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
