Vitamin B3 (niacin)
Water-soluble B vitamin for energy metabolism, skin, nerves and digestion
Also known as
Definition
Vitamin B3 (niacin, as nicotinic acid or nicotinamide) is a water-soluble B vitamin. It helps turn food into energy and supports digestion, skin and nerves. The body keeps only a small reserve, and excess amounts leave in the urine. Niacin is found in foods such as milk, eggs, fish, lean meat, poultry, legumes, peanuts and enriched grains. It is measured as part of a vitamin B test in blood or urine.
| Parameter | Value |
|---|---|
| Unit | varies by lab and method |
| Reference Range | No uniform reference range: for some B vitamins it is not clear what a normal level is, and labs use different ranges. The reference range on your own report is what counts; discuss it with your doctor. |
Agree on your personal target range with your doctor.
↓ What a low value means
Severe niacin deficiency causes pellagra, which can come with digestive problems, inflamed skin and impaired mental function. Low B vitamin levels can be linked to alcohol use disorder, celiac disease, Crohn's disease, other malabsorption conditions, surgery on the digestive tract, a diet low in animal foods or certain medicines. Inflammation and medicines can affect the values; discuss your result with your doctor.
↑ What a high value means
High niacin levels can come from supplements. Too much niacin can raise blood sugar, damage the liver and come with peptic ulcers and skin rashes. Nicotinic acid can also cause flushing: warmth, redness, itching or tingling of the face, neck, arms or upper chest. At high doses niacin also changes blood lipids (HDL rises slightly, triglycerides fall). High B vitamin levels can also be linked to conditions such as liver disease; discuss any deviation with your doctor.
When to test
A vitamin B test is mainly ordered for symptoms that suggest a deficiency or for risk factors such as malabsorption, alcohol use disorder or surgery on the digestive tract. It is measured in blood or urine (random sample or 24-hour collection). Fasting may be needed before a blood sample. Mention supplements and medicines before the blood draw.
Frequently asked questions
What is the difference between nicotinic acid and nicotinamide? +
Both are forms of vitamin B3. The typical flushing with warmth, redness and tingling is described for nicotinic acid; supplements containing nicotinamide (niacinamide) do not appear to cause this side effect. The label tells you which form a product contains.
Can niacin change other lab values? +
Yes. High doses can raise HDL cholesterol slightly and lower triglycerides. Too much niacin can also raise blood sugar and damage the liver. If you take niacin, mention it when you discuss blood lipid, glucose or liver values with your doctor.
What is pellagra? +
Pellagra is the result of severe niacin deficiency. Typical signs are digestive problems, inflamed skin and impaired mental function. Where many foods are fortified with B vitamins, vitamin B deficiency is less common.
Do I need to fast for the test? +
Before a blood sample for a vitamin B test you may need to avoid eating or drinking for several hours. A urine test needs no special preparation. Your practice or the lab will tell you what applies to your test.
Vitamin B3 (niacin)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.