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fundamentals of nutrition and metabolism > Vitamins And Cofactors > Flashcards

Vitamins And Cofactors Flashcards

1
Q

Niacin (vitamin B3) requirements

A

17 mg men

13 mg women

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2
Q

Niacin (vitamin B3) food sources

A
  • 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

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3
Q

Functions of niacin (vitamin B3)

A
  • precursor for NAD

- can be synthesised in vivo from tryptophan

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4
Q

Consequences of niacin (vitamin B3) deficiency

A
  • pellagra

- dermatitis, dementia, diarrhoea, death

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5
Q

Vitamin A requirements

A
  1. 7 mg men

0. 6 mg women

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6
Q

Vitamin A food sources

A

Preformed vitamin A

  • liver
  • meat
  • milk

Provitamin Acarotenoids

  • carrots
  • broccoli
  • oranges
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7
Q

Vitamin A functions

A

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)

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8
Q

Consequences of vitamin A deficiency

A
  • higher incidences of childhood illnesses eg. Measles

- birth defects

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9
Q

Vitamin C requirements

A

40 mg

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10
Q

Vitamin C food sources

A
  • citrus fruits
  • red pepper
  • broccoli
  • potato
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11
Q

Functions of vitamin C

A
  • synthesis of collagen
  • synthesis of neurotransmitter norepiniehrine
  • synthesis of carnitine for fatty acid metabolism
  • antioxidant
  • regenerate antioxidants such as vitamin E
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12
Q

Vitamin C deficiency

A
  • scurvy
  • collagen synthesis issues, pale skin, sunken eyes, loss of teeth
  • bleeding and bruising easily
  • joint pain and swelling
  • scurvy corkskrew hairs
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13
Q

Vitamin B12 requirements

A

0.0015 mg

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14
Q

Sources of B12

A
  • dairy
  • meat
  • fortified yeast
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15
Q

Functions of B12

A
  • 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
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16
Q

B12 deficiency

A
  • 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

17
Q

Thiamine (vitamin B1) requirements

A

1 mg men

0.8 mg women

18
Q

Thiamine (vitamin B1) food sources

A
  • wholegrains
  • peas
  • vegetables
  • milk
  • cheese
19
Q

Thiamine (vitamin B1) functions

A
  • 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
20
Q

Thiamine (vitamin B1) deficiency

A
  • 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
21
Q

Thiamine (vitamin B1) deficiency: Wernicke’s encephalopathy. Risk factors, symptoms, impact, treatment

A
  • 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
22
Q

Types of radicals and radical damage

A
  • 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
23
Q

Vitamin C antioxidant functions

A
  • 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
24
Q

Proposed benefits and drawbacks of vitamin C

A
  • 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
25
Q

Protection against free radical damage

A
  • superoxide dismutase
  • catalase
  • Fe: transferrin
  • Cu: ceruloplasmin
  • metallothionien
  • glutathione peroxidase (Se containing enzyme) reduces lipid peroxides
26
Q

Antioxidant functions of vitamin E (tocopherol)

A
  • forms stable tocopherol radical with lipid peroxides, regenerates by ascorbate
27
Q

Proposed benefits and drawbacks of vitamin E

A
  • in epidemiological studies show reduced CHD risk
  • antioxidant
  • increased chance of fatal myocardial infarction, and increased total mortality
  • pro-oxidant effect
28
Q

Beta- carotene antioxidant effect

A

Conjugated double bond system reacts with radicals to form stable complex

29
Q

Proposed benefits and drawbacks of beta- carotene

A
  • 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

fundamentals of nutrition and metabolism (12 decks)

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