess below 50,000 UI a day is more common and can cause diverse and different symptoms such as nausea, vomiting, vision disorders, headaches, capillary loss, the drying of the skin, pains in articulations, a bony weakness as well as a liver enlargement due to a too huge storage in this organ.

It is important to keep in mind, as it had been said previously, that the conversion of provitamin A to vitamin A takes place only according to the needs of the body and so it can’t lead to any excess of vitamin A. Only, too important intakes of animal origin products, or dietary supplements badly measured, and/or medicines rich in vitamin A can explain these high quantities in the body.

Weak points

Vitamin A is a liposoluble vitamin, heat-, acid- and base- resistant, but easily oxidized, that is to say, very liable to deteriorate by the air and rapidly destroyed by the light.

Cleverness and advices of the nutritionist

One handful of spinach leaves, one carrot juice or some apricots: one of these foods, once a day, brings fully our daily need in provitamin A.

When you prepare vegetables rich in provitamin A, like carrot, always use a bit of oil. This oil will improve the assimilation of this liposoluble provitamin.