Vitamin B3 is a vitamin that includes three forms: nicotinamide (niacinamide), niacin (nicotinic acid), and nicotinamide riboside. All three forms of vitamin B3 are converted within the body to nicotinamide adenine dinucleotide (NAD). NAD is required for human life and people are unable to make it within their bodies without one of the vitamin B3 or tryptophan. Nicotinamide riboside was identified as a form of vitamin B3 in 2004. The group is also occasionally referred to as vitamin B3 complex.
Mechanism of action
Vitamin B3 is highly absorbed from food sources such as: beans, milk, meat, and eggs. It is also highly bioavailable from enriched flour, which has the non-coenzyme form referred to as "free" niacin. Cereal grains are not high sources of niacin. The U.S. on average has an intake of niacin that is well above the recommended dietary allowance (RDA).
The daily limit for vitamin B3 has been set at 35 mg. At daily doses of as low as 30 mg, flushing has been observed, always starting in the face and sometimes accompanied by skin dryness, itching, paresthesia, and headache. Liver toxicity is the most serious toxic reaction and it occurs at doses >2 grams/day. Fulminant hepatitis has been reported at doses between 3-9 grams/day with needs for liver transplantation. Other reactions include:
- Stipanuk, Martha H.; Caudill, Marie A. (2013). Biochemical, Physiological, and Molecular Aspects of Human Nutrition - E-Book. Elsevier Health Sciences. p. 541. ISBN 9780323266956.
Vitamin B3... potentially includes three different molecular forms: nicotinic acid, niacinamide, and nicotinamide riboside
- Silvestre, Ricardo; Torrado, Egídio (2018). Metabolic Interaction in Infection. Springer. p. 364. ISBN 978-3-3197-4932-7.
Niacin or nicotinate, together with its amide form nicotinamide, defines the group of vitamin B3 complex
- Suter, Paolo; Russell, Robert (2018). "Chapter 326: Vitamin and Trace Mineral Deficiency and Excess". Harrison's Principles of Internal Medicine, 20th Ed. New York, NY: McGraw-Hill. ISBN 978-1259644030.
- Goodman & Gilman's the pharmacological basis of therapeutics. Goodman, Louis S. (Louis Sanford), 1906-2000., Hardman, Joel G., Limbird, Lee E., Gilman, Alfred Goodman, 1941-2015. (10th ed.). New York: McGraw-Hill. 2001. ISBN 0071354697. OCLC 46548349.
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