Niacin (Vitamin B3)

Question 1

Nicotinic acid formed from

Answer 1

Pyridine ring with carboxylic acid

Question 2

Niacinamide formed from

Answer 2

Pyradine ring with acid amide

Question 3

Alternate names for niacin

Answer 3

Nicotinamide
Vitamin B3

Question 4

Coenzyme form of niacin

Answer 4

NAD+ (Nicotinamide adenine dinucleotide)
NADP+ (Nicotinamide adenine dinucleotide phosphate)

Question 5

What is the role of NAD+ and NADP+ in metabolism?

Answer 5

NAD+ and NADP+: They are coenzymes for oxidoreductases (Hydrogen acceptors and donors)
They play very important roles in almost all metabolic pathways: Glycolysis, TCA cycle, ETC, Cholesterol metabolism, Fatty acid oxidation and synthesis

Question 6

RDA of niacin

Answer 6

15-20 mg

mg or NE (niacin equivalents)

Question 7

How is niacin synthesized?

Answer 7

Tryptophan and Vitamin B6

Tryptophan is also used in serotonin synthesis

Question 8

How much tryptophan is required for synthesis of 1mg niacin?

Answer 8

60mg tryptophan

Question 9

When is the requirement of niacin increased?

Answer 9

Pregnancy
Lactation
Chronic illness

Question 10

Sources of niacin?

Answer 10

Excellent sources: Yeast, fish, poultry, meats (high protein foods), liver
Good sources: Mushrooms, peanuts, fortified grain products

Question 11

How long do deficiency symptoms take to manifest?

Answer 11

After 45 days of depletion

Symptoms begin after coenzymes are degraded

Question 12

In what conditions may niacin deficiency be seen?

Answer 12

Poverty
Malnutrtion
Chronic alcoholism

Question 13

What are the signs and symptoms of niacin deficiency?

Answer 13

Mild deficiency: Superficial glossitis
Severe deficiency: Pellagra

Question 14

What are some symptoms of Pellagra?

Answer 14

DDD
Photosensitive Dermatitis - Sunburn like skin lesions in the areas of body exposed to sunlight as skin becomes red, itchy, blistered and cracked
Dementia: Memory loss, disorientation and personality changes
Diarrhea

Question 15

What are some nutritional causes of niacin deficiency?

Answer 15

Lack of vitamin B6
Lack of Tryptophan
Maize or corn or sorghum as staple diet: low bioavailability of niacin and less tryptophan

Question 16

What are some non-nutritional causes of niacin deficiency?

Answer 16

In Isoniazid therapy (for tuberculosis treatment): Causes B6 deficiency which results in blocking of conversion of Tryptophan to Niacin
Hartnups disease (genetic disorder): Failure of intestinal & renal tubular reabsorption of neutral amino acids
Carcinoid syndrome (metastasis of liver tumor of enterochromaffin cells): Tryptophan is utilized for synthesis of serotonin by the tumor

Question 17

What may niacin supplements be used to treat?

Answer 17

Niacin can be used therapeutically to lower plasma cholesterol & triglyceride levels (inhibits lipolysis in adipose tissue)
It has been used for chilblains (red round itchy swelling of the skin of fingers and toes in cold weather)

Question 18

What are the effects of excessive niacin intake?

Answer 18

High doses may cause blood vessels to dilate resulting in burning, tingling and red rash (flushing due to release of histamine)
Excess intake of nicotinic acid and nicotinamide (more than 500 mg/day) also cause liver damage

Question 19

How can activity of niacin be determined?

Answer 19

Red cell NAD concentration
Fasting plasma tryptophan