Micronutrients II - Vitamins Flashcards
Which vitamins are most utilized in energy metabolism?
B vitamins
Vitamins
typically cofactors for enzymes
organic compounds required for diet in only small amounts to maintain fundamental cell functions
not catabolized
Organic
how many water soluble vitamins?
9
how many lipid soluble vitamins?
4
Vitamin-like compounds
Inositol
Choline
Lipoic Acid
PQQ-Pyrroloquinoline quinone
Inositol
phospholipids
Choline
in phospholipids, methyl donor
choline free diet could lead to liver damage
Lipoic Acid
not a vitamin but required for pyruvate decarboxylase
animals can make this
PQQ-pyrroloquinoline quinone
methoxatin
redox cofactor for quinoproteins
ex: flavoproteins - dehydrogenases
Vitamin D only needed when
sunlight is absent
Primary deficiency
lack of adequate intake in diet
causes of Primary deficiency
poor nutrition/food habits, poverty, ignorance of nutrition needs, insufficient food, lack of proper vitamin rich foods, food fads, food taboos, vitamin destruction, anorexia
Secondary deficiency
poor availability or utilization of a vitamin due to environmental or physiological conditions
Causes of secondary deficiency
poor digestions (achlorhydria-low gastric acid) malabsorption (diarrhea, infections) impaired utilization (drug therapy)
Vitamin deficiencies significant in
any pt with digestion/malabsorption problems
chronic substance abuse (alcohol) bad diet & inhibits uptake of vit
recent surgery, total parenteral nutrition
elderly, pregnant/breastfeeding, smokers, alcoholics, diabetics
risk thiamine deficiency with high CHO diet
What aids in fat soluble vitamin absorption?
Bile
digestive enzymes from pancreas help uptake
vitamin K
Bacteria in the gut make small amount of
vitamin K, B12, and biotin
Fat soluble vitamins are absorbed with
dietary fat
where are fat soluble vitamins stored?
liver and nonspecifically adipose tissue
Risk of toxicity with what vitamin?
B vitamins
Vitamin A
mixture of Retinoids
role in gene regulation - reproduction, embryogenesis, development, cell differentiation and proliferation) vision, maintenance of brain function and skin
Vitamin A deficiency
night blindness
hyperkeratosis
Vitamin A Excess
birth defects, (tetratogenic), blurred vision, liver damage
Osteoporosis, hypercalcemia
Vitamin A is derived from
carotenoids
plant pigments
b-carotene
-three forms - alcohol, aldehyde and acid
Find Vitamin A in
green, leafy vegetables
colored veggies
organ meat - liver
Why is beta carotene a safer source?
conversion to Vit A in gut decreases as dose increases
Absorption depends on type of food and how much fat is also in diet
How is Vitamin A taken up?
Retinol and carotenoids bound in enterocyte to Carotene binding proteins
carried in blood by chylomicrons or albumin
How is vitamin A important for vision?
combines with opsin to form rhodoposin in rod and cone cells
impt for the shape and structure of the conjunctiva and the cornea as well
functions in cellular differentiation - RXR and RAR receptors
Xerophthalmia
damage to cornea
can occur with vitamin A deficiency
Accutane
oral vitamin A treatment for acne
not for pts who can get pregnant
causes birth defects
Excess Vitamin A
headache nausea skin irritation pain in joints Osteoporosis
RAE
retinol activity units
Vitamin A RDA
men - 900ug/day
women - 700ug/day
what are some world wide problems seen with Vitamin A deficiencies?
increased susceptibility to infection
blinds nearly 500,000 preschool aged children
worsens iron status, causing anemia
accompanies protein and Zinc malnutrition
chronic fat malabsorption, low fat intake
Rickets
in children
severe bone deforming disease from lack of Vitamin D
cured with sunlight/fish oil
Vitamin D
mixture of ergocalciferol (D2) and cholecalciferol (D3)
derived from cholesterol - synthesized in the skin
What is active form?
Calcitrol (1,25-dihyroxyvitamin D
liver converts D3 to 25-hydroxyvitamin D
then kidneys converts to 1,25-dihyroxyvitamin D
Function of Vitamin D
regulates Ca levels in body
increases Ca uptake from diet, decreases Ca loss in uring , facilitates release of Ca from bones
may also modulate inflammation/immune responses
Osteomalacia
Vit D deficiency in adults
Vitamin D RDA
10ug/day (about 2 liters of vit D fortified milk
Vitamin D excess
large excess can be lethal
leads to hypercalcemia - deposition of Ca in soft tissues)
there can be local tissue intoxication
Vitamin D deficiencies linked to
Type II diabetes, autoimmune disease and other chronic diseases - cardiovascular, cancer
Serum level of Vit D deficiency
less than 20 ng/mL
Vitamin K
group of 3 molecules
phylloquinones
k1 - phllyoquinone in green leafy veggies
k2 - menaquinone, made by bacteria in intestines
k3 - menadione, artificial
Functions of Vitamin K
required for post-translational modification of many proteins which bind Ca++ including blood coagulating proteins
cofactor for carboxylases which add gamma-carboxy group onto glutamates
vitamin K inhibitors
coumarin/warfarin
inhibit clotting
Coumarin
in low doses inhibits vitamin k epoxide reductase and vit K reductase
so depletes Vit K and inhibits enzymes requiring vit K
all these inhibited activities lead to blood clotting
Name the B vitamins
Thiamine (b1) Riboflavin (b2) Niacin (b3) Pantothenic acid (B5) Pyridoxine (pyridoxal, pyridoxamine) (b6) Biotin (vitamin H) Cobalamin (b12) Folic acid
Thiamine functions
helps form/break C-C bonds
- Oxidative decarboxylation - pyruvate and a-ketoglutarate DH
- Transketolase in PPP - converts glucose to ribose for DNA synthesis
Thiamine deficiency
Beriberi Insufficient ATP production, decreased synthesis of DNA, RNA, proteins, fatty acids muscle tissue wasting cardiovascular damage CNS damage - confusion, loss of reflex Edema seen in chronic alcoholism usually see in skin first
Wernicke syndrome
Thiamine deficiency
associated with chronic alcoholism
known as dry beriberi becomes wet when develop cardiac dilated hypermyopathy (loss of energy, fluid build up)
Severe Thiamine deficiency leads to
involves CNS
called Korsakoff encephalopathy (Wernicke-korsakoff syndrome) - leads to short term memory loss
irreversible
What predisposes people to WK syndrome when diet is thiamine deficient ?
mutation in transketolase
Riboflavin
heat stable but light sensitive intense yellow-green fluorescence Coenzyme in TCA cycle - FAD/FADH cofactor for other enzymes, oxygenases, oxidoreductases can carry 2 electrons can store about 1-2 weeks worth
what inhibits Thiamine uptake?
Alcohol
Riboflavin deficiency
prolonged can lead to cracked lips, dark red tongue, dermatitis, normocytic anemia, confusion
Excess Riboflavin
no real effect
lost rapidly
Forms of Niacin
nicotinic acid (precursor to NAD and NADP) and nicotinamide Active form is NAD (bound to ribose and ADP)
Niacin deficiency
Pellagra -fragile skin called Casal’s necklace
corn is low in niacin and Trp
fatigue, headache, apathy, depression, memory loss, dementia, pigmented skin rash after sun exposure, vomiting, diarrhea
Trp metabolite in urine suggests deficiency in
Niacin
Niacin Equivalents NE
1 mg pure niacin or 60 mg trytophan
Men 16 mg NE/day
women 14
Hartnup disease
impairs Trp absorption can lead to niacin deficiency
Excess Niacin
Flushing, buring of face, arms and chest, stomach irritation
long term - liver damage, irreversible liver failure
Excess of what vitamin could be cholesterol lowering ?
Niacin
must be watched carefully though
acts via G protein coupled receptor, reduces lipolysis, free fatty acids, VLDLs
Pantothenic acid
component of CoA and acyl carrier protein
No RDA, no deficiencies, excess seen
hard to differentiate Pantothenate deficiency from other vit B deficiencies - skin problems, burning feet, digestive problems, dizziness
Pyridoxine
involved in transamination, decarboxylation
required for function of glycogen phosphorylase, synthesis of heme, y-aminobutyric acid
Pyridoxal Phosphate (PLP)
derived from B6
deficiency leads to dermatitis and disorders of protein metabolism
group for enzymes catalyzing reactions involving amino acid metabolism
Pyridoxine deficiencies
microcytic anemia, EEG abnormalites, epileptic seizures, depression, confusion, seborrheic dermatitis, maybe also platelet and clotting problems
Drugs that can create a PLP deficiency
penicillinamine or isozianid
Pyridoxine excess
peripheral neuropathy, derm lesions
Biotin
synthesized by gut bacteria
tightly binds to egg protein (avidin)
functions in carboxylase reactions in FA synthesis, essential for lipid metabolism, amino acid breakdown
Biotin deficiency
impaired glucose tolerance, mental dysfunction, nausea, anorexia, dermatitis
some anticonvulsants inhibit uptake
Cyanocobalamin - vit B12
conenzymes: methylcobalamin, adenosylcobalamin
most potent - 3ug/day
contains corrin ring system and a cobalt
only synthesized by some bacteria
participates in enzyme catalyzed molecular rearrangements, ribonucleotide reductase and methyl group transfers
regenerates FH4 from methyl folate, prevents folate deficiency
Vitamin B12 deficiency
- can cause long tern, permanent damage to myelin sheath, peripheral neuropathy
- Pernicious anemia - megaloblastic anemia due to lack of intrinsic factor secretion
- lead to elevated homocysteine levels which are linked to CVD due to interference with collagen maturation
B12 and folate
intimate interaction with folate
levels fall with folate
anemia, temporarily respond to folate tx masking the deficiency but has neuro consequences
B12 deficiency most common in
wealthier countries, among elderly, most prevalent in poorer populations
Metformin
impairs B12 uptake
Diagnosis of B12 deficiency
serum or plasma ~200 pg/ml
Excess B12
doesnt hurt
what deficiencies increase serum tHcy
folate riboflavin vitamin B6 B12 THF
Homocysteine
remove terminal Ch3 from methionine
conversion of homocysteine to Methionine
Tetrahydrofolate and B12
conversion of homocysteine to Cys
B6
Intrinsic Factor
secreted from parietal cells in response to hormone
B12 ONLY absorbed in intestines when complexed to IF
binds to specific receptor in the ileum
Pernicious anemia
megaloblastic anemia due to lack of intrinsic factor secretion
atrophy of mucosa, loss of secretion of gastric acid and IF
Liver stores B12 can last
6-10years
Folate
FH4 made from folate
major carrier of single carbon units
takes 1C from Ser, Gly, His, formaldehyde and formate
1C transferred to pyrimidine dUMP to form dTMP - vital for DNA synthesis
cooking destroys 90% in food
Folate deficiency
affects rapidly dividing cells - RBC, intestinal epithelium, fetal tissues
Fetal - neural tube defects
Megaloblastic anemia
caused by both folate and cobalamine deficiencies
due to thymidylate synthase deficiency
causes enlarged red and white blood cells - abnormal nuclear maturation - NOT enough DNA
oral contraceptives and anticonvulsants
impair absorption or increase the breakdown of folate
Single carbon transfers
THF transfers CH3 to B12 which adds that too Homocysteine to make methionine
Vitamins stored in the liver
B12
Folate
