Chemistry:Niacin (nutrient)
Vitamin B3 is a vitamin family that includes three forms or vitamers: nicotinamide (niacinamide), niacin (nicotinic acid), and nicotinamide riboside.[1] All three forms of vitamin B3 are converted within the body to nicotinamide adenine dinucleotide (NAD).[1] NAD is required for human life and people are unable to make it within their bodies without either vitamin B3 or tryptophan.[1] Nicotinamide riboside was identified as a form of vitamin B3 in 2004.[2][1]
In the past, the group was loosely referred to as vitamin B3 complex.[3]
Mechanism of action
NAD, along with its phosphorylated variant nicotinamide adenine dinucleotide phosphate (NADP), are utilized in transfer reactions within DNA repair and calcium mobilization. NAD also plays a critical role in human metabolism, acting as a coenzyme in both glycolysis and the Krebs cycle. [4]
Sources
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. population on average has an intake of niacin that is well above the recommended dietary allowance (RDA).[4]
Toxicity
The daily limit for vitamin B3 has been set at 35 mg. At daily doses of as low as 30 mg, flushing has been reported, always starting in the face and sometimes accompanied by skin dryness, itching, paresthesia, and headache.[4] Liver toxicity is the most serious toxic reaction and it occurs at doses >2 grams/day.[5] Fulminant hepatitis has been reported at doses between 3-9 grams/day with needs for liver transplantation. Other reactions include glucose intolerance, hyperuricemia, macular edema, and macular cysts.[4]
Deficiency
Vitamin B3 deficiency can cause pellagra, a disease found in many alcoholics in North America. Symptoms include vomiting, loss of appetite, abdominal pain, and general fatigue.[4] Drinking too much alcohol can lead to vitamin B3 deficiency. Chronic alcoholism can cause vitamin B3 deficiency because it affects both the intake and absorption of vitamin B3. Drinking excessive amounts of alcohol blunts the appetite, so people who are chronic alcoholics may not be eating enough food to sustain a healthy level of vitamin B3. Over time, chronic alcohol intake also affects the body's ability to absorb and use niacin. Some doctors routinely prescribe niacin to people with alcohol use disorders.
References
- ↑ 1.0 1.1 1.2 1.3 Stipanuk, Martha H.; Caudill, Marie A. (2013) (in en). Biochemical, Physiological, and Molecular Aspects of Human Nutrition - E-Book. Elsevier Health Sciences. p. 541. ISBN 9780323266956. https://books.google.com/books?id=XVNPAQAAQBAJ&pg=PA541. "Vitamin B3... potentially includes three different molecular forms: nicotinic acid, niacinamide, and nicotinamide riboside"
- ↑ Bieganowski, P; Brenner, C (14 May 2004). "Discoveries of nicotinamide riboside as a nutrient and conserved NRK genes establish a Preiss-Handler independent route to NAD+ in fungi and humans.". Cell 117 (4): 495–502. doi:10.1016/s0092-8674(04)00416-7. PMID 15137942.
- ↑ Silvestre, Ricardo; Torrado, Egídio (2018) (in en). Metabolic Interaction in Infection. Springer. p. 364. ISBN 978-3-3197-4932-7. https://books.google.com/books?id=Y6VUDwAAQBAJ&pg=PA364. "Niacin or nicotinate, together with its amide form nicotinamide, defines the group of vitamin B3 complex"
- ↑ 4.0 4.1 4.2 4.3 4.4 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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