Fat-soluble Vitamins

Overview of Vitamins

• Overview
  • Are essential organic substances needed in small amounts in the diet for normal function, growth, and maintenance of body tissues
  • Vitamins A, D, E, and K dissolve in organic solvents whereas the B vitamins and vitamin C dissolve in water
  • Usually cant be synthesized in sufficient quantities or synthesized at all
  • Used in correcting deficiency diseases and some used to treat non-deficiency diseases
  • Found in plant and animal sources supply vitamins in the diet
  • Little difference between “natural” vitamins isolated from foods versus “synthesized”
• Historical
  • "Vita" or essence of life and when deficiency occurs may cause disease
  • Vitamin C deficiency - Scurvy, first record in 1500 B.C. but sailors carried lime juice to prevent illness
  • Thiman deficiency - Beri beri, late 1800s, Dr. Eijkman, essence in outer coating of rice prevents illness
    
  • Correlation between chemicals factors and cures for deficiencies
  • Many discovered during the late 19th, early 20th century
  • As they were discovered were labeled using letters (A, B, C, D, E) until structural diferences discovered changed the nomenclature of vitamins
    
  • Compounds continually identified as being essential and in the future may be classified as vitamins (e.g. choline, carnitine, inositol, taurine and lipoic acid)
    
• Storage
  • Fat-soluble vitamins are not readily excreted and stored in fat cells
  • Water-soluble vitamins are readily excreted from the body
• Vitamin Toxicity
  • Fat-soluble vitamins are not excreted readily and because they are stored in body cells, accumulation may cause toxicity
  • Vitamin A and D toxicities are observed more often then others
• Absorption varies depending on the food source
  
• Preservation of vitamins in food
  • Vitamins can be lost as a result of: improper storage and excessive cooking

Vitamin A

• Vitamin A is a generic term for a class of compounds called retinoids
• Types of retinoids: retinol, retinal, and retinoic acid
• Carotenoids: pigment in fruits and vegetables used in forming vitamin A
• Alpha & Beta-carotene are examples of provitamins converted into vitamin A (retinol)
• The release of vitamin A from food requires bile, digestive enzymes (lipase) from the pancreas and intestinal tract, and integration into micelles
• 90% of vitamin A absorbed in small intestine
• Retinoids stored in liver and carotenoids stored in liver and adipose
• Cellular Retinoid-Binding Proteins (CRBP or RBP) - needed for the transport of retinoids into cell
• Functions:
  • Visual
    • Retinal in retina of the eye turns visual light into nerve signals to the brain
    • Retinoic acid maintains normal differentiation of the cells that make up the various structural components of the eye
  • Cell differentiation – nuclear retinoid (RAR and RXR) receptors bind to DNA and cause gene expression
    • Used in growth and differentiation of epithelial, nervous, bone tissues
  • Immunity – increases cell differentiation – produce cells involved in specific (e.g., lymphocytes) and nonspecific immunologic defenses (e.g., mucosal surfaces)
    
• Deficiency
  • Hypovitaminosis A
    
  • Xerophthalmia
  • Bitot’s spots (keratin deposited in conjunctiva; associated with night blindness)
  • Follicular hyperkeratosis (protein keratin deposited around hair follicle)
  • Xerosis
  • Immune suppression
  • Anemia
  • Impaired tissue growth
• Dietary Sources
  • Liver, sweet potato, carrots, spinach, mango, acorn, squash, kale, broccoli, margarine, peaches, apricots, cantaloupes, papaya
• RDA
  • RAE’s (retinol activity equivalents) versus IU’s
  • Men 900 ug RAE/day, women 700 ug RAE/day
  • Men 3000 IU/day, women 2330 IU/day
• Toxicity
  • Hypervitaminosis A
  • Caused by excess dosages (100 times RDA)
  • Can be fatal (13,000 times RDA)
  • Chronic: liver damage, hair loss, bone/muscle pain, loss of appetite, dry skin and mucous membranes, hemorrhages, coma
  • Acute: gastrointestinal upsets/nausea, headaches, dizziness, muscle contraction

Vitamin D

• Two nutritionally important forms: vitamin D₂ (ergocalciferol) which is found in plants and vitamin D₃ (cholecalciferol) which is synthesized in the body from cholesterol
• Conversion in skin: provitamin D (a form of cholesterol) is converted to previtamin D₃ is converted to vitamin D₃
• D₃ must be metabolized in the liver before becoming the active form of vitamin D
• 80% of vitamin D is absorbed in small intestine
• Carried by proteins in blood stream
• Formation of hormone form (Calcidiol and Calitriol) of vitamin D occurs in the liver and kidneys
• Functions of vitamin D:
  • Maintains serum calcium and phosphorus concentrations within the range that supports neuromuscular function and bone calcification
  • Calcitriol causes calcium to be absorbed by kidneys and intestines and also causes calcium to be released from bone
• Deficiency
  • Rickets (children) and Osteomalacia (adults)
    
  • Decreased calcium and phosphorus levels and thus soften/weakens bone tissue
    
• Dietary sources
  • Fortified milk, margarine, butter, cereals, egg yolks, liver, fatty fish
• AI (adequate intake)
  • 5 ug/day (19-50yrs)
  • 10 ug/day (51-70yrs)
  • 15 ug/day (>70yrs)
• Toxicity
  • Hypervitaminosis D
  • 5 times the AI is dangerous for infants, 10 times the AI for adults
  • Calcification of soft tissue, growth retardation, excess calcium excretion via the kidneys (kidney stones), headaches, muscle weakness, fatigue, excessive thirst

Vitamin E

• Family of eight antioxidants, four tocopherols, alpha-, beta-, gamma- and delta-, and four tocotrienols (also alpha-, beta-, gamma- and delta-)
• Alpha-tocopherol is most active form
• The release of vitamin E from food requires bile, digestive enzymes from the pancreas and intestinal tract, and integration into micelles
• Vitamin E is stored in liver and adipose tissue
• Functions:
  • Antioxidant
  • Prevents propagation of free radicals
  • Protects other substances from oxidation by being oxidized itself
  • Also protects polyunsaturated fatty acids and vitamin A
• Dietary sources
  • Polyunsaturated plant oils (margarine, salad dressings, shortenings), leafy green vegetables, wheat germ, whole-grains, liver, egg yolks, nuts (esp. almonds), seeds (esp. sunflower)
• Deficiencies
  • Hemolysis of red blood cells, anemia, degeneration of sensory neurons
• RDA
  • 15mg/day
• Toxicity
  • Few symptoms (nausea, fatigue, blurred vision, augmentation of anti-clotting medications)

Vitamin K

• Two forms: Vitamin K₁ Phyllaquinones (plant source) and vitamin K₂ menaquinone (fish oils and meats)
• 80% of dietary vitamin K is absorbed
• The release of vitamin K from food requires bile, digestive enzymes from the pancreas and intestinal tract, and integration into micelles
• Functions:
  • Contributes to the synthesis of seven blood clotting factors
  • Cofactor for enzymes
• Dietary sources
  • Liver, green and leafy vegetables, broccoli, peas, and green beans, milk
• Deficiencies
  • May occur as a result of inadequate fat absorption and/or antibiotic consumption
  • Excessive bleeding may occur
• RDA
  • Men 120 ug/day
  • Women 90 ug/day
• Toxicity
  • May interfere with anti-clotting medication