Vitamin A, also known as retinol, is a polyisoprenoid compound that contains a cyclohexyl ring. This vitamin is stored in the liver as retinol ester.
Retinal, retinaldehyde, and retinoic acid are the three primary forms of vitamin A. Retinoic acid is involved in cellular growth and differentiation, adult organ regeneration, and regulating surfactant synthesis in the lungs.
Retinal is found in the structure of rhodopsin, which is a visual pigment. A derivative of vitamin A, called 11-cis-retinal, is present in the structure of rhodopsin. When light hits rhodopsin, it breaks into opsin and retinal, forming an all-trans-retinal. This triggers a message sent to the visual center in the brain’s posterior region.
Vitamin A also plays a role in defending against infections, which is why it is referred to as an anti-infective vitamin. Vitamin A is also an antioxidant and helps trap free radicals in tissues under low oxygen pressures.
Vitamin A Deficiency Symptoms
The first sign of vitamin A deficiency is night blindness. When the liver’s stores of retinol are depleted, night blindness occurs. Continued lack of vitamin A leads to the keratinization of epithelial tissues in the eyes, respiratory system, urinary-reproductive system, and digestive system. Drying of the mucous membranes of the eyes can eventually lead to blindness.
| Symptom or Sign | Description |
|---|---|
| Vision trouble | Night blindness, Bitot’s spots, corneal drying and clouding |
| Skin | Dry and inflamed skin |
| Immune system | Increased infections |
| Reproductive system | Difficulty conceiving |
| Other | Thinning and ulceration of the cornea, oval, triangular, or irregular foamy patches on the white of the eye, dry hair, pruritis |
