Vitamins And Cofactors Flashcards
Niacin (vitamin B3) requirements
17 mg men
13 mg women
Niacin (vitamin B3) food sources
- beef
- pork
- milk
- eggs
- now fortifying flour etc
Tryptophan is a precursor, so if getting a sufficiently high protein diet, niacin deficiency should not be an issue
Functions of niacin (vitamin B3)
- precursor for NAD
- can be synthesised in vivo from tryptophan
Consequences of niacin (vitamin B3) deficiency
- pellagra
- dermatitis, dementia, diarrhoea, death
Vitamin A requirements
- 7 mg men
0. 6 mg women
Vitamin A food sources
Preformed vitamin A
- liver
- meat
- milk
Provitamin Acarotenoids
- carrots
- broccoli
- oranges
Vitamin A functions
1) vision: all-trans- retinol enters the retinal pigment epithelium, and is isomerised to 11-cis-retinal. A photon of light is absorbed by the rod cells which isomerses back to all-trans-retinol. This isomerisation causes nerve impulse in optic nerve and light detection
2) gene transcription: all-trans-retinoic acid and 9-cis-retinoic acid are transported to the nucleus bound to cytoplasmic retinoic acid-binding proteins. Trans RA binds to RAR receptors, and cis RA binds to RXR receptors. These form hetereodimers which affect transcription
3) immunity: involved in maturation of WBC and activation of T lymphocytes
4) growth and embryonic development (too much can also cause deformation)
Consequences of vitamin A deficiency
- higher incidences of childhood illnesses eg. Measles
- birth defects
Vitamin C requirements
40 mg
Vitamin C food sources
- citrus fruits
- red pepper
- broccoli
- potato
Functions of vitamin C
- synthesis of collagen
- synthesis of neurotransmitter norepiniehrine
- synthesis of carnitine for fatty acid metabolism
- antioxidant
- regenerate antioxidants such as vitamin E
Vitamin C deficiency
- scurvy
- collagen synthesis issues, pale skin, sunken eyes, loss of teeth
- bleeding and bruising easily
- joint pain and swelling
- scurvy corkskrew hairs
Vitamin B12 requirements
0.0015 mg
Sources of B12
- dairy
- meat
- fortified yeast
Functions of B12
- coalbumin is a cofactor for 2 enzymes: methioine synthase, L-methylmalonyl-CoAmutase
- methionine synthase: required for amino acid methionine from homocysteine. Methionine is used for the synthesis of S-adenosylmethionine which is involved in methylation (epigenetic) of DNA/RNA
- L-methylmalonyl-CoAmutase: converts L-methylmalonyl-CoA to succinyl CoA which is required for the synthesis of haemoglobin, and this reaction is important in the production of energy from fats and protein
B12 deficiency
- elevated homocysteine levels, increased MMA
- neurologic symptoms
- subacute combined degeneration fo the cord: numbness and tingling in arms and legs
- dementia, difficulty walking
Causes: not including enough in diet, pernicious anaemia
Thiamine (vitamin B1) requirements
1 mg men
0.8 mg women
Thiamine (vitamin B1) food sources
- wholegrains
- peas
- vegetables
- milk
- cheese
Thiamine (vitamin B1) functions
- coenzyme for 2 reactions in TCA cycle (participates is resonance stabilisation): pyruvate dehydrogenase, a-ketoglutarate dehydrogenase
- coenzyme in pentose phosphate pathway: transketolase
- involved in electrical conduction in nerve cells: thiamin triphosphate phosphorylates and activates chloride channels in nerve membranes
Thiamine (vitamin B1) deficiency
- beriberi
- those most at risk: narcotics users, alcoholics, HIV/AIDS patients
- wet beriberi (severe deficiency, higher carbohydrate and physical activity): CV consequences, oedema, heart failure, pain, death
- dry beriberi (prolonged and less severe deficiency): loss of sensation in hands and feet, pain, muscle damage/paralysis, death
Thiamine (vitamin B1) deficiency: Wernicke’s encephalopathy. Risk factors, symptoms, impact, treatment
- risk: alcoholics (reduced absorption and poor diet), cancer pts, starvation, CKD, IV CHO loading
- symptoms: neuropsychiatric, delerium tremens, loss of memory. Only 10% have symptoms though
- impact: B1 used in the PPP, glycolysis and the TCA cycle as a coenzyme. Reduction in these can reduce myelin sheath formation and ATP production in the brain
- treatment: PABRINEX B-vitamin complex IV
Types of radicals and radical damage
- can cause peroxidation of plasma lipoproteins of unsaturated fats causing reactive dialdehydes to form which can cause below problems
- damage to DNA causing heritable (germ line) and somatic (cancerous) mutations
- damage to amino acids in proteins, causing antibodies to be raised (basis of autoimmune disease)
- modification to LDL (oxidation) cause engulfing by macrophages and beginning of atherosclerosis
Vitamin C antioxidant functions
- regenerates tocopherol (vitamin E) when reacted with radical
- can react directly with radicals to form monodehydroascorbate
- however, in high doses can also form free radicals with oxygen and Cu
Proposed benefits and drawbacks of vitamin C
- reduces cold longevity by 0.5 days
- reduced risk of breast cancer
- reduced stroke risk, but no evidence that supplementation improves further
- increases CHD risk in post-menopausal diabetic women
- increased all-cause mortality
- causes kidney/ bladder stones
Protection against free radical damage
- superoxide dismutase
- catalase
- Fe: transferrin
- Cu: ceruloplasmin
- metallothionien
- glutathione peroxidase (Se containing enzyme) reduces lipid peroxides
Antioxidant functions of vitamin E (tocopherol)
- forms stable tocopherol radical with lipid peroxides, regenerates by ascorbate
Proposed benefits and drawbacks of vitamin E
- in epidemiological studies show reduced CHD risk
- antioxidant
- increased chance of fatal myocardial infarction, and increased total mortality
- pro-oxidant effect
Beta- carotene antioxidant effect
Conjugated double bond system reacts with radicals to form stable complex
Proposed benefits and drawbacks of beta- carotene
- epidemiological studies show lower cancer mortality with higher serum beta- carotene
- in lower than atmospheric pO2 (in tissues) is anti-carcinogenic
- in higher pO2 is a pro-oxidant i.e in the lungs, therefore increases lung cancer risk in smokers
