Principles of Biochemistry (2+1)

10.1.3 Niacin

Niacin or Nicotinic acid is pyridine 3-carboxylic acid. It occurs in tissues as niacinamide (nicotinamide). It is stable to heat and not destroyed by autoclaving at 120°C for 20min. in alkaline or acid medium.Nicotinamide Adenine Dinucleotide (NAD+) and Nicotinamide Adenine Dinucleotide Phosphate (NADP+) are the coenzymes of niacin.

Functions: NAD⁺ (Nicotnamide adenine dinucleotide) and NADP⁺ (Nicotnamide adenine dinucleotide phosphate) are coenzymes for many oxidoreductase enzymes. The nicotinamide nucleotides play a widespread role as coenzymes to many dehydrogenase enzymes occurring both in the cytosol (e.g. lactate dehydrogenase) and within the mitochondria (e.g. malate dehydrogenase). They are therefore key components of many metabolic pathways affecting carbohydrate, lipid, and amino acid metabolism. Generally NAD-linked dehydrogenases catalyze oxidoreduction reactions in oxidative pathways (eg, the citric acid cycle), whereas NADP-linked dehydrogenases or reductases are found in pathways concerned with reductive syntheses (e.g. the pentose phosphate pathway).

Deficiency Lack of niacin causes the deficiency syndrome Pellagra. Symptoms include weight loss, three Ds: diarrhea, dermatitis and dementia. Pyridoxal phosphate, the active form of vitamin B6, is involved as a cofactor in the pathway of synthesis of NAD⁺ from tryptophan and vitamin B6, deficiency can therefore potentiate a deficiency in niacin.

RDA

 Infants :5- 8mg

 Children :9-16mg

 Adult (male) :16-20mg

 Adult (female) :12-16mg

 Pregnant women :14-18mg

 Lactating women :16-20mg 

Sources 

Niacin is found widely in most animal and plant foods.

 

Good sources : Meat, liver and poultry

Fair sources : fish, eggs, milk, tomatoes, green leafy vegetable.