Vitamin B3 (Niacin, Niacinamide)

Chart 1. Differences Between Niacin and Niacinamide
	Niacin	Niacinamide
Naturally occurs in foods	Yes	Yes
To fortify foods	No	Yes
In supplements	Yes	Yes
Treats vitamin B3 deficiency	Yes	Yes
Raises HDL, lowers LDL	Yes	No
Causes flushing	Usually	Rarely

Recommended Daily Intake

The Recommended Dietary Allowance (RDA) for vitamin B3 for adult men is 16 mg/day, for women 14, during pregnancy 18 and during breastfeeding 17 mg/day ^[1].

Vitamin B3 Supplements

Forms without prescription (over-the-counter):

• Niacin and niacinamide:
  • Crystalline or immediate-release
  • Slow- or sustained-release
  • As part of vitamin B complex vitamins and multivitamins
• Inositol hexanicotinate (“flush-free” niacin)

Prescription forms:

• Niacin:
  • Intermediate release
  • Extended-release

Possible Benefits

Vitamin B3 supplements are effective for ^[1,9]:

• Prevention and treatment of niacin deficiency
• Increasing HDL and decreasing LDL cholesterol and decreasing triglyceride levels. This effect can be achieved by niacin (but not nicotinamide or inositol hexanicotinate) in high amount (2-3 g/day). Antioxidants (beta carotene, vitamin C and E, selenium) decrease the niacin’s HDL raising effect ^[9,18].

Vitamin B3 is possibly effective for ^[1,9]:

• Cardiovascular disease. According to one 2010 meta-analysis ^[10] and one 2012 systematic review ^[11], niacin (but not nicotinamide) reduces “cardiovascular events” but not necessary by increasing HDL cholesterol and not necessary in all individuals.
• Lowering phosphate levels in individuals with kidney disease on hemodialysis (both niacin and nicotinamide) ^[12].

There is insufficient evidence about vitamin B3 supplements effectiveness in prevention or treatment of acne, age-related macular degeneration (AMD), alcohol dependence, Alzheimer’s disease, anemia, anxiety, arthritis, attention deficit-hyperactivity disorder (ADHD), Bell’s palsy, blood flow disorders, cancer, cataracts, depression, diabetes mellitus type 1 or 2, diarrhea, dizziness, erectile dysfunction, glossitis (tongue inflammation), drug-induced hallucinations, hepatic encephalopathy, hepatitis C, hearing loss, high blood pressure, HIV/AIDS, insomnia, liver disease, menstrual pain, migraine headache, motion sickness, multiple sclerosis, osteoarthritis, parasite infestation, Raynaud’s disease, ringing in the ears (tinnitus), seizures (epilepsy), skin conditions, stroke, swelling (edema), tardive dyskinesia (involuntary movements), thrombosis, thyroid disorders, tuberculosis, ulcers, vasculitis, vascular spasm, vertigo, wound healing ^[13,17].

It is also insufficient evidence about the vitamin B3 effectiveness as an antioxidant, anti-agent substance, growth, memory, sexual arousal or weight loss enhancer, sedative, aid in smoking cessation or sun protection ^[17].

Vitamin B3 Safety: Side Effects, Toxicity

The Tolerable Upper Intake Level (UL)–the amount that should not cause side effects–for non-prescribed (OTC) niacin and niacinamide for adults is 35 mg/day ^[1].

Possible side effects of niacin, but less likely niacinamide, supplements in usual doses: flushing, paresthesia (tingling), rashes, jaundice, itch, skin hyperpigmentation, nausea, mouth pain, runny nose, slightly elevated blood glucose, stomach upset, intestinal gas, low blood pressure, dizziness, excessive sweating, irregular heartbeat (arrhythmia), worsening of gallbladder disease and allergies ^[1,9,14,19].

Niacin Flush Reaction

Niacin, but less likely niacinamide, supplements in high doses (>50 mg) can cause flushing of the face, arms and chest; flushes usually appear within 15-30 minutes (or up to 4 hours) after taking and may last for 1-2 hours ^[6,20]. Flushing increases with the dose and can be prevented by slowly increasing the dose to the prescribed dose over several weeks and by taking it with food. Aspirin in a low dose (325 mg), 30 minutes before niacin, can prevent flushing ^[20]. Tolerance to flushing often develops in several weeks ^[14]. Flushing is due to skin vessels dilation ^[19].

Over-the-counter immediate-release niacin tablets cause flushing more likely than slow-release ones; the prescription extended-release niacin causes flushes the least likely ^[16].

Foods and drugs that can worsen flushing when taken along with niacin: alcohol, hot drinks, zinc supplements and nicotine patches ^[9].

“No-flush” niacin usually contains inositol hexanicotinate, which releases niacin slowly and does not cause flushes but also provides your body with only little niacin and is not effective in raising HDL cholesterol levels ^[16].

Niacin and Drug Tests

There is no scientific evidence that niacin can alter the results of drug tests ^[15].

Overdose

Niacin or niacinamide doses higher than 3 g/day may cause dry skin, fever, diarrhea, vomiting, frequent urination, joint pain, muscle aches, unusual thirst or tiredness, liver, gallbladder, stomach, intestinal or kidney problems, gout, blurred vision, high blood sugar, irregular heartbeat, low platelet count (thrombocytopenia) ^[9,19].

Who should avoid niacin?

Do not take vitamin B3 supplements if you have liver or kidney damage, peptic ulcer, bleeding problems or allergy to niacin and stop taking them at least two weeks before scheduled surgery ^[14].

During Pregnancy and Breastfeeding

Niacin is a pregnancy category C drug, which means no harmful effects have been observed in human infants so far but insufficient studies have been done to exclude all possible adverse effects ^[14]. Speak with your doctor if you intend use niacin during pregnancy or breastfeeding.

Vitamin B3 Interactions With Drugs

• A combination of niacin and statins (lovastatin, simvastatin) may, rarely, cause a breakdown of muscle fibers (rhabdomyolysis) resulting in a kidney failure.
• A combination of niacin and clonidine may cause low blood pressure (hypotension).
• A combination of niacin and chromium may cause low blood sugar (hypoglycemia).
• Niacin in combination with androstenedione, borage leaf, chaparral, comfrey, dehydroepiandrosterone (DHEA), germander, kava, pennyroyal oil or red yeast extract may cause liver damage.
• Cholestyramine and colestipol may reduce the absorption of niacin and niacinamide.
• Niacin may reduce the effectiveness of allopurinol, sulfinpyrazone and probenecid in treating gout.