Lecture 35 Flashcards
Vitamins
1
Q
vitamin
A
essential for normal growth and nutrition and are required in small quanities in the diet because they cannot be synthesized by the body
pg 877
2
Q
minimizing vitamin losses
A
- prevent enzymatic destruction: refrigerate most fruits, vegetables, and juices to slow breakdown of vitamins
- protect from light and air: store milk and enriched grain products in opaque containers to limit riboflavin losses, store cut fruits and vegetables in the refrigerator in airtight wrappers, reseal juice containers before refrigerating
- prevent heat destruction or losses in water: wash intact fruits and veggies before cutting or peeling to prevent vitamin losses during washing; cook fruits and veggies in a microwave oven, or quickly stir-fry, or steam them over a small amount of water to prevent vitamin loss in cooking water; recapture dissolved vitamins by using cooking water for soups, stews, or gravies; avoid high temperatures and long cooking times
pg 877
3
Q
fat soluble vitamins
A
- A, D, E, K
- toxicity possible because stored in fat and liver
- malabsorption with steatorrhea (cystic fibrosis)
- reduced fat intake may cause deficiency -> need to consume with fat, drugs that block fat absorption
pg 879
4
Q
vitamin A -> retinoids
A
retinol:
- preformed vitamin A, storage form
- retinol released from liver transported through blood to extrahepatic tissue by retinol-binding protein (RBP) complexed with transthyretin (TTR)
retinal:
- derived from oxidation of retinol
- readily inconvertible (retinol to retinal)
retinoic acid:
- oxidized from retinal (cannot be reduced back)
- excreted form
β-carotene:
- provitamin - oxidatively cleaved in intestine to release two molecules of retinal - inefficient
- genetic variations in β-carotene 15,15’-oxygenase
vitamin A is a potent mutagen in gene expression
pg 881
5
Q
retinoic acid
A
growth and differentiation
- retinoic acid binds to retinoic acid receptor (RAR) in nucleus of target tissues (epithelial tissue)
- binds to response element -> recruits activators or repressors and regulates expression of retinoic-dependent protein (e.g. keratin) -> epithelial tissue integrity by regulating differentiation and mucus secretion
- normal growth in children
- bone remodeling
pg 882
6
Q
retinol and retinal
A
reproduction (normal levels)
- supports spermatogenesis
- normal fetal development (prevents fetal resorption)
pg 882
7
Q
sources of vitamin A
A
- milk, cheese, cream, butter, fortified margarine, eggs, liver
- β-carotene: spinach, other dark green leafy veggies, apricots, cantaloupe, squash, carrots, sweet potatoes, pumpkin
8
Q
retinal: visual cycle
A
- 11-cis retinal bound to protein opsin in rhodopsin (a visual protein, a G-protein coupled receptor)
- exposure to light -> rhodopsin bleaching -> photochemical isomerization -> decreased cGMP -> activates G protein transducin -> trigger nerve impulse -> transmitted to optic nerve
- regeneration of all trans retinal
- cell membrane rich in n-3 PUFA can increase the efficiency of rhodopsin
vitamin A in the eye maintains a healthy cornea
pg 883
9
Q
hypovitaminosis A
A
- takes a year or more to develop a deficiency
- impaired immunity correlates with vitamin A deficiency in children -> the goals of WHO include vitamin A supplementation, vitamin A declines during infection
- changes in epithelial cells results in keratinization -> rough, dry, and scaly skin
Eyes
- night blindness (nyctalopia): first detectable sign
- can be a loss of visual cells
- blindness (severe deficiency)
- xerophthalmia
- xerosis is the first stage where the conjunctiva and cornea become dry and hard -> coneal ulcers -> opaque scare tissue -> blindness
pg 884-885
10
Q
pharmaceutical forms of vitamin A
A
skin conditions:
- retinoic acid derivative -> tretinoin used for treating mild acne and skin aging -> topical use (e.g. retin-A)
- isotretinoin is teratogenic -> contraindicated in women with childbearing potential (e.g. absorica) -> lethal for fetuses (iPLEDGE program required)
pg 886
11
Q
hypervitaminosis A
A
- can occur with concentrated amounts of the preformed vitamin A from animal foods, fortified foods, or supplements
- consuming extremely excessive amounts of β-carotene from supplements can be harmful
- acute toxicity symptoms include blurred vision, nausea, vomiting, vertigo, headaches, and pressure in the skull
- chronic toxicity -> liver damage -> bone defects (increased osteoclast activity)
pg 887
12
Q
vitamin D -> calcitriol
A
- cholecalciferol transported to liver bound to vitamin D-binding protein
- plant version is vitamin D2 or ergocalciferol
- 25-hydroxycholecalciferol -> predominant form of vitamin D in serum
- formation of active form of vitamin D -> 1,25 dihydroxycholecalciferol (calcitriol) is strictly regulated by serum phosphate (PO43-) and calcium (Ca2+) ion concentrations
- calcitriol and PTH work together to regulate serum levels of calcium and phosphorus
- nutrient of public health concern
pg 889
13
Q
serum 25-hydroxyvitamin D concentrations and health
A
> 20 ng/mL typically considered adequate for bone and overall health in healthy individuals
pg 890
14
Q
sources of vitamin D
A
exposure to sunlight necessary to maintain adequate vitamin D
- sufficient synthesis with five to ten minutes of sun exposure few times a week
- higher melanin needs more time
- sunscreens with SPF > 8 inhibit vitamin D synthesis
- low levels of vitamin D common at end of winter months and in northern latitudes (above 40th parallel)
food sources
- few animal foods provide significant source: eggs, liver, butter, some fatty fish, maybe mushrooms
- fortified foods: milk, margarine, cereals, infant formulas
pg 891
15
Q
clinical indications - vitamin D
A
Nutritional Rickets
- bone demineralization (loss of calcium) -> rickets in children and osteomalacia in adults
- rickets: continued formation of collage matrix in bone with incomplete mineralization -> soft bones
- osteomalacia: demineralization of pre-existing bones -> increased susceptibility to fracture
Hypoparathyroidism
- lack of PTH -> hyperphosphatemia and hypocalcemia
Toxicity
- enhanced calcium absorption -> hypercalcemia -> deposition of calcium salts in soft tissues
- kidney stones
- vascular calcification
pg 892
16
Q
vitamin E -> tocopherol
A
- α-tocopherol is most biologically relevant
- works as an antioxidant (prevent non-enzymatic oxidation) -> prevents peroxidation of PUFA, LDL oxidation, cell membrane
- vitamin requirement increases with increase intake of PUFA
- breast milk provides vitamin E to newborn
- in adults, deficiency because of defective lipid absorption or transport
- found in lipid bilayers
- sources: leafy green veggies, plant oils, whole grains, liver, egg yolks, nuts and seeds
pg 894
17
Q
vitamin E deficiency
A
- primary deficiency due to inadequate intake is rare
Symptoms:
- loss of muscle coordination and reflexes
- impaired vision and speech
- nerve damage
- erythrocyte hemolysis: premature infants, hemolytic anemia can be treated with vitamin E
pg 895
18
Q
vitamin K -> k for koagulation
A
- several active forms: phylloquinone in plants (K1), menanquinone in intestinal bacteria (K2), menadiaone (synthetic vitamin K -> K2)
- hepatic synthesis of functional blood clotting proteins -> vitamin K-dependent carboxylation of several γ-glutamic acid residues to γ-carboxyglutamate (Gla) by the enzyme g-glutamyl carboxylase
- warfarin (rat poison -> anti-coagulant in low doses) inhibits regeneration of hydroquinone form of vitamin K from epoxide form by the enzyme vitamin K epoxide reductase (VKOR)
- bacterial synthesis in the digestive tract, liver, leafy green veggies (K1), milk, fermented foods (K2)
pg 897
19
Q
carboxyglutamate (Gla) importance
A
- prothombin interaction with membrane
- Gla is a strong chelator of positively charged Ca2+
- prothombin-calcium complex binds to negatively charged membrane phospholipids on the surface of the damaged endothelium and platelets -> increases the rate of proteolytic conversion of prothombin to thrombin
- rare deficiency (antibiotic intake) -> hypoprothrombinemia in marginally malnourished individual
- ingle intramuscular dose of vitamin K as prophylaxis against hemorrhagic disease of the newborn
pg 898
20
Q
water soluble vitamins
A
all the B vitamins and vitamin C
- washed out from body except B12 and folate
- B12 stored in liver for 3-4 years
- folate stored in liver for 3-4 months
- can be co-enzymes (ascorbic acid) or precursor to co-enzymes (FAD, NAD+)
- all others need to be replenished daily
aside
* vitamin B4 (adenine), B8 (inositol), B10 (PABA), and B11 (salicylic acid) aren’t considered vitamins anymore and aren’t essential in diet
pg 901
