Niacin Deficiency Causes

Questions and Answers

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

Tryptophanase

Pyridoxal phosphatase

Kynureninase

QPRT (correct)

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)

Hartnup disease Signup and view all the answers

All of the above Signup and view all the answers

About 50% Signup and view all the answers

20 mg/day Signup and view all the answers

It decreases serum cholesterol levels Signup and view all the answers

Study Notes

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

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

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

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