Vitamin B3, or Niacin/Nicotinic Acid/Nicotinate to which it is also referred, is a water-soluble micronutrient. It can also be found in a form called Niacinamide/Nicotinamide. Both forms of vitamin B3 have different applications. Vitamin B3 is important in over 50 chemical reactions in the body especially those related to energy production; fat, cholesterol, and carbohydrate metabolism; and the synthesis of many body compounds including sex and adrenal hormones. It can be obtained through dietary sources but is also synthesized in the body via the conversion of tryptophan to niacin.
The following foods have the highest concentration of vitamin B3. For a more expansive list on food sources of specific nutrients visit Health Canada's Dietary Reference Intakes for Vitamins or USDA's National Nutrient Database
Other food sources include:
- grains: whole grains (except corn)
- protein sources: liver and other organ meat, fish,
- fruit: avocados
- dairy: milk, eggs
- Other sources include: peanuts, legumes
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The following are the primary uses of Vitamin B3.  
- Pellagra: the most well-known vitamin B3 deficiency. It is more accurate to call it a tryptophan deficiency as tryptophan can cure it in its early stages. It closely resembles schizophrenia in its earlier stages and is considered a schizophrenic syndrome.
- Hypercholesterolemia: This is one of the major uses for therapeutic supplementation of vitamin B3. It acts to lower high cholesterol levels while elevating high density lipoprotein (HDL) cholesterol levels ("good" cholesterol). The form used to lower blood cholesterol is the niacin form.
- Recent-onset Type I Diabetes: An early pilot study testing the effects of vitamin B3 on individuals with recently diagnosed type I diabetes suggests that it slows the progression of the disease in some individuals if administered as close as possible to the onset. Since this pilot study, more studies have been done which confirm these findings. The positive results were "prolonged noninsulin-requiring remission, lower insulin requirements, improved metabolic control, and increased beta-cell function."  It also enhances insulin secretion and increases sensitivity.  The form used to treat early onset type I diabetes is niacinamide (nicotinamide).
- Erectile Dysfunction: Niacin alone can improve the erectile function in patients suffering from moderate to severe ED and dyslipidemia.
- Arthritis: Clinical experience has shown that niacinamide (nicotinamide) at high doses has also shown positive results in terms of the treatment of osteoarthritis and rheumatoid arthritis.
- Schizophrenia: the other major use for therapeutic supplementation of vitamin B3.
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- Hypochlorhydria (low stomach acid): the vitamin plays an integral role in the proper functioning of the stomach and a healthy digestive system by facilitating proper stomach acid secretion.
- Migraine and Tension-type Headaches: IV and oral doses cause cutaneous flushing that might mitigate or abort the acute symptoms of migraine by vasodilating the intracranial vessels, thus preventing the subsequent vasoconstriction of the extracranial vessels.
- Anxiety Disorders: Niacinamide]] is the most effective form over niacin as it has a better ability to affect the central nervous system as it crosses the blood-brain-barrier. It appears to have an anxiolytic effect through the modulation of neurotransmitters which are commonly unbalanced in anxiety.
- HIV Infections: HIV-infected individuals share some common symptoms with pellagra patients: tryptophan depletion, intracellular NAD (an active form of niacin in the body) depletion, and idopathic dermatitis, diarrhea, and dementia. Niacinamide also exerts an antimicrobial action against HIV.
- Detoxification: Niacin encourages detox in the body.
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- Others: learning and behavioural disorders in children, alcoholism, drug addiction, some senile states, absorption problems, Huntington's Disease, antidote against LSD intoxication, decreases risk of leukemia after the original cancer is cured, improves healing, inhibits development of Alzheimer's disease (decreases onset of dementia, increases longevity) prevents juvenile diabetes, treats arthritis, prevents cardiovascular disease, treats kidney disease
- Pellagra - described by the 4 Ds
- Dermatitis - cracked, thick, scaly skin forming symmetrical, darkly pigmented rash made worse in the sun
- Diarrhea - results from decreased hydrochloric acid in the stomach leading to GI inflammation
- Dementia (late stage) - irritability, headaches, insomnia, followed by mental confusion, amnesia, hallucinations and severe depression
- Death - when left untreated
- Acute Deficiency - scarlet glossitis (inflamed, burning, bright, beefy red appearance of the tongue) and stomatitis
As Niacin is a water soluble vitamin, excess consumption or supplementation is typically excreted in the urine. Doses that are too high for an individual may result in: loss of appetite (initially), followed by nausea and eventually vomiting.
Common Deficiency Tests: 
- Lactate and pyruvate urine test - positive result is high
- Vitamin B3 is available in supplements as either niacin (nicotinic acid or nicotinate) or niacinamide (nicotinamide). Each form serves a different purpose.
- The niacin form is useful for lowering blood cholesterol.
- The niacinamide form is useful for arthritis and early-onset type I diabetes.
- The niacin form in doses of greater than 50mg causes a transient flushing of the skin. There are also time-released formulations that are intended to decrease this side effect. However, these preparations are more toxic to the liver. A better way to avoid flushing is to use inositol hexaniacinate (also known as inositol hexanicotinate and hexaniacin) 
- The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- Infants: 5mg (under 6 months); 6mg (6-12 months)
- Child: 9mg (1-3 years); 12mg (4-6 years); 13mg (7-10 years)
- Adolescent: 17mg (Males 11-14 years); 20mg (Males 15-18 years)
- Adult: 19mg (Males 19-50 years); 15mg (Females 11-50 years); 15mg (Males 51+ years); 13mg (Females 51+ years)
- Pregnancy: 17mg
- Lactation: 20mg
- Children (under 12): use of Niacin supplementation during this time is not recommended because of insufficient research on safety and effectiveness and diminished hepatic detoxification capacity.
- Pregnancy and Breastfeeding: use of Niacin supplementation during this time is not recommended because research on safety and effectiveness is insufficient.
- Contraindications: in those with hypersensitivity to Niacin
- Side effects: The most common and well-known side effect of Niacin is flushing. The flush usually begins in the forehead with a tingle and then intensifies. It travels down to the face and usually stops at the chest but may move downwards. With continued use, the flush typically recedes. Nicotinamide is not associated with flushing. Time released formulas have been made to decrease this side effect but they are more toxic to the liver.
- Specific populations with increased susceptibility to adverse effects: include alcohol abuse, cardiac arrhythmias, severe hypotension, inflammatory bowel disease, and migraine headaches.
- Compromised Liver Function - avoid or closely supervise
- Type II Diabetes and Hypoglycemia - Nicotinic Acid can induce elevation in blood glucose and depletion of glycogen stores. Clinical management is necessary.
- Gout - Niacin can increase uric acid production and elevate blood uric acid concentrations. Close supervision is necessary.
- Hyperhomocysteinemia, elevated risk of stroke or Heart Disease - Niacin may elevate plasma homocysteine levels. Close supervision is necessary.
- Peptic Ulcers - Niacin aggravates ulcers. Avoid except under close supervision.
- Bleeding Disorders, Anticoagulant Therapy - Niacin rarely causes leukopenia and slightly increase blood eosinophils.
Drug interactions include:
- Supportive or Beneficial:
- Acetylsalicylic Acid (ASA, aspirin, Acetaminophen, Nonsteroidal Anti-inflammatory Drugs (NSAIDs) - Co-administration may moderate superficial adverse effects associated with Niacin (i.e., flushing and itchiness).
- Anticonvulsant Medications, Including Phenobarbital, Phenytoin, and Valproic Acid - Niacin can potentiate the action of these drugs enhancing drug activity and possibly allowing lowering of dosage.
- Bile Acid Sequestrants - Co-administration provides an additive effect on lipid lowering. Intake should be separated by 4-6 hours as bile acid sequestrants and Niacin may actually interfere with the absorption of each other if ingested at the same time.
- Gemfibrozil and Related Fibrates - Co-administration can provide complementary cardioprotective effects and reduce risk of vascular events (Niacin works to increase HDL and fibrates work to decrease triglycerides. Both can, however, cause hyperhomocysteinemia (except Gemfibrozil) therefore monitor homocysteine levels.
- Thioridazine - Concomitant administration may cause increased therapeutic effect.
- Addresses Drug-Induced Deficiency:
- Isoniazid, Rifampin, and Related Antitubercular Agents - Co-administer Niacin and B6 especially with nutritionally compromised patients and always with long-term use of these drugs.
- Mercaptopurine, Azathioprine, and Thioguanine (Thiopurines) - Co-administer Niacin especially with nutritionally compromised patients and always with long-term use of these drugs.
- Tetracyline Antibiotics - Separate intake if concurrent administration (by at least 4 hours) due to Niacin impairing absorption and bioavailability of the drug.
- Tricyclic Antidepressants (TCAs) - Niacinamide administration reduces peripheral breakdown of tryptophan to niacin thus allowing tryptophan to exert its serotonin-like effect and allowing potentiation of TCAs.
- Ursodeoxycholic Acid and Chenodeoxycholic Acid - Concomitant use of these drugs with Niacin may reduce the antihyperlipidemic activity of the vitamin.
- Insulin, Biguanides, Meglitinide Analog Oral Hypoglycemics - Niacinamide may be supportive as it supports pancreatic beta cells, enhances insulin secretion, and increases insulin sensitivity potentially delaying onset or reducing symptoms of type 1 diabetes mellitus. May warrant reduced insulin dose. Niacin influences glucose tolerance but may elevate glucose levels and therefore may antagonize to hypoglycemic drugs. However, Niacin can also be synergistic especially in patients with co-morbid dyslipidemia and type 2 diabetes and metabolic syndrome.
- HMG-CoA Reductase Inhibitors (Statins) - Co-administration exerts an additive effect on lipid lowering (Niacin acts to increase HDL, and statins act to decrease LDL). Combined effect also increases risk of hepatotoxicity, myositis, and other adverse effects. Co-administration may still be appropriate in some cases but requires professional management and is contraindicated in others.
Nutrient interactions include:
- Antioxidant - Co-administration of antioxidants and Niacin may blunt the therapeutic effect of niacin on lipid lowering.
- Betaine - Co-administration may alleviate the hepatotoxic risk associated with niacin therapy.
- Chromium - Concomitant intake may improve glucose tolerance, particularly in individuals whose diet provides inadequate levels of dietary nicotinic acid and chromium. A hypoglycemic event is possible therefore professional management is indicated.
- S-Adenosylmethionine (SAMe) - Co-administration may decrease adverse effects associated with niacin.
- Vitamin B6 - Co-administration could reasonably be expected to mitigate the effects of hyperhomocysteinemia and hypocysteinemia seen with niacin therapy.
- ↑ Medlineplus 
- ↑ 2.0 2.1 2.2 2.3 Murray Michael T (2005) Encyclopedia of Nutritional Supplements, The Essential Guide for Improving Your Health Naturally, Prima Publishing
- ↑ Hoffer Abram, Prousky Jonathan (2006) Naturopathic Nutrition, a Guide to Health Food and Nutritional Supplements, CCNM Press
- ↑ Ng CF, Lee CP, Ho AL, Lee VW (Oct 2011) Effect of niacin on erectile function in men suffering erectile dysfunction and dyslipidemia. J Sex Med.;8(10):2883-93. PMID: 21810191.
- ↑ Bralley J Alexander and Lord Richard S (2005) Laboratory Evaluations in Molecular Medicine, Nutrients, Toxicants, and Cell Regulators Institute for Advances in Molecular Medince, GA
- ↑ 6.0 6.1 Stargrove Mitchell Bebell, Treasure Jonathan, McKee Dwight L (2008) Herb, Nutrient, and Drug Interactions, Clinical Implications and Therapeutic Strategies. Mosby