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Lecture 7

Lecture 7 - Vitamins.doc

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Department
Health Studies
Course Code
HLTH 230
Professor
Jeffery Lalonde

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Lecture 7 - Vitamins VITAMIN B12 *folate and B12 require each other - symbiotic relationship Roles -involved in synthesis of new cells -helps maintain nerve cells -helps breakdown some fatty acids and a.a. • Vitamin B12 and Folate are closely related (depend on each other for activation) -B12 participates in removal of methyl group for activation of folate coenzyme -B12 coenzyme is activated when folate gives up methyl group to B12 • Digestion 1. Stomach: HCl and pepsin release B12 from proteins it is bound to in food 2. B12 binds with intrinsic factor (secreted in stomach) in the small intestine 3. Intrinsic factor and B12 travel together to the end of the small intestine where the complex is recognized 4. Intrinsic factor is degraded and B12 is absorbed *If B12 is not bound to intrinsic factor, receptors do not recognize B12 for absorption =>need intrinsic factor to absorb B12!!! Recommendations • -only a very small amount required: 2.4 micrograms (very little!!) • Deficiency -generally results from poor absorption, not poor intake -inadequate absorption is likely due to either (secondary deficiency): -lack of HCl acid (B12 not released from dietary proteins) -lack of intrinsic factor (B12 is not recognized for absorption) -deficiency is common in the elderly due to atrophic gastritis -atrophic gastritis (inflammation of stomach): common in older adults -may also occur as a result of iron deficiency or infection with Helicobacter pylori -“without healthy stomach cells, production of HCl and intrinsic factor decreases” Lecture 7 - Vitamins pernicious anemia: blood disorder that reflects a vitamin B12 deficiency caused by a lack of intrinsic factor and characterized by large immature RBC -prolonged inadequate intake from vegan diet may result in a vitamin B12 deficiency -deficiency symptoms take many years to occur -approx. 2000 mcg stored in liver -vitamin B12 is recycled and reabsorbed *linked to stroke -B12 and Folate -*recall: B12 required to convert folate into active form -> large immature RBC will result from B12 deficiency -either folate/B12 will clear up anemia but if folate is given when B12 is needed, result may be devastating neurological symptoms -folate will clear up anemia, however B12 deficiency will again be masked and the nerve sheaths will not be maintained leading to neurological damage -marginal B12 deficiency impairs cognition -advanced neurological symptoms include creeping paralysis -> large RBC are a sign of folate deficiency/Vit. B12 deficiency -if folate is supplemented, will clear up anemia (problem is not fixed! - masks B12 deficiency) -but if it is truly a B12 deficiency, neurological problems still result • no toxic levels found for B12 B12 loss/destruction: • -microwave cooking will help decrease loss of most B vitamins with cooking, not the case for B12 -Microwave heating inactivates B12! (lose B12 by microwaving) • Food sources -almost uniquely found in foods of animal sources -bioavailability greatest in milk and fish -yeast grown on B12 - enriched medium and mixed with medium provides some B12 -B12 found in fermented soy products and sea algae but it is inactive -fortified beverages and fortified foods (ex. soy beverage) - main source for vegans B Vitamins -Thiamin -Riboflavin -Niacin -Biotin -Pantothenic Acid -Vitamin B6 -Folate -Vitamin B12 Lecture 7 - Vitamins B Vitamins Together • have many important roles • often work together -examples: -Folate and B12 -FMN (riboflavin coenzyme) assists the enzyme that converts B6 to PLP -severe riboflavin deficiency can impair B6 activity -both riboflavin and B6 required for conversion of tryptophan to niacin -niacin supply can be diminished bc of inadequate intake of riboflavin/B6 work in pathways all over the body • • B vitamin coenzymes are indispensable to metabolism -do not provide energy! Vitamin-Like Compounds Choline • -essential in diet -can be made from methionine, found as a part of lecithin (synthesis is insufficient) -used by body to make ACh and lecithin -an AI has been established Deficiency • -deficiencies are rare, some is required in diet as production in the body is not adequate -liver damage • Toxicity -low blood pressure, liver damage -body odour, sweating, salivation, reduced growth rate • Food Sources -milk, liver, eggs, peanuts inositol: part of cell membrane structures carnitine: transports long chain fatty acids from cytosol to mitochondria for oxidation inositol and carnitine -can be made by body (not essential nutrients) -not vitamins Lecture 7 - Vitamins VITAMIN C • 250 years ago, crew on ships had 50% chance of living/dying • 2/3 of ship’s crew would die on long trips • only men on short trips were free of scurvy • fruits and vegetables were used up early part of trip • James Lind, British doctor, performed the first nutrition experiment in the mid 1700s to find cure for scurvy Early Experiment • 12 sailors with scurvy were divided into 6 pairs -Cider, Vinegar, Sulfuric Acid, Sea water, Oranges and Lemons, Strong Laxative • Each pair received a supplemental ration • those who received citrus quickly recovered from scurvy • 50 years later, British Navy required lemon/lime juice daily for sailors • Nearly 200 years later...6 carbon compound, ascorbic acid, was in the citrus! -comes from antiscorbutic (VITAMIN C!) Roles 1) Antioxidant a) defends against free radicals -free radical: molecule with one or more unpaired electrons and is therefore unstable and highly reactive -antioxidants donate electrons to the free radicals, makes them more stable -protects other substances from damage b) protects tissues from oxidative stress -oxidative stress: condition where production of oxidants and free radicals exceed body’s ability to handle them and prevent damage -may play an important role in preventing disease 2) As a cofactor in collagen formation -Vitamin C helps to form fibrous structure of collagen -collagen: structural protein from which connective tissues (scars, tendons, ligaments) and foundations of bones and teeth are made -serves as a matrix for bones and teeth formation -cells are held together largely by collagen which is important when the thin capillary walls must expand with each heart beat -helps in scar formation after someone is injured -*recall: proteins are made by stringing together a.a. -for collagen synthesis: -hydroxyproline and hydroxylysine facilitate binding of collagen -> makes collagen fibres strong and rope-like -hydroxylation occurs with help of both vitamin C and iron Lecture 7 - Vitamins 3) A cofactor in other reactions -helps with hydroxylation of carnitine (transports F.A. to mitochondria for oxidation) -participates in conversion of: -tryptophan to serotonin -tyrosine to norepinephrine -assists in making of hormones -ex. vit. C assists in making thyroxine (regulates metabolic rate) 4) In Stress -Vitamin C is increased during stress -adrenal glands (store most vitamin C) release Vitamin C and hormones into blood during stress -stresses include: infections, burns, extreme temp, intakes of toxic metals, smoking, use of aspirin, barbiturates, oral contraceptives -during immune response, a lot of free radicals are produced -free radicals help attack viruses and bacteria with an “oxidative burst” -Vitamin C helps regulate oxidative activity 5) The Common Cold a) some relief of symptoms ← -people have taken Vitamin C for colds for decades ← -mixed studies -> some find no relation, some find fewer colds, shorter symptoms ← -lit. review found those taking at least 200mg Vit C/day had colds 8% shorter in duration b) deactivates histamine -nasal congestion is a result of histamine -like antihistamine, vitamin C deactivates histamine 6) In Disease prevention -possible benefits of Vitamin C -> preventing/treating heart disease, cancer, cataracts -Why is Vitamin C difficult to study? -difficult to study in Canada and U.S. as diet’s typically provide enough for optimal health benefits • Recommendations -10mg daily to prevent overt symptoms of scurvy -at 200mg, absorption reaches a maximum -RDA: women - 75 mg men - 90 mg -smokers requirement increased by 35 mg (bc smoking stresses the body) -higher doses may be recommended by medical professionals for healing -> role of collagen Lecture 7 - Vitamins • Deficiency -scurvy symptoms begin to appear when Vit. C pool falls to about 1/5th of optimal levels -generally after more than 1 month of no Vit C, scurvy begins to appear -scurvy can be easily remedied with intake of Vitamin C -moderate doses around 100 mg can cure scurvy within 5 days -noticeable signs: gums bleed around teeth, blood vessels break under skin -inadequate collagen -> causes further hemorrhaging, muscles degenerate (hrt muscle) *VERY HARD TO BE VITAMIN C DEFICIENT! symptoms: -pinpoint hemorrhages -skin becomes rough, brown, scaly, and dry -wounds fail to heal -teeth become loose -bone rebuilding falters -hysteria and depression may occur -sudden death due to massive internal bleeding • Toxicity -toxicity symptoms are often reported bc people are taking large supplemental doses -symptoms: nausea, abdominal cramps, diarrhea -large amounts: false positives/negatives in urine tests -massive doses: interfere with anti-clotting medicines -may adversely affect people with iron overload -large doses: may make those with kidney disease prone to kidney stones • Destruction -vulnerable to heat and oxygen -juice should be consumed within a week of opening -exposure to air breaks down Vitamin C • Food Sources -citrus fruits, cabbage type vegetables, dark green vegetables (bell peppers, broccoli), strawberries, cantaloupe, lettuce, tomato, potatoes, papaya, mangoes, red bell pepper, kiwi -Vit. C often added to cured meats and lunch meats (not adequate sources) -liver and raw meats -potatoes do not meet daily requirements -scurvy became evident in Ireland during potato famine Not sources of Vitamin C! -milk and milk products -whole grains Lecture 7 - Vitamins The Fat-Soluble Vitamins A, D, E, K (Chapter 12) • require bile for absorption • travel through lymphatic system on absorption before entering blood stream • many require protein carriers for transport in the bloodstream • excesses are stored in liver and adipose tissue • body maintains blood concentration by getting fat soluble vitamins from storage as needed • people can go without needed amount for days, weeks, and years without ill effects as long as average intake meets their needs • toxicity: much more likely bc of their storage and bc they are not readily excreted *we store fat-soluble vitamins and not water-soluble vitamins (absorbed directly into blood) -more likely to cause toxicity because they are stored VITAMIN A & BETA-CAROTENE Vitamin A -first fat-soluble vitamin to be recognized -precursor => beta-carotene -has 3 active forms in the body (collectively known as retinoids) 1) Retinol 2) Retinal 3) Retinoic Acid • foods derived from animals can provide retinyl esters (easily digested and absorbed as retinol in intestine) • cells can convert retinol and retinal to the other active forms of vitamin A as needed conversion of retinol to retinal is reversible, but from retinal to retinoic acid is not • • irreversible change is important bc each active form of vitamin A has a unique function Lecture 7 - Vitamins • foods of plant origin can provide carotenoids • Vitamin A activity -Alpha-carotene -Beta-carotene -Beta-cryptoxanathin • No Vitamin A activity -Lycopene -Lutein -Zeaxanthin Beta Carotene • cleavage of Beta-Carotene in the centre can provide 2 molecules of vitamin A • cleavage may occur at other points yielding only 1 vitamin A molecule • absorption of Beta Carotene is less efficient than Vitamin A • 12 micrograms of Beta Carotene = 1 microgram of Vitamin A • conversion of other carotenoids is less efficient Vitamin A • absorption and transport of Vitamin A in body -absorbed in lymph system -eventually arrives and stored in liver -retinol-binding protein picks up vitamin A in liver, carries it through bloodstream -cells which use vitamin A have special protein receptors for it -need protein to carry it around the body Major Roles: -promoting vision -protein synthesis and cell differentiation -supporting reproduction and growth Vitamin A in Vision helps maintain cornea • • participates in conversion of light energy to nerve impulses at retina -retina contains rhodopsin (opsin and cis-retinal) -cis bind is changed to trans bond when rhodopsin absorbs light -> triggers a nerve impulse of visual information to the brain -light passes through cornea and strikes cells of retina -rhodopsin changes shape -> becomes bleached -with change to trans bond, retinal can no longer stay bonded to opsin -membrane of cell is disturbed, nerve impulse sent to brain -some retinal is then changed back to its active cis form, some may be oxidized to retinoic acid (biological chemical dead end for visual process) -visual activity leads to repeated loss of retinal and requires constant replenishmnt -only 1/1000th of the body’s vitamin A is in retina rhodopsin: pigment molecule composed of opsin (protein) bonded to molecule of retinal Lecture 7 - Vitamins • Vitamin A in protein synthesis and cell differentiation -Cell differentiation: process where cells develop to perform specific functions -Epithelial cells -all body surfaces are covered by epithelial cells -outside -> skin -inside -> mucous membrane -Vitamin A maintains healthy cells in the mucous membrane and promotes the differentiation of epithelial and goblet cells (synthesize and secrete mucous) • Vitamin A in Reproduction and Growth -retinol participates in sperm development -Vit. A supports normal fetal growth and development during pregnancy -Children lacking vit. A fail to grow -if children are supplemented, they gain weight and grow taller -also participates in bone remodeling for growth -Vit. A assists enzymes in breaking down parts of bone to allow growth -bone remodeling: dismantling and refo
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