Vitamin A is a fat soluble vitamin. Retinol, retinal, and retinoic acid (RA) are the different forms of vitamin A (1). It plays a role in maintaining vision, promoting growth and development of epithelium and mucus integrity. Vitamin A helps to enhance immune health with the help of its anti-inflammatory properties. It is reported to play protective role against measles & respiratory tract infection (1).

Carotenoids which contains at least 1 unsubstituted β-ionone ring can potentially yield vitamin A due to which it is called as provitamin A carotenoids. Human diet contains more or less 50 carotenoids out of which only 5 or 6 are detectable in human plasma & they are α- and β-carotene, β-cryptoxanthin, lycopene, lutein, zeaxanthin. Because of its structure and cleavage efficacy only α- and β-carotene and β-cryptoxanthin have provitamin A activity. Among all of these carotenoids, all-trans-β-carotene is the most suitable precursor for vitamin A (3).

Toxicity issues are associate with an excess intake of Vitamin A. But the toxicity of Vitamin A does not occur with the high doses of β-carotene. It is because of the cleavage of β-carotene which is regulated through feedback mechanisms, only desired and necessary amount of Beta carotene gets metabolized to retinol. Therefore it is recommended to consume dietary requirement of Vitamin A in the form of Beta carotene (3).

Vitamin A and epithelial tissue function

• Vitamin A helps in the morphological formation of epithelial tissue which includes epithelial keratinization, stratification, differentiation, and functional maturation of epithelial cells. It is an integral part of the mucus layer present in the respiratory tract and the intestine. It improves the antigen non-specific immunity as it is involved in mucin secretion (1).

Immune health

• Vitamin A is involved in the development of the immune system and plays regulatory roles in cellular immune responses and humoral immune processes (2).
• Helps maintain structural and functional integrity of mucosal cells in innate barriers (e.g., skin, respiratory tract, etc.) (2)
• It is important for normal functioning of innate immune cells (e.g., NK cells, macrophages, neutrophils) (2).
• Necessary for proper functioning of T and B lymphocytes and thus for generation of antibody responses to antigen (2).
• Involved in development and differentiation of Th1 and Th2 cells and supports Th2 anti-inflammatory response (2).
• Another function of vitamin A, suggests that it provides protection against infections (2).

Eye health

• In the eye vitamin A has a specific, highly complex function in dark vision (4).
• Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea (4).
• Vitamin A deficiency leads to night blindness (4).

Beta carotene and skin health

• several studies on Beta carotene have reported a protective effects of beta carotene against acute and chronic skin photodamage. It protects the skin form UV-induced erythema (3).