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Kin110_Chapter 7 Vitamins (Water Soluble).docx

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Simon Fraser University
Biomedical Physio & Kines
BPK 110
Gina Whitaker

Kin110 Chapter 7 Vitamins (Water Soluble) Vitamins-organic compounds Fat-soluble & water-soluble Micronutrients found in food -needed only in mg’s or micrograms -amount and type depends on the food source Essential in regulating many body processes Established DRIs help us monitor our vitamin intake Adequate Intake/Recommended Daily Allowances Tolerable upper intake levels (if any) Vitamin Deficiencies can arise from Inadequate intake Increased requirements-metabolic/health state Excessive Loss-excretion of water soluble vitamins Issues from absorption and/or handling of the vitamin within the body (bioavailability) Factors the affect vitamin content of food Amount naturally present + fortification – (processing, preparation & storage factors) Adding Vitamins -government mandated to prevent common deficiencies/promote health -companies trying to increase the marketability of their product Subtracting Vitamins -freshness -light/oxygen exposure -preparation methods -cooking methods Bioavailability-the rate and extent to which a nutrient is absorbed and used by the body Approximately 40-90% of vitamins in food are absorbed Determinants of Vitamin Bioavailability Pre-absorption -efficiency of digestion & transit time through the digestive tract -biological factors influencing absorption -other foods consumed at the same time E.g. Vitamin D will not be absorbed well when taken without food -method of preparation (not same as vitamin content) E.g. steamed vs. raw carrots -sources of the nutrient (food vs. supplements) Other -blood transport systems (fat vs. water soluble vitamins) -fat soluble need to transported by lipids -water soluble may bind to protein carriers in the blood -conversion of pro-vitamins or vitamin precursors into active vitamins in the body Vitamin Absorption In the mouth, chewing breaks food into small particles helping to release vitamins In the stomach, digestion of food releases vitamins. Some niacin is absorbed here The gallbladder releases bile, which emulsifies fat and helps absorb fat-soluble vitamins The pancreas secretes digestive enzymes that aid in the release of vitamins from food In the small intestine, fat soluble vitamins are incorporated into micelles and then absorbed by simple diffusion. Once they are inside the mucosal cells, fat-soluble vitamins are packages into chylomicrons, which enter the lymph before passing into the blood Water-soluble vitamins are absorbed from the small intestine directly into the blood. Many depend on energy-requiring transport systems or must bind to specific molecules in the GI tract to be absorbed. Vitamin B12 is absorbed in the lower portion of the small intestine In the large intestine, bacteria synthesize small amounts of vitamins, some of which are absorbed Water Soluble Fat Soluble Vitamins B Vitamins (choline), Vitamin C A, D, E, & K Absorption Directly into blood With lipid into lymph Transport None required Require protein carriers Storage Free in aqueous compartments In cells associated with fat Excretion Readily via kidneys Not readily Toxicity Only from supplements More likely Requirement Frequently (every 1-3 days) Periodically (weeks to months) Some major functions of vitamins Coenzymes-organic non-protein substances that bind to an enzyme to promote its activity -most B vitamins Antioxidants-substances that decrease the adverse effects of reactive molecules on normal physiological function Free radicals & Antioxidants Reactive oxygen molecules cause oxidative damage by stealing electrons from other compounds, causing changes in their structure and function E.g. Free radicals-one or more unpaired electrons generated by the body or from exposure to the environment Oxidative damage is associated with cancer, diabetes, heart disease, possibly Alzheimer’s and Parkinson’s Antioxidants destroy reactive oxygen molecules E.g. vitamin C, vitamin E, and selenium The water-soluble vitamins B Vitamins, Vitamin C (and Choline?) Not stored–need to be consumed regularly Filtered out of the blood by the kidneys and excreted in the urine More fragile than fat-soluble vitamins (more easily destroyed during processing, etc) The B Vitamins function primarily as coenzymes (not active in their food sources) Bind to enzymes to promote their activity (act as catalysts) -the vitamin combines with a chemical group to form the functional group coenzyme (active vitamin) -the functional coenzyme combines with the incomplete enzyme to from the active enzyme -the active enzyme binds to one or more molecules and accelerates the chemical reaction to form one or more new molecules -the new molecules are released and the enzyme and coenzyme (vitamin) can be reused or separated Important roles in energy metabolism Thiamin (B1) Functions Part of the coenzyme TPP Needed to convert pyruvate to acetyl CoA Needed for the synthesis of the neurotransmitter, acetylcholine Needed for synthesis of the sugars ribose (part of RNA) and deoxyribose (part of DNA) Food Sources Present in small amounts in many foods DRI is easily met with a well-balanced diet Whole & enriched grains (found in the bran layer of the grain) Pork, legumes, nuts, liver, watermelon Easily destroyed by heat Deficiency Primarily affects the nervous system & cardiovascular system Results in Beriberi (“I can’t I can’t”) Symptoms include weakness, fatigue, enlarged heart, cardiac failure, apathy, poor short term memory, confusion, irritability, muscle paralysis Rare in North America, except Wernicke-Korsakoff syndrome (a form of thiamin deficiency associated with alcohol abuse) Symptoms include confusion, psychosis, memory disturbances, coma No known toxicity associated with thiamin Riboflavin (B2) Functions Forms part of the coenzymes FAD & FMN (involved in citric acid cycle, beta-oxidation, respectively) Helps convert other vitamins into their active forms E.g. B2 (with iron & B6) needed for conversion of tryptophan into niacin E.g. B2 need to convert B6 to its coenzyme form Food Sources Small amounts in many foods DRI is easily met with a well-balanced diet Dairy products, red meat, poultry, fish, leafy greens, asparagus, mushrooms, broccoli, whole grains Easily destroyed by UV light Deficiency Usually occurs along with other vitamin deficiencies -similar food sources -riboflavin needed to convert many vitamins to active form Seen in alcoholism Symptoms include inflammation of membranes of the mouth, skin, eyes, and digestive tract, inflamed eyelids, sensitivity to light, sore throat, and cracked lips No known toxicity associated with riboflavin Niacin (B3) Other names include nicotinamide & nicotinic acid Functions Part of the coenzyme NAD which is required for many reactions of energy metabolism Inhibits fat breakdown in adipose tissue -high doses of niacin may lower LDL, raise HDL Food Sources Can be synthesized from the amino acid tryptophan (requires riboflavin, iron and vitamin B6) Diets rich in high quality protein never lack niacin Best sources per kcal -spinach, mushrooms, chicken breast, liver, fish (cod, halibut, tuna) Deficiency Populations at risk -alcoholi
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