Lecture 9- Vitamins Flashcards
What is the history of vitamins?
- Purified diets of carbohydrate, protein, fat, minerals and water were not capable of normal growth
- “Accessorygrowthfactors”
- Funk, a Polish biochemist, isolated an anti-berberi substance from rice polishings
- Nameditvitamine
- An amine
- Vital for life
What are vitamins?
- Essential organic compounds required in very small amounts (micronutrients) involved in fundamental functions of the body
- Unrelated chemically
- Not only amines so “e” was dropped
- Not metabolic fuels (like glucose or fatty acids) or structural nutrients (like amino acids)
- Regulators (catalysts) of reactions, some of which are involved in energy metabolism
Are all vitamins metabolically essential?
• All vitamins are metabolically essential but not all required in the diet • Most mammals can synthesise vitamin C; not humans, primates or red wing
bulbuls
• No mammal can synthesize B vitamins but rumen bacteria do
• Some function as vitamins after undergoing a chemical change • Provitamins (e.g., β-carotene to vitamin A)
What is the classification of vitamins?
- Based on solubility in the laboratory, but solubility greatly influences how the body absorbs, transports and stores vitamins
- Fat-soluble
- Vitamins A, D, E and K
- Water-soluble
- B vitamins and vitamin C
What are the fat-soluble vitamins?
- A Retinol
- D2 Ergocalciferol
- D3 Cholecalciferol
- E Tocopherol
- K Phylloquinone
What are the characteristics of fat-soluble vitamins?
- Absorbed with dietary fat in small intestine
- 40-90% absorption efficiency
- Absorption typically regulated by need • needabsorption
- Transported away from small intestine in chylomicrons via blood and lymph (depending on size)
- Liver either stores the vitamin or repackages it for delivery to other cells
- Excess vitamin accumulates in liver and adipose
- Toxicities can occur; almost always associated with supplement use (not foods)
What are the characteristics of water-soluble vitamins?
• Absorbed at the small intestine
• Absorption often highly regulated by either other vitamins or binding proteins in
the small intestine
• Transported away from small intestine in blood
• Typically not stored; instead, kidney filters excess into urine • Thus, more important to get these vitamins daily.
• Toxicities almost unheard of
What happens with fat-soluble vitamins?
- Stored in fatty tissue
- Destroyed by heat
- Destroyed by light (photolysis)
- Unstable in chemicals
- Available in various forms
What are the 3 forms of vitamin A?
- Retinal
- Retinoic acid
- Retinol (key player; can be converted to other forms)
What is vitamin A synthesis and storage like?
- β-carotene (a carotenoid or pigment) in yellow/orange foods is a potent provitamin A
- β-carotene is converted to vitamin A in the intestinal mucosa • >80 provitamins (not all → vit A)
- 90% is stored in liver, mainly as the ester, retinyl palmitate • Carotenoids can be stored in adipose tissue
What are the sources of vitamin A and its precursors?
• Animal sources • Liver • Milk • Plant sources • Alfalfa • Green leafy vegetables • Red veggies (carrots, tomatoes etc) -Generally green = good source of β-Carotene
What are the functions of vitamin A?
- Vision, especially night vision • Cell growth (retinoic acid)
- Immunity
- Reproduction
- Functions of vitamin A
- Component of visual pigments in the retina
- Growth => cell proliferation and differentiation
- Formation & protection of epithelial tissues and mucous membranes • Antioxidant functions
- Immune function
What are some characteristics of carotenoids?
- Additional physiologic effects
- Serving as an “antioxidant”
- Remove excess “electrons” from cell system
- Electrons (free radicals) damage cells and DNA
- Can cause mutations
- Protecting from cancer (related to antioxidant function?)
- Protecting from heart disease?
- Readily destroyed by oxidation
What happens in vitamin A deficiency?
- Main symptoms • Nightblindness
- Dryskin
- Immunedysfunction
- Rare in industrialized world
- Leading cause of blindness in areas of poverty
- Deficiency symptoms • Night blindness
- Degeneration of mucous membranes in the eye, mouth, digestive tract, and reproductive tract
- ability to synthesise mucous increased infection • Impaired spermatogenesis
- Foetal growth failure abortion & foetal resorption
- Disorganised bone growth
- Defective immune system activity
What is the toxicity of vitamin A?
- Skeletal malformations, spontaneous fractures, internal hemorrhages
- Upper safe levels are 4-10x requirements in nonruminants and 30x in ruminants
- Topical (cosmetic) retinoids can be dangerous • 12 months retention time in body tissues
- Can cause birth defects
- Hypervitaminosis A in humans
- Polar explorers eating polar bear or seal liver • Self-medication and over prescription
What is vitamin D?
- Not always essential
- Body can make it if exposed to enough sunlight
- Not really a vitamin?
- Made from cholesterol in the skin
- Functions
- Regulates calcium absorptionbone health • Cell growth
What are sources of vitamin D?
- Not found naturally in many foods
- Fluid milk products are fortified with vitamins A and D • Oily fish
- Egg yolk
- Butter
- Liver
- Difficult for vegetarians
What are the symptoms of vitamin D deficiency?
- Children
- Rickets
- Failure of bones to grow properly.
- Results in “bowed” legs.
- Adults
- Osteoporosis (porous bones)
- Associated with fracturesvery serious for the elderly
- Deficiency symptoms
- Mainly bone disorders
- Rickets incomplete calcification of bones
- Osteomalacia reabsorption of bone (older animals)
- Cattle Swollen hocks and knees
- Pigs Enlarged joints, broken bones, joint stiffness, paralysis
- Poultry Soft and rubbery bones and beaks
- retarded growth
- egg production, poor egg-shell quality
Who is vulnerable with vitamin D deficiency?
- Who is vulnerable?
- Thought that >50% of US and 35% of Australians are somewhat deficient. • What about sunscreen?
- Deficiencies more common in very North and South ( sun exposure)
- People who have trouble absorbing fats (e.g., cystic fibrosis)
- Extremely low fat diets
What are the functions of vitamin E?
- Functions
- Antioxidant
- Protects cell membranes from free radicals
- Protects lungs from pollutants
- Protects DNA
- Protects heart
- Others?
- Functions of vitamin E
- Antioxidant, (also works with selenium)
- Scavenges oxygen and free radicals
- Prevents damage to fatty acids in cell membranes • Nucleic acid and protein metabolism
- Mitochondrial electron transport
What are plant sources of vitamin E?
- Plant sources • Wheatgerm
- Vegetable and seed oils • Little in animal sources
- Beef fed high levels of vitamin E right before slaughter so now a source • Improves shelf life
What is vitamin E deficiency like?
- Very rare, except in people who have difficulty absorbing fat
- Symptoms
- Breakdown of red blood cellsanaemia
- Deficiency symptoms
- muscle degeneration (myopathy)
- “White muscle disease” in skeletal muscle • degeneration of testicles
- Chicks muscular dystrophy
- Encephalomalacia (necrosis of the brain)s
- Exudative diathesis (oedema caused abnormal permeability of capillaries)
What are the vitamin K functions?
- Functions
- Blood clotting Bone formation
- Vitamin K does not cross the placenta • Gut produces little in infants
- Low levels in breast milk
- Australian babies are injected with vitamin K at birth
What are some characteristics of vitamin K?
- Chemical nature
- Exists in three forms
- All forms converted to menaquinone in the liver
- Vitamin K is table at room temp, but is photolabile
- Functions
- Bloodclotting
- Involved in synthesis of prothrombin
- Thrombin converts fibrinogen into fibrin
- Deficiency symptoms
- BirdsHaemorrghages
- Birds Anaemia in chicks + delayed clotting time
What are the sources of vitamin K?
- Bacteria in the large intestine (10-15%) or rumen
- Plant sources
- Green leafy vegetables
- Some oils • Broccoli
- Animal sources • Liver
- Milk
What are vitamin K deficiency symptoms?
- Very rare, except in people who have difficulty absorbing fat (e.g., cystic fibrosis, Crohn’s disease) or using lots of antibiotics (they kill the bacteria in large intestine)
- Symptom: bleeding
What are some interactions of vitamin K and other chemicals?
- Dicoumarol and warfarin (rat poison) are antagonists of vitamin K
- Dicoumarol found in mouldy clover hay • Sweet clover disease
What are water-soluble vitamins?
-B vitamins and vitamin C
What was the case with vitamins B?
• Originally thought to be one vitamin
• 8 of them
• Act primarily as coenzymes in metabolic pathways • Important for ATP production!!!
-• Dietary requirement is linked closely to metabolic rate (i.e., production)
• Ruminant requirements for B vitamins is usually met by rumen bacterial synthesis
• Hindgut bacterial synthesis and absorption is insufficient to meet full requirements for a horse
What are the sources of vitamins B?
- VARIETYof foods!
- Plant sources
- Found in fibrous portion of plants
- Most cereals and grain products are enriched
- Animal sources
- Liver
- Milk
- Egg
- Beef, pork and chicken
