Vitamin A has a vital role in vision.
It is also known as
retinol. The retina is the light-sensitive layer at the back of the eye, and the rods and cone cells found here all use a derivative of retinol -
retinal, in conjunction with other compounds.
Vitamin A in the body can come from several dietary sources: esters, e.g. retinyl palmitate, which are simply hydrolysed in the digestive system, or via related carotenoid compounds, e.g. carotene, which require more processing.
The retinol molecule consists of a
ring section with a
side chain containing four double bonds, and with an
-OH (
alcohol) group at the end. This molecular structure - empirical formula
C20H30O - explains why retinol is fat soluble.
Another way of describing retinol is "(
2E,
4E,
6E,
8E)-
3,7-Dimethyl-9-(
2,6,6-trimethyl-1-
cyclohexen-1-yl)-
2,4,6,8-nonatetraen-1-ol".