Post on 05-Apr-2018
Vitamins• Essential organic substances• Produce deficiency symptoms when
missing from diet • Yield no energy (kcals)• Basic functions
– Facilitate energy-yielding chemical reactions– Function as co-enzymes
Vitamins
• 13 known specific nutrients• Involved in almost every metabolic
process• Minute amounts needed (micronutrients)• Body cannot make (indispensible)• Fat soluble• Water soluble
Vitamins
• Named in order of discovery• Megadose (>10x needs) to correct
deficiency– Vitamin C – scurvy– Vitamin D – psoriasis
• Synthetic vs food sources– Vitamin E – natural form– Folic acid – synthetic form
• All vitamins thought to be discovered
Preservation of Vitamins
• Decreased vitamin content– Improper storage– Excessive cooking– Exposure to light, heat, air, water, and alkalinity
• Eat foods soon after harvest• Freeze foods not consumed within a few
days• Blanching destroys enzymes
– Slows down vitamin degradation
Fat-Soluble Vitamins Overview
• Dissolve in organic solvents• Not readily excreted; toxicity• Absorbed with fat
– Problem if fat malabsorption present• Transported like fat in chylomicrons
– (40-90% absorbed)
Vitamin A
• First vitamin discovered• Reported as essential in 1913• Egyptians and Greeks understood curative
value of liver-rich source of Vitamin A
Vitamin A
• Retinoids –– Preformed vitamin A– Fish and organ meats
• Carotenoids– Provitamin A
• Beta-carotene – Precursors to Vitamin A
Vitamin A
• Liver– Clears Vitamin A from chylomicrons– Main storage place– Targets – most cells of body– Retinoid form greatest concentration
Vitamin A
• Deficiency - most common cause of nonaccidental blindness
• Required in eye for:– Transforming light into neural signals needed
for vision– Maintain cellular differentiation for
• Conjunctival membranes• Cornea• Ocular structures
Vitamin A
• Deficiencies– Night blindness
• Inability to adjust to dim light– Xeropthalmia
• Decreased mucus production - dry eyes – Epithelial cells
• Barriers against infections– Growth, development, reproduction
• Prevents fetal malformations• Failure of embryo to develop
Vitamin A
• Cardiovascular disease– Maybe through antioxidant properties
• Carotenoids
• Cancers– Animal studies primarily– Skin, breast, liver, colon, prostate, lung – Prevent or delay
Vitamin A
• Toxicity– Retinoids may expand and destabilize
membranes• Joint and bone pain
– Teratogenic effects• Spontaneous abortions• Birth defects (1st trimester)
Vitamin A
• Sources– Dark green and yellow-orange vegetables
• Spinach, broccoli, carrots, sweet potatoes
Recommended Amounts for Vitamin A
• 900 ug RAE (retinol activity equivalents) for men
• 700 ug RAE for women• Daily Value is 1000 ug (RAE)• Upper Level is 3000 ug or 10,000 IU
(RAE of preformed)• Much stored in the liver• No separate RDA for carotenoids
Vitamin D
• Prohormone• Cholesterol-like substance converted to
prohormone D• Enzymes in liver and kidneys convert to
active hormone form• Synthesized from sun exposure (90%)
– Sunscreen SPF >8 decreases synthesis 95%– Expose hands, face, arms 2-3 x/week for 5-10
minutes each time (more for darker skin)
Vitamin D
• Insufficient sun exposure makes this a vitamin
• Use stored Vitamin D in winter, need dietary source
• 80% of dietary Vitamin D absorbed
Functions of Vitamin D
• Regulates blood calcium– Along with the parathyroid hormone– Regulates calcium + phosphorus absorption
• From intestine– Reduces kidney excretion of calcium– Regulates calcium deposition in bones
• Influences normal cell development– Linked to reduction of breast, colon, and
prostate cancer
Role in Bone Formation• Vitamin D hormone
– Causes calcium + phosphorus to deposit in the bones– Strengthens bones
• Rickets is the result of low vitamin D – Breastfed infants with little sun exposure– 1650 recognition of disease– 1822, 1889 observations regarding urban vs rural– Cod liver oil – remedy (18th, 19th centuries)– 1930’s addition of provitamin D to milk
• Osteomalacia (soft bones) – Rickets-like disease in adults– Bones lose minerals and become porous
Food Sources of Vitamin D
• Sources– Fatty fish (salmon, herring)– Fortified milk, yogurt– Some fortified cereal
• Food not a significant source of Vitamin D• Casual sun exposure usually sufficient
Adequate Intake (AI) for Vitamin D
• 5 ug/d (200 IU/day) for adults under age 51
• 10-15 ug/day (400 - 600 IU/day) for older adults– May need combination of fortified foods
and supplements
Toxicity Warning
• Vitamin D can be very toxic, especially in infancy and childhood
• Upper Level is 50 ug/day• Results in
– Over-absorption of calcium (hypercalcemia), – Calcium deposits in organs and blood
vessels– Growth retardation– Cell death
• Tanning does not result in toxic levels
Vitamin E
• Vitamin looking for a disease• Role in some metabolic function? • Vitamin E activity depends on “antioxidant
network”– Antioxidants and antioxidant enzymes
maintain E in unoxidized state– E ready to intercept and scavenge radicals
• Prevents spread of free radical damage in cell membranes, DNA, cell components
Vitamin E
• Benefits– May help prevent cardiovascular disease– Cancer – Improves vitamin A absorption– Helps metabolize iron in cells– Maintains nervous system, immune function
Vitamin E
• Upper Level is 1,000 mg/day (supplementary alpha-tocopherol)– Most active form
• Upper Level is 1500 IU (natural sources) or 1100 IU (synthetic forms)– Research ongoing regarding excess intake
Vitamin E
• Toxic effects– Inhibit vitamin K metabolism and
anticoagulants • Reduced clotting
– Possible hemorrhage– Muscle weakness, headaches, nausea
Vitamin K (“Koagulation”)
• Synthesized by bacteria in the colon and absorbed– 10% of that needed– Balance comes from diet
• Role in coagulation process– Activates blood-clotting factors
• Role in calcium-binding potential– Activates proteins that help Ca binding in
bone, muscle, kidneys
Food Sources of Vitamin K
• Liver• Green leafy vegetables• Broccoli• Peas• Green beans• Resistant to cooking losses• Limited vitamin K stored in the body
Adequate Intake for Vitamin K
• 90 ug/day for women• 120 ug/day for men• Excess vitamins A and E
– Interferes with vitamin K– May cause hemorrhage and fractures
• Newborns – Routinely injected with vitamin K– Breast milk is a poor source
• Toxicity unlikely; readily excreted