Vitamin+A--Carolyn+and+Heather



Vitamin A originates in animal sources (dairy products, fish, and meat) as retinol, retinal, and retinoic acid (also known as preformed vitamin A) (D/D pg. 283). Vitamin A is also found in plant sources as carotenoids (precursors to vitamin A), including beta-carotene (D/D pg. 283). Two forms of vitamin A are available in the human diet, preformed vitamin A and provitamin A carotenoids (National Institutes of Health). Preformed vitamin A is found in food products, those which are listed above and provitamin A carotenoids can be found in plants such as dark leafy vegetables such as spinach (D/D page 283). Vitamin A is not banned by the NCAA or the IOC.

Vitamin A can be purchased online or in any store that sells vitamins (drug store, grocery store, Walmart, Target) in pill form or liquid drops for under $20.00. Vitamin A can be found naturally in the following:
 * **Animal (preformed vitamin A):** liver, fish, oil, milk, milk products (fortified) (D/D pg. 283).
 * **Plant (provitamin A):** dark-green leafy vegetables (ex: spinach), orange fruits, vegetables (ex: carrots, cantaloupe, tomatoes)(D/D pg. 283).



For thousands of years vitamin A's contribution to vision has been recognized and was even known by the ancient Egyptians who would use raw liver (highest source of Vitamin A) for eye disease (Vitamin A From Physiology to Disease Prevention). The New England Journal of Medicine conducted an experiment on vitamin A to test the theory that carotenoids and retinoids in vitamin A are agents that may help prevent lung cancer and cardiovascular disease, which is the leading cause of death in the United States.Results showed that after four years of supplementaion vitamin A had no benefit and and may have even had an unfavorable effect on the result of lung cancer and the risk of death from cardiovascular disease.

Another study was done on vitamin A and the relativity it had with mortality rate with children worldwide. The study took place in Southern India where vitamin A deficiency and under nutrition are documented. After a year results had shown that the risk of death in the group that received vitamin A was less than half of the control group which did not receive the vitamin. Vitamin A contributed substantially to the survival of the children and reduced mortality rate by fifty four percent. A study was conducted by reviewing the effects of supplementing vitamin A during pregnancy (McCauley et al. 2015). The study found that vitamin A does not affect the risk of maternal mortality confidence intervals, perinatal mortality, neonatal mortality, stillbirth, neonatal anemia, preterm birth, or the risk of having a low birth-weight baby (McCauley et al. 2015). Vitamin A supplementation reduces the risk of maternal night blindness, and also may reduce maternal clinical infection, and maternal anemia (McCauley et al., 2015). Vitamin A is a fat soluble vitamin that acts as an antioxidant, antioxidants are chemicals that may reduce the risk of someone getting cancer. These vitamins are stored in the liver and get sent out to other organs when needed. Vitamin A is important to the growth of bones as well as vision, for example night vision is very dependent on vitamin A. Vitamin A aids in forming pigments in our eyes to help our eyes adjust to light, it also plays a role in the production of white blood cells which is important for fighting off viruses and bacteria. Mechanisms involved in the digestion and absorption of dietary vitamin A require the participation of several proteins (Harrison, 2005). Dietary retinyl esters are hydrolyzed in the intestine by the pancreatic enzyme, pancreatic triglyceride lipase, and intestinal brush border enzyme, phospholipase B (Harrison, 2005). Unesterified retinol taken up by the enterocyte is complexed with cellular retinol-binding protein type 2 and the complex serves as a substrate for reesterification of the retinol by the enzyme lecithin:retinol acyltransferase (LRAT) (Harrison 2005). The retinyl esters are then incorporated into chylomicrons, intestinal lipoproteins containing other dietary lipids, such as triglycerides, phospholipids, and free and esterified cholesterol, and apolipoprotein B (Harrison, 2005). Chylomicrons containing newly absorbed retinyl esters are then secreted into the lymph (Harrison, 2005). Although under normal dietary conditions much of the dietary vitamin A is absorbed via the chylomicron/lymphatic route, it is also clear that under some circumstances there is substantial absorption of unesterified retinol via the portal route (Harrison, 2005). Evidence supports the idea that the cellular uptake and efflux of unesterified retinol by enterocytes is mediated by lipid transporters, but the exact number, identity, and role of these proteins is not known and is an active area of research (Harrison, 2005). __References__ Bennasir, H., Sridhar, S., Tech, M., & Abdel-Razek, T. (2010, March). Vitamin A from Physiology to Disease Prevention. Retrieved from http://www.globalresearchonline.net/volume1issue1/Article%20014.pdf Dunford, M., & Doyle, J.A. (2015) //Nutrition for Sport and Exercise// (3rd ed.). CT: Cengage Learning. Harrison, E. H.(2005) MECHANISMS OF DIGESTION AND ABSORPTION OF DIETARY VITAMIN A*. //Annu. Rev. Nutr.,//25,87-103

Omenn, G. S., Goodman, G. E., Thornquist, M. D., Balmes, J., Cullen, M. R., Glass, A.,. . . Keough, J. P. (1996, May 2). Effects of a Combination of Beta Carotene and Vitamin A on Lung Cancer and Cardiovascular Disease — NEJM. Retrieved from http://www.nejm.org/doi/full/10.1056/nejm199605023341802 Underwood, B. A., Rahmathullah, L., Thulasiraj, R., Milton, R. C., Ramaswamy, K., Rahmathullah, R., & Babu, G. (1990, October 4). Reduced Mortality among Children in Southern India Receiving a Small Weekly Dose of Vitamin A — NEJM. Retrieved from http://www.nejm.org/doi/full/10.1056/NEJM199010043231401 Van Den Broek, ., Dou, L., Othman, M., Neilson, J.P., Gates, S., & Guelmezoglu, A. M. (2010). Vitamin A supplementation during pregnancy for maternal and newborn outcomes. //The Cochrane Library.// Vitamin A Nutrition Facts - MyFoodDiary. (n.d.). Retrieved from http://www.myfooddiary.com/Resources/nutrient_facts/nutrient_vitaminA.asp Vitamin A — Health Professional Fact Sheet. (2013, June 5). Retrieved from https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/