Vitamin B3 (Niacin)

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Vitamin B3

Good sources: meats, liver, nuts, whole and enriched grains. Some niacin can be synthesized from tryptophan (inefficient).

DRI: 12-16 mg/d

Functions: Co-enzyme formation (NADand NADP), fatty acid metabolism, and decrease serum cholesterol. It is the most potent agent to increase serum HDL at doses 100 times the RDA (but many people can’t tolerate the side effects). It does this by strongly inhibiting lipolysis in adipose tissue, which is the largest producer of circulating FFA’s. Decreased FFA’s are needed for the formation of VLDLs. LDLs are produced from VLDLs. Thus, niacin inhibits the formation of  LDLs (indirectly). It is especially useful for the treatment of type IIb hyperlipidemia (both VLDL and LDL levels are increased).

    • Also called nicotinic acid or niacinamide or nicotinamide (not related to nicotine found in tobacco)
    • Nicotinic acid & niacinamide have identical vitamin properties but are different pharmacologically
    • Around 200 enzymes require niacin derived NAD or NADP enzymes (also called coenzyme I and
  • coenzyme II) usually for redox reactions

    • Coenzyme for NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine
  • dinucleotide phosphate) which is needed to metabolize food

    • Increases the rate of NAD synthesis
    • NADP regenerates glutathione
    • Cofactor in the mitochondrial respiratory chain
    • NAD catabolizes carbohydrates, proteins, fats and alcohol
    • Cofactor to mitochondrial aldehyde dehydrogenase which metabolizes alcohol
    • Cofactor to glucose-6-phosphate 1-dehydrogenase which metabolizes glucose in red blood cells
    • Cofactor to dihydropteradine reductase which is involved in dopamine and serotonin synthesis
    • NADP synthesizes fatty acids and cholesterol
    • Only nicotinic acid influences blood lipid levels
    • Increases HDL (high density lipoprotein)
    • Lowers triglycerides by inhibiting diacylglycerol acyltransferase-2 (enzyme that synthesizes
  • triglycerides in liver)

    • Cofactor to long-chain-3-hydroxyacyl-CoA dehydrogenase which metabolizes fat for energy
    • Down regulates vascular cell adhesion molecules (VCAM)
    • Inhibits the oxidation of LDL (low density lipoproteins)
    • Decreases the highly atherogenic Lp(a) by reducing its rate of synthesis in the liver
    • Shifts lipoproteins from small, dense (atherogenic) to large, buoyant (non atherogenic)
    • Inhibits vascular inflammation and improves endothelial function independent of effect on lipids
    • Supresses cytokine-mediated induction of nitric oxide synthase, thus decreasing inflammation
    • Cofactor in mono-ADP-ribosyltransferase, which plays a role in cell signaling
    • Cofactor in poly-ADP-ribose polymerase (PARP), which aid in DNA replication and repair
    • Cofactor in ADP-ribosyl cyclase, which initiates release of calcium ions from inside cell
    • Maintains proper methylation of PARPgenes that suppress tumor formation and growth
    • Influences cellular response to DNA damage (cancer prevention)
    • Extends lifespan of human cells in vitro
    • Slows telomere attrition rate by reducing reactive oxygen species in mitochondria
    • Mediates cell signaling pathways important to the prevention of cancer
    • Regulates p53 activity in cells (a protein that protects against tumors)
    • Protect pancreatic beta cells in type 1 diabetics although high doses may impair glucose tolerance
    • Precursor to glucose tolerance factor which facilitates insulin binding
    • Pharmacological doses may enhance calming effect of GABA (gamma aminobutyric acid) in brain
    • Pharmacological doses may exacerbate gout or cause hepatotoxicity (liver damage)
    • Inhibits the enzyme tryptophan pyrrolase which breaks down tryptophan in the liver
    • Increases conversion of tryptophan to serotonin
    • Increases REM (rapid eye movement) sleep
    • Improves quality and quantity of sleep via its role in serotonin synthesis
    • Dilates blood vessels (may alleviate migraine)
    • Severe deficiency can cause anxiety
    • Increases adiponectin (weight loss hormone secreted by fat cells)
    • Niacin-bound chromium may help reduce body weight

Deficiencies:  Clinical signs of early niacinamide deficiency include anorexia, muscular fatigue, indigestion, depression, insomnia, headaches, glossitis and skin lesions. Severe deficiency may lead to pellagra, with dermatitis, dementia, diarrhea (the 3 D’s of pellagra), tremors and sore (black) tongue. Deficiencies of thiamin, riboflavin and pyridoxine commonly accompany (or can cause) niacinamide deficiency.

Toxicity: Histamine reaction at doses >35 mg. Facial flushing is one of the symptoms of this.