What is the relationship between vitamin A and vision?
Vitamin A is a fat soluble vitamin with A1 A2 two types. A1 is retinol, A2 is 3-dehydroretinol, with only half the activity of the former. It can be used for Cosmetic Raw Materials. Narrowly defined, vitamin A refers to vitamin A1, while broadly defined, vitamin A refers to various compounds with similar structures that can be converted into vitamin A, including retinol, retinol esters, and some carotenoids. Widely used in Anti Aging Raw materials, cosmetics & personal care industry.
Vitamin A is related to vision. The rod cells in the human retina contain rhodopsin, a G protein coupled receptor (GPCR) involved in dark vision processes. Vitamin A is converted to retinol under the action of alcohol dehydrogenase, and 11 cis retinol binds to the lysine amino group on retinoin to form rhodopsin.
Under light irradiation, 11 cis retinol in rhodopsin isomerizes into all trans retinol, causing a series of conformational changes in the visual protein, activating the coupled G protein, producing the cyclic guanosine monophosphate (cGMP) second messenger. Through cascading amplification, it forms an optic nerve impulse and generates visual signals in the brain. The research on rhodopsin and vision was awarded the Nobel Prize in Physiology and Medicine in 1967.
During the photosensitivity process, rhodopsin will decompose and then recombine in the dark, forming a visual cycle. This process takes about 30 minutes and is called dark adaptation. If vitamin A is insufficient, it can lead to slow regeneration of rhodopsin, prolonged dark adaptation time, and even dark vision disorders, namely night blindness. Supplementing with vitamin A can be therapeutic. In addition to dark vision, photopsin, which is responsible for color perception in cone cells, also contains retinol. However, there are three types of corresponding cone proteins responsible for sensing light of different wavelengths.
Vitamin A deficiency can also lead to dry eye syndrome. Firstly, the tear gland and mucus secreting epithelium are replaced by keratinized epithelium, causing conjunctival dryness. Subsequently, keratin fragments accumulate and form small opaque plaques (Bitot spots), ultimately leading to complete blindness due to corneal softening and destruction. So vitamin A, also known as anti dry eye alcohol.
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