Vitamin B3 - Niacin Flashcards

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1
Q

List dietary sources of niacin

A

Fish and meats
Riches flours, fortified cereals, whole grains, seeds and legumes
Coffee and tea
Green leafy vegetables
Dairy products
Also synthesized in the liver from tryptophan
- takes 60mg of tryptophan to produce 1mg of niacin
- riboflavin, B6 and iron are required for conversion

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2
Q

Describe the digestion niacin

A

In animals niacin mainly occurs as NAD & NADP but after slaughter it undergoes hydrolysis to free nicotinamide

NAD & NADP are also hydrolyzed to free nicotinamide in the intestinal tract

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3
Q

Describe the absorption of niacin

A

Nicotinamide and niacin are absorbed in:
Stomach - minor - enhanced by HCL
Small intestine - major

Two mechanisms

  1. Sodium dependent carrier-mediated diffusion
  2. Passive diffusion

*can also be absorbed through the skin - creams

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4
Q

Describe the transport of niacin

A

Transported in The Lord primarily as free nicotinamide

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5
Q

Describe the function and mechanism of action of niacin

A

Over 200 enzymes use NAD or NADP as coenzymes
NAD used in:
- glycolysis
- oxidation of acetyl CoA, FAs & ETOH
NADH transports electrons through intermediates in ETC
NADPH required in:
- synthesis of FAs, cholesterol, steroid hormones, deoxyribonucleotides
- regeneration of glutathione and vitamin C
- conversion of folate to its active form
To detoxify alcohol

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6
Q

Describe the metabolism and excretion of niacin

A

NAD/NADP is degraded into nicotinamide which is then methylated and oxidized in the liver to several metabolites that are excreted in the urine

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7
Q

Describe consequences and symptoms of deficiency of niacin

A

Pellagra
Symptoms:
Dermatitis
- appears on areas exposed to sun a s similar to sunburn at first
Dementia and other neurological manifestations
- H/A, apathy, anxiety, loss of memory, peripheral neuropathy and paralysis of extremities
Diarrhea and other GI manifestations
- glossitis, cheilosis/stomatitis, nausea, vomiting and constipation
Death

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8
Q

Who are at increase risk of developing a niacin deficiency?

A

Alcoholic
Elderly in nursing homes
Low income
Carcinoid syndrome –> tumor cells have increased production of serotonin
Hartnup’s disease –> impaired tryptophan absorption
The use of certain medications, such as anticonvulsants and isoniazid

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9
Q

Describe consequences and symptoms of toxicity of niacin

A

UL = 35mg/d

Side effects seen with doses >1g/d

  • vasodilatory effects: flushing, redness, burning, itching, tingling, h/a
  • GI effects: acid reflux, nausea, vomiting, loss of appetite in children
  • hepatotoxicity:
    • obstructive jaundice, hepatitis, liver failure
    • monitor LFTs (liver function tests)
    • liver function reruns to normal after discontinuation
    • sustained release preparations are more hepatotoxic
  • hyperurecemia and gout
  • hyperglycemia/hypoglycemia

Flush may be reduced by:

  • taking 80-500mg of aspirin (will still feel itchy)
  • taking an antihistamine
  • taking nicotinamide acid after a meal
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10
Q

Describe the assessment of nutrient status of niacin

A

Measuring urinary metabolites
Erythrocyte NAD concentration
Ratio of NAD to NADPH
Clinical response to supplementation

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11
Q

Discuss some of the therapeutic uses (clinical indications) of niacin

A
Hyperlipidemia
- nicotinamide acid 1-6g/d
- shown to lower TC, TGs, LDL, and increase HDL
Anxiety disorders
- nicotinamide 1.5-6g/d

Best taken in divided doses due to short half life and to reduce side effects

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