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Vitamin A is one of the 4 fat soluble vitamins along with vitamin D, Vitamin E and Vitamin K. It is multifunctional and essential which means that it is not produced by the body. In this article we will touch on aspects of Vitamin A absorption and it’s effect on wound healing as well as its metabolism.
We often think of Vitamin A as the critical vitamin for vision, however it has several other roles that related to immune function, protein synthesis, and cellular communication. Vitamin A deficiency is a concern world wide because of the natural of the side effects. Vitamin A deficiency is the leading cause of preventable childhood blindness in the world according to UNICEF and sometimes it may be undetected until there is irreversible damage.
There are 2 chemical forms of vitamin A in diet:
Retinoids (Preformed vitamin A) This group include retinol, retinyl esters, and retinal they are mostly found in animal sources like liver, egg yolk or fish oils.
Carotenoids (Provitamin A) This group includes beta-carotene, alpha-carotene and lycopene, mainly found in plant sources like leafy vegetables or yellow/orange vegetables and fruits.
The Physiology of the Vitamin A is as follows:
1.- Ingested food is digested in the stomach where retinyl palmitates (esters) are released from proteins. Retinol and beta-carotene are absorbed directly into the small intestine where retinyl esters and betacarotene are transformed into retinol . Retinol is the most easily absorbed form of vitamin A.
2.-That retinol absorbed by the enterocytes in the ileum (small intestine) along with bile is then transported to the liver with the help of chylomicrons a protein that transports fat.
3.-Fifty to 80% of the vitamin A is stored in the liver and the remaining is deposited into adipose tissue, lungs and kidneys.
4.-When stored retinol is released from the liver into the circulation to target organs, it is bound to plasma retinol-binding protein (RBP4) a transporting protein produced by the liver that requires ZINC, which is synthesized by the liver; This complex is stabilized by transthyretin (TTR), which reduces renal excretion.
Retinol is a crucial component for reproduction, embryological development, cellular differentiation, growth, protein synthesis, and immunity in the form of retinoic acid and vision in the form of retinal.
One of Vitamin A additional roles is in epithelial health of skin and mucous membranes. It increases epithelial turnover which is crucial during would healing. It also has anti-oxidative effects which prevent cell damage and can prevent or reverse the effects of other damaging agents. In addition to these benefits it has also been associated with increasing collagen, fibronectin, keratinocytes and fibroblast, all important in wound tissue structure. There have been some studies that suggest giving higher doses of Vitamin A in patients with non or slow healing wounds.
It is important to remember that we have documents delayed diagnosis of adult vitamin A deficiency leading to significant night blindness in adults. It is critical that the patients and their primary care physicians are acutely aware of this possibility. In majority of the patients with low vitamin A, post weight loss surgery, aggressive supplementations, including injections need to be considered as a part of the treatment regimen.
We would like to thank Miguel Rosado, MD for his significant contribution provided for this Blog.
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