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What Are Vitamins?• Vitamins: Essential nutrients that your body needs in small amounts to grow, reproduce, and maintain good health.• 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.• 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.• Stored in body until needed.• Can be toxic in high doses.• Needed in small amounts.• Water Soluble: Vitamins B and C• Absorbed with water and enter bloodstream directly.• Most are absorbed in the upper portion of the small intestine, although vitamin B12 is absorbed in the lower part of the small intestine.• Not stored in body. Excess amounts are excreted.• Needed in small amounts.• Not toxic, but excess can be harmful.• Some Vitamins Function as Antioxidants:• Antioxidants: Substances that neutralize free radicals. Vitamins A, C, and E and beta-carotene are antioxidants.• 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 chronicdiseases.• 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 ultravioletrays on unprotected skin.• 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, andbeta-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.• 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 theformation of a micelle to be absorbed.• Vitamins in plant foods are typically less bioavailable than those in animal foods because plant fiber can trap vitamins.• 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.• 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.• Reduce Cooking Time.• 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 vitaminC after cooking than if they were boiled.• Keep Your Food Cool.• Cooler temperatures help preserve vitamins.• 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.• The excess vitamins can damage cells, sometimes permanently.• 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.Vitamin A• What is vitamin A?• A family of substances called retinoids that include retinol, retinal, and retinoic acid. These are called preferred vitamin A because they are in a formthat 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.• 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 frombeta-carotene.• Functions of Vitamin A:• Vitamin A is a component of two light-sensitive proteins that are essential for vision.• Rhodopsin• Bleaching: As rhodopsin absorbs incoming light, the shape of vitamin A is altered, and it detaches from its protein. This causes a cascade of eventsthat transmits visual messages through the optic nerve to the brain.• More sensitive to light than iodopsin and is


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UMaine FSN 101 - Lecture notes

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