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Vitamin B3 (Niacin)

What is vitamin B3?

Niacin is another B-vitamin that is commonly known by its name rather than its number, B3. It also goes by many names and many forms depending on its source.

It is also known that the bacteria of the large intestine produce nicotinic acid, although it is unclear what contribution this makes to overall niacin levels. Niacin is thought to have anti-inflammatory roles in the colon and digestive tract and has been associated with reducing inflammation of the colon.

What does the body use Niacin for?

Niacin is involved in over 200 reactions in the human body. Similarly to other B-vitamins, B3 plays roles in the processes of nutrient metabolism and energy production. It also aids in cellular processes such as DNA repair and activity. Needless to say, Niacin is pretty important!

Dietary Reference Intakes (DRIs)

The amount of niacin you need depends on your sex and age. Recommendations for niacin are also expressed in niacin equivalents (NE). The requirements listed in the chart are expressed in NE, with the exception of recommendations for infants younger than six months, which are expressed in terms of pre-formed niacin. Infant requirements for all nutrients are expressed in terms of Adequate Intake, or AI.

Helpful terms to know

  • Recommended Dietary Allowance (RDA): covers the needs of 97-98% of individuals in a group; the average amount of a nutrient a healthy person should consume daily. Vary by gender, age, and whether a woman is pregnant or breastfeeding. Developed by the Food and Nutrition Board at the Institutes of Medicine (IOM) of the National Academies.

  • mg = milligram

  • Adequate Intake (AI): recommended daily intake of a nutrient; established by Institute of Medicine (IOM) to meet or to exceed the needed amount to maintain adequate nutrition for most people in a particular stage of life or gender group; established when not enough evidence is available to determine the RDA


An interesting thing about niacin deficiency is that it affects humans and canines in different ways. In humans, the deficiency is called Pellagra and in canines (dogs) it is known as “black tongue”. In times of vitamin imbalance, both humans and dogs experience significant effects to their mouth, lips, or tongue.

Who is at risk for a niacin deficiency?

Individuals that may be prone to a deficiency of B3 generally fall in the following categories:

  • Hartnup disease (defective tryptophan transporter, which impairs niacin conversion from tryptophan)

  • Inadequate intake of riboflavin (B2), vitamin B6, or iron

  • Nutrient-medication interactions

  • Malabsorptive conditions

    • chronic diarrhea

    • Inflammatory Bowel Disease (IBD)

    • intestinal cancer

  • High alcohol intake

  • Increased vitamin B3 needs

    • HIV

    • cancer or undergoing chemotherapy


Niacin supplementation, even in accepted amounts, can have unwanted side effects. This means that you should definitely be aware of vitamin B3 and its upper limit. The upper limit for adults has been set at 35 mg/day. Again, I want to emphasize that there can be side effects even before reaching this amount from niacin supplementation, so keep that in mind if you are considering a supplement.

How to determine levels of niacin

These tests should be run under direct medical supervision. Ask your doctor and dietitian for more information. Your niacin status can be assessed through measurement of the following:

  • Urinary metabolites: measures levels of the different forms of niacin that are excreted in the urine

    • Methyl nicotinamide (~0.8 mg/day N’ methyl nicotinamide and ~0.5 mg N’ methyl nicotinamide/1 g creatinine suggest deficiency)

  • Serum or Red Blood Cell Indicators

    • NAD concentrations

    • Ratio of NAD to NADP

Sources of Niacin

Niacin is found in many food groups. Some sources, however, like corn contain a form of niacin that is relatively unavailable. Research has shown that in some cases, treatment of these foods with lime water might be able to increase the availability of vitamin B3 in these foods.

How stable is Niacin?

Niacin experiences minimal losses when exposed to cooking or storage.

Supplementation & Treatment with Niacin


Niacin is used to treat hyperlipidemias (high blood lipids), lower serum cholesterol and low-density lipoproteins (LDL) and to increase high-density lipoproteins (HDL, more commonly known as the “good” cholesterol).

In some cases, a topical form of niacin is used for acne vulgaris or non-melanoma skin cancers. To treat deficiency, oral nicotinamide is typically administered at 300 mg/day (usually in three separate doses of 100 mg spread throughout the day to avoid upset or negative side effects) for the duration of about one month.

Significant Side Effects

As mentioned above, niacin supplementation (even at low levels of 30-50 mg/day) can cause many side effects. The risks of supplementing should be weighed against the potential benefits.

Dietary Supplements

Those being treated for conditions necessitating large doses of this vitamin should do so 1) under medical supervision, and 2) only after considering the potential toxic side effects weighed against the potential benefits for that individual.


Extended release forms of niacin supplements may help to reduce side effects. Your healthcare team can also design a vitamin regimen that appropriately spaces out your dosage to reduce side effects. Ask your doctor or dietitian for more information about adjusting your dosage and delivery method.


FREE Patient Resources

Vitamin B3 (Niacin)_ Reference_pdf_pt_fr
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Related Professional Resources

Don't you wish you had a quick reference to brush up on niacin before seeing your clients or patients? This quick reference will help you organize your thoughts and prove to be a great resource in between appointments.


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  1. Pronsky ZM, Elbe D, Ayoob K. Food Medication Interactions (The Foremost Drug-Nutrient Interaction Resource), Micronutrient Food Sources. 18th Edition. 2015. ISBN: 978-0-9710896-6-2

  2. Hart J. Eat Pretty. Chronicle Books. 2014. ISBN 978-1452123660.

  3. Gropper SS, Smith JL, Carr TP. Advanced Nutrition and Human Metabolism, Seventh Edition. Cengage Learning. 2017. ISBN: 978-1305627857.


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