Vitamin A has been shown to play a distinct role in the development of normal epithelial cells ever since seminal work in 1925 demonstrated that lack of vitamin A in laboratory rats would result in cutaneous hyperkeratosis as well as mucosal hyperplasia and metaplasia. Vitamin A is now recognized to be essential for maintaining epithelial and mucosal surfaces, good vision, adequate hematopoiesis, and immunocompetence.
The activity or lack of vitamin A has been known from ancient Egyptian times (3500 BCE), when “roasted ox liver, pressed, applied (to the eye)” was shown to be effective in eliminating “sharew,” which was probably night blindness. Seventh-century Chinese physicians recommended the use of pig's liver to alleviate this condition. Fast-forward to the 19th century when an Austrian naval physician, Eduard Schwarz, proved that boiled ox liver was effective in treating hemeralopia, better known as night blindness.1
Parish LC. Retinoids and Carotenoids in Dermatology. JAMA. 2008;299(13):1611-1612. doi:10.1001/jama.299.13.1611