Introduction, Structure, Coenzymes, Sources, RDA, biosynthesis, Metabolism, Functions, Deficiency and toxicity manifestations.

1. NIACIN – Vitamin B3
-Suriya Prabhu A R
-132, M.B.B.S- I, TMCH.

2. INTRODUCTION
• Niacin is the generic term for nicotinamide and nicotinic
acid.
• Also known as Niacinamide / Nicotinamide / Vitamin PP
(pellagra preventive) / Vitamin G (after Goldberger).
• is an organic compound with the formula C6H5NO2
• Simple derivative of pyridine.
• Pyridine 3 carboxylic acid.
• White crystalline substance.
• Water soluble.
• Resistant to heat, oxidation & alkalis.
• Nicotinamide is an important component of NAD and
NADP.

3. STRUCTURE
• Niacin has a carboxyl group (COOH) at the 3-position, whereas,
in Nicotinamide the carboxyl group is replaced by a
Carboxamide group (CONH2) .

6. RECOMMENDED DAILY ALLOWANCE FOR
VITAMIN B3
*During Pregnancy 18 mg; during Lactation 17 mg.

7. ENDOGENOUS SYNTHESIS
• Liver can synthesize Niacin from essential amino acid
Tryptophan, requiring 60 mg of Tryptophan to make
1 mg of Niacin.

9. FUNCTIONS
• Niacin is required by all cells. It plays a vital role in the
release of energy from all energy giving nutrients-
Carbohydrates, fat, protein, alcohol.
• Also required for the synthesis of protein, fat & 5C sugars
needed for the formation of DNA & RNA.
• The biochemical role of niacin is to form part of coenzymes
NAD & NADP require by many of the key pathways of the
metabolism.
• Coenzymes NAD and NADPH are electron carriers of cells.
NAD is primarily involve in catabolic reactions whereas,
NADP functions mainly in anabolic reactions. They are
coenzymes for more than 200 enzymes reactions.

10. • Some reactions where niacin in the form of NAD is involved are :
• 1. Conversion of lactate to pyruvate in glycolytic pathway.
• 2. Glyceradehyde-3-PO4 to 1, 3 biphosphoglycerate in glycolytic
pathway.
• 3. In biological oxidation reduction complex.
• 4. α- ketoglutarate to succinyl CoA in TCA cycle.
• 5. Malate to oxaloactetate in TCA cycle.
• Niacin in the form of NADP is involved in the following:
• 1. Glucose-6-PO4 to 6-Phospho gluconolactone in HMP shunt.
• 2. 6-phospho gluconate to 3 keto-6 phosphogluconate in HMP shunt.
• Thus they play an important role in mechanisms for DNA repair and
gene stability and therefore influence cancer risk.

11. DEFICIENCY OF NIACIN (Vit. B3)
Symptoms caused by Dietary deficiency of
Tryptophan and/or Deficiency in Synthesis:
 Early Manifestations
Anorexia, Weight loss, Irritability, Weakness
 Later stages result in Pellagra
Commonly referred to as the 4 D’s
1. Dermatitis
2. Dementia
3. Diarrhea
4. Death (if not treated)

12. • Dermatitis
Inflammation of skin areas exposed to the sunlight
Arms, legs, V of neck
Oral Manifestations: Oral mucosa is red and painful ; Epithelium of
entire tongue is desquamated ; Tongue becomes red, swollen ;
Gingivitis.
Increased pigmentation
around neck known as
Casal’s Necklace

13. • Diarrhea
Gastrointestinal system is disturbed ;
Leading to mild to severe Diarrhea ;
Leads to weight loss, Nausea and Vomiting,
Abdominal discomfort.
• Dementia
Central nervous system is affected ;
Confusion, Memory loss,
Dizziness, Hallucinations, Insomnia.

14. NIACIN TOXICITY
• Large doses of nicotinic acid (up to 6 g/day in divided
doses) are used to treat hypercholesterolemia (high
blood cholesterol).
• Large doses 150-300mg oral and 20mg intravenous
results in:
• Vasodilation; Painful flush, Hives, Rash
• Histamine release
• Excessive sweating; Blurred Vision; Liver damage;
Impaired Glucose Tolerance.

15. Thank you.
Thanking the Department of Bio-Chemistry for this opportunity.
Thanks to Coffee for helping me do this.