From niacin to NAD+
Vitamin B3 exists mainly as niacin (nicotinic acid) and nicotinamide, and both serve as precursors to NAD+ (nicotinamide adenine dinucleotide) and its phosphorylated partner NADP+. These coenzymes carry electrons in hundreds of redox reactions, including the energy-releasing steps of glycolysis, the citric acid cycle, and oxidative phosphorylation. NAD+ is also consumed by enzymes such as sirtuins and PARPs involved in DNA repair and signalling.
The body can also make some NAD+ from the amino acid tryptophan, which is why severe deficiency usually requires both low niacin and low protein intake. The diagram traces the conversion from dietary B3 to the NAD+ pool.
Pellagra and the difference between the forms
Classic niacin deficiency is pellagra, remembered by the three Ds: dermatitis (notably on sun-exposed skin), diarrhoea, and dementia, progressing to death if untreated. It is now rare where diets are varied. The two forms differ in side effects: high-dose nicotinic acid causes the well-known flushing reaction and has been used pharmacologically for cholesterol, while nicotinamide does not flush.
High-dose niacin can affect the liver and blood sugar and is a medical intervention, not a casual supplement. This is general educational information, not medical advice; use therapeutic niacin doses only under a qualified professional.