Vitamin A is a group of fat-soluble compounds that can be differentiated into two categories, depending on whether the food source is an animal or a plant:

 

• Vitamin A found in foods that come from animals is called ’preformed vitamin A’ or ’retinol’; it is one of the most active forms of vitamin A.
• Vitamin A found in fruits and vegetables is called ’provitamin A carotenoid’, which can be cleaved into retinol in the body; the carotenoid ’beta-carotene’ is most efficiently converted into retinol, making it an important vitamin A .

A sufficient vitamin A (retinol) intake is essential for

 

• the process of vision (especially night vision)
• growth and development – it is involved in the genetic regulation of cell and tissue formation, programming, and communication needed for reproduction and for the proper development of the embryo in the womb
• immune function – it helps to protect against infections by ensuring the effectiveness of mechanical barriers (e.g., skin), and increasing the production and efficacy of protective cells (e.g., lymphocytes)
• male and female reproductive organs.

 

The European Food Safety Authority (EFSA), which provides scientific advice to assist policy makers, has confirmed that clear health benefits have been established for the dietary intake of vitamin A in contributing to:

 

• normal cell differentiation;
• a normal function of the immune system;
• the maintenance of normal skin and mucous membranes;
• the maintenance of normal vision;
• normal iron metabolism.

Cancer

Presently, there is only little evidence in humans that increased intake of natural (in food) or isolated vitamin A (in dietary supplements) reduce breast or lung cancer risk.

 

Eye disease

Vitamin A supplementation is successfully used to prevent deficiency-related eye diseases such as xerophthalmia, which may progress to blindness.

Please note:

Any dietary or drug treatment with high-dose micronutrients needs medical supervision.

 

Eye and skin disease

High doses of vitamin A (retinol) supplements have been used successfully to treat an inherited eye disease (retinitis pigmentosa) and the symptoms of some severe skin disorders (psoriasis and acne).

The recommended daily intake of vitamin A varies according to age, sex, risk group and other criteria applied in individual countries: 700–1000 micrograms (mcg) Retinol Equivalents (RE) per day for men, 600–800 mcg RE/day for women. In the USA the recommended intake for adults is 900 mcg (men) and 700 mcg (women) per day of preformed vitamin A (retinol).

Surveys undertaken in a number of countries suggest that vitamin A intake patterns vary considerably across Europe and in the U.S. The number of people at risk from vitamin A deficiency depends on the intake of total vitamin A, which is defined as preformed (retinol) and provitamin A (e.g. beta-carotene).

 

Based on numerous studies it is evident that parts of the world’s population do not receive the RDA for vitamin A through dietary sources for preformed vitamin A. To fill the gap between low intakes from sources containing preformed vitamin A, adequate amounts of provitamin A, such as beta-carotene, must be supplied. However, according to national nutrition surveys, beta-carotene intake, and therefore the provitamin A supply of large parts of the population, is insufficient.

Vitamin A deficiency usually results from inadequate intake of foods high in vitamin A or beta-carotene, a precursor of vitamin A. The earliest symptom of vitamin A deficiency is night blindness. Groups at risk for insufficient vitamin A supply are mainly pregnant and breast-feeding women, newborns, children with frequent infections, the elderly and people who avoid animal-derived foods.

The richest food source of preformed vitamin A is liver, with considerable amounts also found in egg yolk, whole milk, butter and cheese. Provitamin A carotenoids (e.g., beta-carotene) are found in carrots, yellow and dark green leafy vegetables (e.g., spinach, broccoli), pumpkin, apricots, melon, and palm oil.

Because vitamin A is stored in the liver, large amounts taken over a period of time can eventually exceed the liver's storage capacity and produce adverse effects, such as liver damage, bone abnormalities and joint pain.

 

Some research has associated high-dose vitamin A (retinol) supplementation over several years with an increased risk of osteoporosis and (together with other antioxidants) lung cancer. The reasons for these findings are not yet clear. However, it is difficult to interpret these effects, as experts have raised serious doubts about the conclusions reached due to invalid analysis methodology and other studies have not shown such effects.

 

Pregnancy risk

Normal foetal development requires sufficient vitamin A intake. Based on animal studies with retinoic acid it has been suggested that consumption of high doses of retinol during pregnancy may cause malformations in the newborn.

 

Tolerable upper intake level

To avoid such adverse effects, upper intake levels of preformed vitamin A have been set at 3,000 micrograms Retinol Equivalents (RE) per day for adults with appropriately lower levels for children.

 

Drug interactions

Please note:

Because of the potential for interactions, dietary supplements should not be taken with medication without first talking to an experienced healthcare provider.