Niacin (Vitamin B3) Unit Converter
Niacin (Vitamin B3) Unit Converter
Convert niacin between mg/L, µg/L, ng/mL and µmol/L using nicotinic acid's molecular weight — with a note on why nicotinamide is a different molecule of nearly the same mass, and why niacin status is assessed on urine rather than plasma.
Niacin (Vitamin B3) converter
Mass ⇄ molarPlasma nicotinic acid 3 ng/mL
The conversion, and which molecule it belongs to
µg/L = ng/mL, and 1 mg/L = 1,000 µg/L
because 8.12282 = 1 mg/L ÷ 123.11 g/mol, the molecular weight of nicotinic acid
- MW 123.11 — nicotinic acid
- niacin proper, C₆H₅NO₂. This is the species the factor on this page is derived from
- MW 122.12 — nicotinamide
- the amide, C₆H₆N₂O. A different molecule, with a different pharmacology — it does not cause the flushing that nicotinic acid does and does not lower lipids — but a molecular weight only 0.8% lighter. A factor of 8.18886 rather than 8.12282, a difference too small to notice in a converted number and far too large to ignore when deciding which compound a report refers to
- µg/L = ng/mL
- identical concentrations. Plasma B3 is measured at single-digit ng/mL, which is why this page opens in that unit rather than in its base mg/L
- the tiny numbers
- a plasma nicotinic acid of 3 ng/mL is 0.024 µmol/L. The circulating concentrations are near the bottom of what an assay can resolve, which is one of several reasons the plasma level is a poor measure of status
Worked example
Plasma nicotinic acid 3 ng/mL
3 ng/mL = 3.00 µg/L = 0.0030 mg/L — the same concentration at three scales
0.0030 × 8.12282 = 0.024 µmol/L, or 24.4 nmol/L
Mayo report nicotinic acid in this panel as <5.0 ng/mL, so 3 ng/mL is an ordinary fasting figure — but that is a reporting limit, not a marker of adequacy
Convert with nicotinamide's 122.12 instead and you get 0.0246 µmol/L rather than 0.0244 — a 0.8% difference, invisible in practice
Which is the point: the conversion cannot tell you which molecule was measured, and the two behave completely differently in the patient. Read the report, not the number
What a laboratory actually reports for vitamin B3
| Analyte | Mayo VITB3 reference value | What it is |
|---|---|---|
| Nicotinic acid | <5.0 ng/mL | Niacin proper, MW 123.11 — the form that causes flushing and is used at gram doses for lipids |
| Nicotinamide | 5.0–48.0 ng/mL | The amide, MW 122.12 — the form in most supplements and fortified foods, and the direct precursor of NAD |
| Nicotinuric acid | <5.0 ng/mL | A conjugate of nicotinic acid with glycine, excreted in urine |
How niacin status is actually assessed
| Approach | What it measures | Standing |
|---|---|---|
| Urinary N¹-methylnicotinamide, usually with 2-pyridone | Excretion of the principal methylated metabolite, reflecting the size of the niacin pool being turned over | The established biochemical indicator of niacin status, and what the Dietary Reference Intakes were built on |
| Erythrocyte or whole-blood NAD, or the NAD:NADP ratio | The functional coenzyme pool | Used in research; falls before clinical signs appear |
| Plasma nicotinic acid or nicotinamide | Recent intake, at concentrations near the assay floor | Poor. Useful mainly for confirming exposure to a supplement or drug |
| Clinical assessment | Dermatitis in sun-exposed skin, diarrhoea, dementia — with the rash the most reliable sign | Pellagra is a clinical diagnosis, often confirmed by the response to treatment |
Two molecules, one mass, and a test that is rarely the answer
The conversion on this page is built from the molecular weight of nicotinic acid, 123.11 grams per mole, so one milligram per litre is 8.12282 micromoles per litre. Because plasma vitamin B3 circulates at single-digit nanograms per millilitre, the page opens in micrograms per litre — the same number as nanograms per millilitre, and the unit laboratories actually print — rather than in the milligrams per litre the factor is defined against.
The first thing worth knowing is that “niacin” names two compounds. Nicotinic acid, molecular weight 123.11, is the acid: the form that produces the prostaglandin-mediated cutaneous flush and the form used at gram doses as a lipid-modifying drug. Nicotinamide, molecular weight 122.12, is the amide: the form in most supplements and fortified foods, the direct precursor of nicotinamide adenine dinucleotide, and the form usually given to treat pellagra precisely because it does not flush. The masses differ by less than one per cent, so the two conversion factors — 8.12282 and 8.18886 — give answers that are indistinguishable in practice. That is a trap rather than a convenience: the arithmetic cannot tell you which molecule the report refers to, and the two compounds are not interchangeable clinically. Read the analyte name on the report.
The second thing is that the plasma level is a poor measure of niacin status, and this page prints no reference interval under the answer for that reason. Nicotinic acid circulates near the bottom of what the assay can resolve, concentrations move with the last meal, and the bulk of the body’s niacin is held as NAD and NADP inside cells rather than free in plasma. The indicator that nutrition science actually uses is urinary N¹-methylnicotinamide, usually reported with its 2-pyridone metabolite: it reflects the pool being turned over, and it is the measurement the Dietary Reference Intakes for niacin were derived from. Red-cell or whole-blood NAD is used in research and falls before clinical signs appear.
Pellagra itself is a clinical diagnosis. The textbook triad of dermatitis, diarrhoea and dementia is complete in a minority; the photosensitive rash over sun-exposed skin — the Casal necklace across the neck, and a symmetrical eruption on the backs of the hands — is the most reliable sign, and the response to treatment is often what confirms it. It is seen in chronic alcohol use, in malabsorption and carcinoid syndrome, in Hartnup disease, with isoniazid, and where maize is the dietary staple without the alkali treatment that liberates its bound niacin. None of that is decided by a plasma concentration.
Frequently asked questions
How do you convert niacin from mg/L to µmol/L?
Multiply by 8.12282, which is one milligram per litre divided by nicotinic acid’s molecular weight of 123.11 g/mol. Because plasma concentrations are measured in nanograms per millilitre, it is usually easier to work in µg/L: 1 µg/L is the same as 1 ng/mL, and 1,000 µg/L make 1 mg/L. A plasma nicotinic acid of 3 ng/mL is 0.024 µmol/L.
Is nicotinamide the same as nicotinic acid?
No. They are different molecules with nearly identical masses — 122.12 for nicotinamide against 123.11 for nicotinic acid — so their conversion factors differ by less than one per cent and a converted number cannot distinguish them. Clinically they differ a great deal: nicotinic acid causes flushing and lowers lipids at gram doses, while nicotinamide does neither and is the form usually used to treat pellagra.
Why does this page not show a reference interval for niacin?
Because a plasma niacin does not grade niacin status. Concentrations sit near the assay’s lower limit, move with the last meal, and say nothing about the intracellular NAD and NADP pools where almost all of the body’s niacin is held. Printing a normal range under the answer would imply a verdict the measurement cannot support. Mayo’s published values for their B3 panel are given in the table above for orientation.
What is the right test for niacin deficiency?
Urinary N¹-methylnicotinamide, usually reported with its 2-pyridone metabolite, is the established biochemical indicator and the one the Dietary Reference Intakes were built on. Erythrocyte or whole-blood NAD is used in research. In practice pellagra is diagnosed clinically — the photosensitive rash over sun-exposed skin is the most reliable sign — and often confirmed by the response to treatment.
Who develops pellagra today?
Chronic alcohol use is the commonest setting in high-income countries. It also occurs in malabsorption and after bariatric surgery, in carcinoid syndrome where tryptophan is diverted to serotonin, in Hartnup disease, with isoniazid, and where untreated maize is the dietary staple — maize niacin is bound and is only released by the alkali processing used traditionally in Central America.
Related calculators
References
- Mayo Clinic Laboratories. Test ID: VITB3 — Vitamin B3 and Metabolites, Plasma. Reference values: nicotinic acid <5.0 ng/mL, nicotinamide 5.0–48.0 ng/mL, nicotinuric acid <5.0 ng/mL.
- Institute of Medicine. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Washington DC: National Academies Press; 1998. Niacin chapter — urinary N¹-methylnicotinamide as the indicator of status.
- Hegyi J, Schwartz RA, Hegyi V. Pellagra: dermatitis, dementia, and diarrhea. Int J Dermatol. 2004;43(1):1–5.
- Jacobson EL, Jacobson MK. Tissue NAD as a biochemical measure of niacin status in humans. Methods Enzymol. 1997;280:221–230.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.