Hello everyone,
welcome to my blog, today i want us to look at the contributions of Vitamin A to vision and the bad things that can happen to our eyes when we fail to take have sufficient amount in our system.
Introduction
Vitamins are chemical substances, similar to the nutrients we gain from eating. And they does a lot of good for the body in addition to protecting the our systems from diseases and invasion of microbes by strengthening our immune system and enhancing function of organs in our body. Their inadequacies brings about deficiencies and their excess can also pose a health threat to our system, hence there is the need to find the balance.
Vitamins are organic in nature and thus are easily destroyed by nature in the form of light, heat and oxygen. Water soluble vitamins including vitamin C and B are easily dissolved in water whereas the lipid soluble vitamins inlcuding A, D, E and K are dissolved in lipid or oil.
Vitamin A
The vitamin A is a fat soluble vitamin that dissolves in lipid. It come in three forms thus retinal, retinol and retinoic acid and may be found in food and nutritional supplements. Another form of vitamin A which is known as the carotenoids is mostly obtains from plants and although it is not as efficient as the others it does similar functions and a lot of good for the body.
Each of the three forms of has different roles they perform in the body because of which the body may convert from one form to another. Retinol can be converted to retinal and into retinoic acid. Retinol is mainly involved in reproductive health, retinoic acid regulates growth whiles retinal is mostly involved in vision.
Rhodopsin
The retinal has photoreceptors that undergoes phototransduction to convert light energy into electrical impulses. Receptors for color vision are known as cones whereas those for monochromatic vision are the rods. In these receptors are what we call pigments which are the ones mainly involved in the phototransduction process. The Rods form the greater majority of the retina and the pigment responsible for is what we call rhodopsin.
Vitamin A is present in rhodopsin in the form of retinal and forms a bond with protein (rhodopsin.) Their bond allows detachment in the present of light initiate the phototransduction process which involves some isomerization and deprotonation. Thus in the absence of vitamin A phototransduction would be hindered and so when it is in inadequate amounts it results in a condition known as nyctalopia or night blindness.
Functions of Vitamin A
The most common and important function known to us is its contribution to vision as already explained. Then it also maintains the integrity and of the cornea and other epithelial membranes in the eye, the carotenoid forms have anti-oxidation effect and it also helps in strengthening the immune system and your reproductive health.
Sources of Vitamin A
Excellent sources of vitamin A include Beef liver, Sweet Potatoes and Mangoes. Some other good sources include Broccoli, Carrots, water melon, eggs and Tomato Juice.
Vitamin A Deficiency
Inadequate amounts of vitamin A in the system could result in night blindness as already mentioned, dry corneal since it helps in maintaining its integrity, impaired immunity, macular degeneration and xerophthalmia (drying of the conjunctiva).
There is hardly an issue of toxicity from too much intake since the system is able to regulate by converting to other forms however to be on the safer side it is recommend that one sticks to the recommended daily allowance as per the FDA in their country.
References
Robert B. Rucker, John W. Suttie, Donald B. McCormick. (2001) Handbook of Vitamins. 3rd Edition. New York. Marcel Derker, Inc.
ANTOINETTE PIRIE, Ph.D., VITAMIN DEFICIENCY AND VISION, British Medical Bulletin, Volume 12, Issue 1, January 1956, Pages 32–34, https://doi.org/10.1093/oxfordjournals.bmb.a069510
Rando, R.R. (1990), The Chemistry of Vitamin A and Vision. Angew. Chem. Int. Ed. Engl., 29: 461-480. doi:10.1002/anie.199004611
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I remember reading somewhere, can't remember exactly where, that Retinol has a role in the coloring of the iris with melanin, is this true?
The color of the iris is mainly determined by the amount of melanin and i do not recall ever coming across retinol playing any such role, the more the melanin the browner the iris color but i would read more into this and let you know, Thanks for reading