Vitamin A is essential at all stages of life. It is involved in a number of bodily functions, particularly eyesight. Below you will find information on its role, the foods in which it can be found, recommended intake levels for the various categories of the population, and disorders associated with inadequate intakes.
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Updated on 04/08/2016
Vitamin A & provitamin carotenoids
Presentation, food sources and nutritional needs
Definition, functions and roles
Any natural compound presenting similar biological characteristics to retinol is called vitamin A. Retinol is the main precursor of the active vitamin A molecule. In humans and most animal species, it can also be formed from certain carotenoids (plant pigments), mainly ß-carotene. Preformed vitamin A and vitamin A provided by the conversion of carotenoids constitute the total vitamin A intake.
The vitamin A activity of these compounds is expressed in relation to the retinol activity according to a retinol equivalent (RE) system; in humans, 6 mg of ß-carotene have the same activity as 1 mg of retinol. Note that the term "retinoids", referring to both natural and synthetic compounds (medicinal products), is not used in the food context.
Vitamin A is essential at all stages of life. Its key role in the mechanism of eyesight is now clearly established. It also plays a part in the regulation (activation, repression) of gene expression, and is thus involved in a number of bodily functions: development of the embryo, cell growth, tissue renewal (skin, intestinal mucosa), immune system, etc.
In addition to the properties of vitamin A, ß-carotene can act as an antioxidant
Foods that are rich in vitamin A and sensitivity of the vitamin
In food, vitamin A is present in the form of retinol and its derivatives exclusively in products of animal origin, while in the form of provitamin carotenoids it is mainly found in products of plant origin.
The livers of fish and farmed animals are richest in retinol. In contrast, vegetables are richest in ß-carotene: sweet potato, carrot, pumpkin, dandelion, mixed vegetables, parsley and other herbs, lettuce, spinach, etc.
The lists of foods that are rich in retinol and b-carotene may be consulted on the table Ciqual :
ß-carotene may lose its activity: during storage (due to the effects of light, oxygen and enzymes) and during dehydration of food. In contrast, freezing preserves its activity. Vitamin A may lose its activity and be destroyed by air oxidation (rancidity), especially in the presence of light and heat. However, it remains fairly stable during cooking (maximum loss of about 15%).
French population reference intake (PRI)
Reference intakes (PRI) are proposed to cover the “normal” needs of the French population.
The reference intakes in vitamin A are 800 µg RE per day for adult men, and 600 µg RE for adult women. For children, ANCs range from 450 to 550 µg RE according to age.
It is traditionally recommended that around 60% of intake come in the form of carotenoids.
Levels and sources of intake
The average intake of retinol in the French population (INCA2 2006-07 data) is 445 µg/day for children aged 3 to 17, and 702 µg/day for adults over the age of 18. These intakes are higher for the male population, both in children and adults. The average intake of ß-carotene is 3335 µg/day for adults and 2076 µg/day for children.
The main intake sources of retinol in the French population are offal and delicatessen meats which contribute respectively 15% and 19% of intake in children, and respectively 29% and 20% of intake in adults. The main intake sources of ß-carotene are vegetables which contribute 60% in adults and children, as well as soup.
Risks of deficiency and excess intake
A reduction in visual acuity, especially in twilight glow (nocturnal vision), is one of the first visible signs of vitamin A deficiency in humans. Vitamin A deficiency does not seem to exist in industrialised countries, unlike the major public health problems that it poses in developing countries. However, in vulnerable groups (children and the elderly), the consequences of a moderate vitamin A deficiency, particularly due to infectious states, can be of concern.
Great caution is advised for women who are pregnant or who wish to become pregnant because excess vitamin A is associated with birth defects. Pregnant women should not eat liver regularly because this foodcontains large quantities of vitamin A that can be directly assimilated. On the other hand, food intakes of provitamin A (colourful fruits and vegetables) are safe, even during pregnancy.
High intakes (greater than 1500 µg RE per day) increase the risk of fractures in post-menopausal women.