Vitamin A

What is Vitamin A?

Vitamin A and its metabolites play diverse roles in physiology, ranging from incorporation into vision pigments to controlling transcription of a host of important genes. Health depends on maintaining vitamin A levels within a normal range, as either too little or too much of this vitamin lead to serious disease.

Vitamin A deficiency

• Blindness due to inability to synthesize adequate quantities of rhodopsin. Moderate deficiency leads to deficits in vision under conditions of low light ("night blindness"), while severe deficiency can result in severe dryness and opacity of the cornea (xeropthalmia)
• Increased risk of mortality from infectious disease has been best studied in malnourished children, but also is seen in animals. In such cases, supplementation with vitamin A has been shown to substantially reduce mortality from diseases such as measles and gastrointestinal infections.
• Abnormal function of many epithelial cells, manifest by such diverse conditions as dry, scaly skin, inadequate secretion from mucosal surfaces, infertility, decreased synthesis of thyroid hormones and elevated cerebrospinal fluid pressure due to inadequate absorption in meninges.
• Abnormal bone growth in vitamin A-deficient animals can result in malformations and, when the skull is affected, disorders of the central nervous system and optic nerve.

How do I find out more?