What is vitamin B3 composed of? Unpacking Niacin’s Chemical Structure

December 7, 2025 •

2 min read

Fact: The term vitamin B3, also known as niacin, is not a single compound but a collective name for several related molecules. Understanding what is vitamin B3 composed of reveals its fundamental chemical basis, which is essential for numerous metabolic processes in the human body.

Quick Summary

Vitamin B3 encompasses several related compounds, primarily nicotinic acid and nicotinamide, which serve as precursors for the coenzymes NAD and NADP, vital for energy metabolism. The body can also synthesize it from the amino acid tryptophan.

Key Points

Core Vitamers: Vitamin B3 is composed primarily of two molecules, nicotinic acid and nicotinamide, both based on a pyridine ring.
Active Coenzymes: In the body, these precursors are converted into the vital coenzymes Nicotinamide Adenine Dinucleotide (NAD) and Nicotinamide Adenine Dinucleotide Phosphate (NADP).
Endogenous Synthesis: The body can also produce niacin from the essential amino acid tryptophan, a process requiring other B vitamins and iron.
Metabolic Function: The coenzymes NAD and NADP are crucial for over 400 enzyme-catalyzed reactions, especially those related to energy metabolism, DNA repair, and cell signaling.
Structural Difference: The main chemical distinction between nicotinic acid and nicotinamide is the attachment of a carboxyl group versus a carboxamide group to the pyridine ring.
Niacin Flush: Nicotinic acid, unlike nicotinamide, can cause a harmless but uncomfortable skin flushing effect, especially in high doses.

The Primary Vitamers: Nicotinic Acid and Nicotinamide

Vitamin B3 primarily exists as nicotinic acid and nicotinamide, which are called vitamers. Both share a central pyridine ring structure. They differ in the chemical group attached at the third position of this ring.

Nicotinic Acid

Chemical Formula: C6H5NO2
Structure: Has a carboxyl group (-COOH) on the pyridine ring.
Use: Can lower cholesterol at high doses but may cause skin flushing.

Nicotinamide (Niacinamide)

Chemical Formula: C6H6N2O
Structure: Has a carboxamide group (-CONH2) on the pyridine ring.
Use: Used in supplements and does not typically cause flushing.

Beyond the Vitamers: The Coenzyme Forms

In the body, nicotinic acid and nicotinamide are converted into the active coenzymes NAD and NADP, which are vital for cellular functions.

NAD+ and NADP+: These are electron acceptors in metabolism. They include nicotinamide linked to a ribose sugar and an adenosine diphosphate (ADP) group.
NADP+ includes an extra phosphate group compared to NAD+, altering its role.
NADH and NADPH: These are the reduced forms, carrying electrons for building reactions.

The Body's Own Production Line: Tryptophan Conversion

The body can synthesize niacin in the liver from the amino acid tryptophan. This conversion is not very efficient, requiring about 60 mg of tryptophan per 1 mg of niacin and also needing sufficient riboflavin, pyridoxine, and iron.

Comparison of Niacin Vitamers


Feature	Nicotinic Acid	Nicotinamide	NAD/NADP
Core Structure	Pyridine ring + carboxyl group	Pyridine ring + carboxamide group	Nicotinamide + adenosine + phosphate groups
Pharmacological Use	Used in high doses to treat dyslipidemia by improving cholesterol levels.	Primarily for nutritional supplementation and treating deficiencies without causing flushing.	The active coenzyme forms are used for cellular redox reactions.
Side Effects	Can cause a “niacin flush,” characterized by redness, burning, and tingling.	Generally does not cause skin flushing when taken as a supplement.	High doses can cause liver toxicity; otherwise, side effects are from the precursor forms.
Primary Function	Precursor to NAD and NADP. Modulates lipid metabolism at high doses.	Precursor to NAD and NADP. Less impactful on lipid levels than nicotinic acid.	Coenzymes for over 400 enzymes involved in metabolic processes.

A List of Key Food Sources

To get enough niacin, include these foods in your diet:

Poultry: Good sources of niacin and tryptophan.
Fish: Excellent sources like tuna and salmon.
Red Meat: Provides niacin and tryptophan.
Legumes: Lentils and peanuts contain niacin and tryptophan.
Nuts and Seeds: Examples include peanuts and sunflower seeds.
Fortified Grains: Found in many breads and cereals.
Eggs and Dairy: Provide protein with tryptophan.

Conclusion

Vitamin B3 is a group of compounds, mainly nicotinic acid and nicotinamide, based on a pyridine ring. These are precursors to the essential coenzymes NAD and NADP, critical for energy metabolism and other processes. The body can also make niacin from tryptophan, though this is limited. This composition makes vitamin B3 vital for health. More information can be found on the Linus Pauling Institute website.

Frequently Asked Questions

The two main chemical forms of vitamin B3 are nicotinic acid and nicotinamide, which are both derived from a pyridine ring structure.

Yes, the human body can produce a small amount of niacin (vitamin B3) from the essential amino acid tryptophan in the liver.

NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate) are the active coenzyme forms that vitamin B3 is converted into inside the body.

The main chemical difference is that nicotinic acid has a carboxyl group (-COOH) attached to its pyridine ring, while nicotinamide has a carboxamide group (-CONH2).

The chemical formula for nicotinic acid is C6H5NO2.

The body's production of niacin from tryptophan is limited and depends on sufficient intake of tryptophan and other cofactors. For this reason, a dietary source of niacin is still considered essential.

The coenzyme forms NAD and NADP are the ones that participate directly in the hundreds of redox reactions necessary for energy production within cells.

As a water-soluble vitamin, any excess amount of niacin that the body does not need is simply excreted in the urine.