Fat-Soluble Vitamins

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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 in Foods

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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

Vitamin E in Foods

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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

Vitamin K in Foods

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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

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Supplementation Is Not a Substitute for a Poor Diet

• Some individuals may benefit

• Things to look for:– No more than 100% Daily Value– USP certification– Diet and supplement shouldn’t exceed ULs– Check for superfluous ingredients