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Vitamins: Essential Dietary Components
• Essential organic substances– Water-soluble: Vitamin B complex and C– Fat-soluble: Vitamins A, D, E and K
• Absorption of vitamins• Malabsorption of vitamins• Transport of vitamins• Storage of vitamins in the body• Vitamin Toxicity
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Vitamin A Needs
• RDA– Men
• 900 micrograms– Women
• 700 micrograms
• Daily Value– Approximately 1,000 micrograms
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Functions of Vitamin A (Retinoids)
• Growth and Development• Cell Differentiation• Vision
– rhodopsin
• Immune Function– Maintenance of the epithelium
• Use of vitamin A analogs in Dermatology
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Vitamin A Diseases
• Rare in North America, but major problem in developing countries
• Deficiencies– Night blindness– Xerophthalmia (irreversible blindness)– Follicular hyperkeratosis
• Toxicities– Hypervitaminosis A– Upper Limit: 3000 micrograms/d– Acute and chronic toxicity
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Vitamin D
• “Conditional” vitamin or a prohormone• Vitamin D2 in Foods:
– Fatty fish, cod liver oil, fortified dairy products and some fortified breakfast cereals
• Vitamin D3 is formed in skin from cholesterol:– Sunlight changes 7-dehydrocholesterol to cholecalciferol– Travels to liver and then kidneys, where converted to
bioactive form (calcitriol)• Requirement: sunlight 2-3 times/week for 10-15min
– Several factors influence this
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Vitamin D Needs
• RDA– Under age 70: 15 µg – Over 70: 20 µg
• Breastfed infants: 10 µg • Daily Value: 10 µg
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Functions of Vitamin D
• Calcitriol is the active form• Calcium and Phosphorus Homeostasis
– Aids in increasing absorption of Ca & P– Aids in releasing Ca & P from bone, if blood
levels are low
• Bone Health• Immune Function• Chronic diseases (see Perspective from the Field)
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Vitamin D Diseases
• Deficiencies– Children: rickets– Adults: osteomalacia
• Toxicities– Does not occur from sunlight or dietary sources– Can occur with supplementation– Upper Limit: 100 µg – Calcium deposits in soft tissues
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Vitamin E
• 8 compounds– 4 tocopherols– 4 tocotrienols
• Dietary sources:– Plant oils (e.g., canola), wheat germ, avocado,
almonds, peanuts and sunflower seeds
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Vitamin E Needs
• RDA– 15 mg of alpha-tocopherol– Based on hemolysis prevention– Adults consume approximately 2/3 the RDA
• Daily Value– 30 IU (approximately 20 mg)
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Vitamin E Functions
• Antioxidant– Stops lipid
peroxidation (chain reactions) caused by free radicals
– Works with vitamin C
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Vitamin E Diseases• Deficiency
– Hemolytic anemia -- rare in healthy people– Pre-term infants and smokers are most susceptible– Immune function impairment and neurological
changes
• Toxicity– Can interfere with Vitamin K and cause
hemorrhaging– Upper Limit:
• 1000mg natural sources (1100 IU from synthetic sources)
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Vitamin K
• Menaquinones– Synthesized by bacteria in colon (10%)– From fish oils and meats
• Phylloquinones– From plants: green leafy vegetables, broccoli,
peas, and green beans– Most biologically active
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Vitamin K Needs
• AI– Women
• 90 micrograms daily
– Men• 120 micrograms daily
• Daily Value– 80 micrograms
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Vitamin K Functions & Diseases
• Functions– Synthesis of blood clotting factors– Bone metabolism
• Deficiency is rare– Newborns; long-term antibiotic use; fat malabsorption
• Toxicity– No UL
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Dietary Supplements: Healthful or Harmful?
• Dietary Supplement Health and Education Act of 1994 (DSHEA)
• Definition:– A vitamin, a mineral, an amino acid, an herb, a
botanical, a plant extract, or a combination of any of the above
• Quality, purity, and consistency are not closely monitored by FDA