Chemical Identity and Forms
Vitamin B3 exists in two primary forms that serve as vitamers:
- Nicotinic acid (niacin) - the acid form of vitamin B3 3, 4
- Nicotinamide (niacinamide) - the amide form of vitamin B3 3, 4
Both forms are converted in the body to the active coenzyme forms NAD+ (nicotinamide adenine dinucleotide) and NADP+ (nicotinamide adenine dinucleotide phosphate), which are essential for over 400 enzymatic reactions involving energy metabolism, DNA repair, and cellular signaling. 1, 5, 6
Historical Context
Vitamin B3 earned its designation as the "third B vitamin" because it was the third vitamin to be discovered historically. 4 The term "vitamin PP" (pellagra-preventive) was also used historically, as niacin deficiency causes pellagra. 4
Key Distinction Between the Two Forms
While both nicotinic acid and nicotinamide function as vitamin B3, they have markedly different pharmacological properties:
- Nicotinic acid causes flushing at doses as low as 30 mg due to activation of the GPR109A receptor 2, 5
- Nicotinamide does not cause flushing and does not activate GPR109A, despite having equivalent vitamin activity 2, 7, 3
This distinction is clinically important when prescribing therapeutic doses, as the upper safety limit for free nicotinic acid is only 10 mg/day (due to flushing), whereas nicotinamide can be safely used at approximately 900 mg/day for adults. 2, 5