Vitamin A (retinol) is a fat-soluble vitamin essential for vision, growth, reproduction, cell division, and the
integrity of the immune system.
The most well-known function of vitamin A is its role in vision. As part of the membrane-bound visual protein
rhodopsin, vitamin A is essential in the eyes for converting light into nerve impulses. Night blindness and
xeropthalmia are signs of moderate to severe vitamin A deficiency. Xerophthalmia is a common cause of
preventable blindness in many underdeveloped countries around the world.
Vitamin A is essential for normal cellular differentiation. Its metabolite, retinoic acid, assumes a central role in
gene activation and transcription. As a result, vitamin A status has profound effects on all rapidly dividing
tissues in the body, such as immune cells and intestinal cells, and affects fertility, fetal development and
Cellular differentiation is crucial for normal immune response, and vitamin A deficiency can start a vicious cycle
affecting the immune system. During vitamin A deficiency, immune function is impaired, which puts the body
at increased risk for infections. Acute infections further deplete the body of vitamin A, which leads to an even
more impaired immune function and an even lower resistance to infections.
While a few studies have found that vitamin A status in developed populations may be adequate, many studies
showed that marginal vitamin A deficiency is quite common. Women often have lower vitamin A levels than
men – who tend to consume more meats high in vitamin A. The elderly and immune-compromised are also at
increased risk for marginal vitamin A deficiency. The intestinal absorption of vitamin A is associated with fat
absorption. Therefore, some dietary fat must be present for efficient vitamin A absorption to occur.