Niacin Deficiency Causes
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Questions and Answers

Why is niacin deficiency seen in people whose staple diet is maize?

  • Because maize contains leucine that inhibits the QPRT enzyme
  • Because niacin is present in a bound form and is unavailable (correct)
  • Because maize contains a toxin that destroys niacin
  • Because maize is poor in niacin

What is the enzyme that is inhibited by leucine in sorghum?

  • Tryptophanase
  • Pyridoxal phosphatase
  • Kynureninase
  • QPRT (correct)

Why does isoniazid (INH) lead to niacin deficiency?

  • It inhibits the absorption of niacin from the intestine
  • It inhibits the conversion of tryptophan to niacin
  • It increases the excretion of niacin in urine
  • It inhibits the formation of pyridoxal phosphate (correct)

What is the congenital disease characterized by defective tryptophan absorption and excretion in urine?

<p>Hartnup disease (C)</p> Signup and view all the answers

What is the richest natural source of niacin?

<p>All of the above (D)</p> Signup and view all the answers

How much of the daily niacin requirement is met by the conversion of tryptophan to niacin?

<p>About 50% (D)</p> Signup and view all the answers

What is the recommended daily allowance (RDA) of niacin?

<p>20 mg/day (D)</p> Signup and view all the answers

What is the effect of nicotinic acid on serum cholesterol levels?

<p>It decreases serum cholesterol levels (D)</p> Signup and view all the answers

Study Notes

Niacin Deficiency Causes

  • Dietary deficiency of Tryptophan leads to Pellagra, commonly seen in people whose staple diet is maize (South and Central America) or sorghum (Central and Western India)
  • Maize contains bound Niacin, making it unavailable, while sorghum's high Leucine content inhibits the QPRT enzyme, preventing Niacin conversion to NAD+
  • Deficient synthesis of Niacin occurs in Pyridoxal deficiency, as Kynureninase, an essential enzyme, is dependent on Pyridoxal phosphate
  • Isoniazid (INH), an anti-tuberculous drug, inhibits Pyridoxal phosphate formation, blocking Tryptophan to NAD+ conversion
  • Hartnup disease, a congenital disorder, impairs Tryptophan absorption and leads to excessive urinary excretion, resulting in Niacin deficiency
  • Carcinoid syndrome involves a tumor that utilizes most available Tryptophan for Serotonin synthesis, making it unavailable for Niacin production

Dietary Sources of Niacin

  • Richest natural sources of Niacin include dried yeast, rice polishing, liver, peanut, whole cereals, legumes, meat, and fish
  • About half of daily Niacin requirement is met through Tryptophan conversion to Niacin, with 60 mg of Tryptophan yielding 1 mg of Niacin
  • Normal daily requirement of Niacin is 20 mg/day
  • During lactation, an additional 5 mg/day is required

Therapeutic Use of Niacin

  • Nicotinic acid inhibits free fatty acid flux from adipose tissue, reducing serum cholesterol levels

Toxicity of Niacin

  • Oral or parenteral administration of Nicotinic acid causes transient vasodilatation of cutaneous vessels, accompanied by itching, burning, and tingling sensations
  • Excessive intake (over 50 mg/day) may lead to liver damage

Functions of Thiamine and Pyridoxine

  • Thiamine pyrophosphate is involved in carbohydrate metabolism
  • Pyridoxal phosphate is involved in protein metabolism

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Description

Learn about the causes of niacin deficiency, including dietary deficiency of tryptophan, pellagra, and the effects of leucine on niacin conversion.

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