This isn’t an easy topic to write about nor is it an easy topic to find information about since it’s quite complex.
Contents
Function
Dations for vitamin A, as well as other nutrients, are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine. An RDA is an intake level based on scientific research evidence. It is set at a level that is thought to ensure enough nutrition.
Dietary reference intakes for vitamin A:
Infants (AI)
0 to 6 months: 400 micrograms per day (mcg/day)
7 to 12 months: 500 mcg/day
The Recommended Dietary Allowance (RDA) for vitamins is how much of each vitamin most people should get each day.
Vitamin A Deficiency
Deficiency of vitamin A results in various disorders that most commonly involve the eye and the epithelial tissues. This aspect of vision is normally dependent on rhodopsin, which maintains its photosensitivity only in the presence of vitamin A.
In xerophthalmia, the eyes are sensitive to light, the secretion of lubricating tears is stopped, and the eyelids become swollen and sticky with pus. This condition will eventually result in blindness. Except in the later stages, when cellular damage in the cornea and associated deeper structures is too extensive, xerophthalmia can be effectively treated with vitamin A.
Although xerophthalmia is seldom encountered in countries where dairy products are readily available, it is common among poor children in Indonesia, Bangladesh, India, and the Philippines, and occurs in some parts of Africa. If insufficient intake of vitamin A is prolonged, the skin may become dry and rough, with the appearance of plugs of horny material about the hair follicles (follicular hyperkeratosis).
Vitamin A Excess
Vitamin A excess, also called hypervitaminosis A, is a toxic condition produced by a high intake of vitamin A, generally 150,000 μg daily over a period of several months.
Vitamin A and vitamin A derivatives, such as the acne medication isotretinoin, can cause birth defects when taken in excess during pregnancy.