What Are Vitamins Vitamins Essential nutrients that your body needs in small amounts to grow reproduce and maintain good health Travel through the cells of the intestinal wall and are packaged with fat and other lipids in chylomicrons Travel through lymph system before they enter the bloodstream Vitamins Are Either Fat Soluble or Water Soluble Fat Soluble Vitamins A D E and K Absorbed at the beginning of the small intestine They are packaged with fatty acids and bile in micelles Stored in body until needed Can be toxic in high doses Needed in small amounts cid 127 Water Soluble Vitamins B and C Absorbed with water and enter bloodstream directly Not stored in body Excess amounts are excreted Needed in small amounts Not toxic but excess can be harmful Some Vitamins Function as Antioxidants cid 127 Most are absorbed in the upper portion of the small intestine although vitamin B12 is absorbed in the lower part of the small intestine Antioxidants Substances that neutralize free radicals Vitamins A C and E and beta carotene are antioxidants cid 127 Oxidation The process during which oxygen combines with other molecules A harmful chemical reaction that takes place in cells Free Radicals Unstable oxygen containing molecules that can damage the cells of the body and possibly contribute to the increased risk of chronic diseases Can damage cell structure cell preens and even DNA Steal electrons from other molecules to stabilize themselves A chain reaction that if not stopped can be significantly damaging to cells Normal by products of the body s metabolic reactions Can result from exposure to chemicals in the environment cigarette smoke and air pollution and from the damaging effects of the sun s ultraviolet rays on unprotected skin cid 127 Oxidative Stress When free radicals accumulate faster than your body can neutralize them Can contribute to health problems including heart disease cancer type 2 diabetes arthritis and Alzheimer s disease Age related Macular Degeneration AMD A disease that affects the macula of the retina causing blurry vision A study conducted by the National Eye Institute NEI discovered that supplements containing large amounts of antioxidants vitamin C vitamin E and beta carotene with the minerals zinc and copper are effective in reducing the risk for AMD as well as the extent of vision loss Cataract A common eye disorder that occurs when the lens of the eye becomes cloudy cid 127 More than half of all Americans have experienced cataracts by the time they reach 80 years of age Many undergo surgery to remove them Phytochemicals Naturally occurring substances in fruits vegetables and whole grains that protect against certain chronic diseases Vitamins Differ in Bioavailability Bioavailability The degree to which a nutrient is absorbed from foods and used in the body For example a young child or pregnant woman will absorb more ingested vitamins than will a non pregnant adult The bioavailability of fat soluble vitamins is usually less than that of water soluble vitamins because fat soluble vitamins require bile salt and the Vitamins in plant foods are typically less bioavailable than those in animal foods because plant fiber can trap vitamins formation of a micelle to be absorbed Vitamins can be destroyed by air water or heat Don t Expose Produce to Air Vegetables and fruits begin to lose their vitamins almost immediately after being harvested Should be stored in air tight containers and prepared cut up right before use A Little Water is Enough Reduce Cooking Time Soaking foods will cause water soluble vitamins to leach out of the food and into the liquid To reduce vitamin loss only use enough water to stop the pan from scorching and vegetables from becoming crisp Prolonged heat from cooking will destroy water soluble vitamins especially vitamin C Because they are exposed to less heat vegetables cooked by microwaving steaming or stir frying can have approximately 1 5 times more vitamin C after cooking than if they were boiled Keep Your Food Cool Cooler temperatures help preserve vitamins cid 127 Overconsumption of Some Vitamins Can Be Toxic Toxicity hypervitaminosis The accumulation of a substance to the level of being poisonous Very rare condition that usually only occurs when an individual takes a megadose level of vitamin supplements Tissues become saturated cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 cid 127 The excess vitamins can damage cells sometimes permanently cid 127 Megadose A very large dose or amount To prevent excessive intake the Dietary Reference Intakes include a tolerable upper intake level for most vitamins Provitamins Can Be Converted to Vitamins by the Body Provitamins Substances found in foods that can be converted into an active form once they are absorbed Found in foods but are not directly usable by the body must be converted first The best known example is beta caratene which is split into two molecules of vitamin A in the small intestinal cell wall or in the liver cells Preformed Vitamins Substances that are found in active form in foods A family of substances called retinoids that include retinol retinal and retinoic acid These are called preferred vitamin A because they are in a form Vitamin A cid 127 What is vitamin A that the body readily uses Retinol is the most usable and can be converted into retinal or retinoic acid Found only in food from animal sources Added to all processed milk Plant food sources do not contain preformed vitamin A but some do contain provitamin A carotenoids which can be converted to retinol in the body cid 127 More than 600 different carotenoids but only three can be converted to vitamin A beta carotene beta cryptoxanthin and alpha carotene These three provide about 25 to 35 percent of the dietary vitamin A consumed by adults in the United States with the majority of it coming from beta carotene Functions of Vitamin A Rhodopsin Vitamin A is a component of two light sensitive proteins that are essential for vision Bleaching As rhodopsin absorbs incoming light the shape of vitamin A is altered and it detaches from its protein This causes a cascade of events that transmits visual messages