Over-the-counter niacin supplements above 35 mg a day can cause flushing, so 100 mg may cause that. Ask your doctor before taking it.
Limits
The tolerable upper intake level (UL) for niacin from supplements is 35 mg a day for adults.
100 mg
This exceeds the UL, so flushing is common: redness, warmth and itching in the face and neck within 15 to 30 minutes.
RDA
14 mg for women and 16 mg for men.
Side effects of high doses
Flushing, nausea, liver damage, high blood sugar.
Safer forms
Niacinamide doesn’t flush.
Talk to a doctor
Before taking more than the UL, such as for cholesterol.
Dose context
The recommended dietary allowance for niacin (vitamin B3) is 16 mg niacin equivalents (NE) for adult men and 14 mg NE for adult women. The tolerable upper intake level from supplements and fortified foods is 35 mg per day. So 100 mg is above the upper limit.
- Nicotinic acid in doses of 30 to 50 mg or more can cause flushing: red, warm skin with itching and tingling.
- Therapeutic doses of 1,000 to 3,000 mg are used for cholesterol under medical supervision, and can damage the liver.
- Niacinamide (nicotinamide) does not cause flushing but has the same upper limit of 35 mg.
Safety
In large trials such as AIM-HIGH (2011) and HPS2-THRIVE (2014), adding niacin to statins did not reduce cardiovascular events and caused more side effects. People with liver disease, gout, ulcers or diabetes should not take high-dose niacin without medical advice. Food sources include chicken, tuna, peanuts and fortified cereals. Ask a doctor or pharmacist before taking 100 mg supplements.
Dose context
The recommended dietary allowance for niacin is 16 mg for men and 14 mg for women. The tolerable upper intake level is 35 mg a day from supplements and fortified foods, and 100 mg is far above it. Doses of 50 to 100 mg can cause flushing, itching and tingling. Prescription doses for cholesterol are 500 to 2,000 mg under medical supervision.
Safety
High dose niacin can raise liver enzymes, blood sugar and uric acid. Talk to a doctor before taking it, especially with liver disease, diabetes or gout. Large trials such as AIM-HIGH did not show added heart benefit when added to statins.
Forms and risks of niacin
Niacin comes as nicotinic acid (causing flushing), nicotinamide and inositol hexanicotinate. Doses of 50 mg or more of nicotinic acid commonly cause flushing, itching and low blood pressure. The upper limit is 35 mg a day. Prescription extended release niacin of 1,000 to 2,000 mg a day lowers triglycerides and raises HDL, but large trials (AIM-HIGH, HPS2-THRIVE) found no reduction in heart events with statins and more side effects.
Safe approach
Getting niacin from food such as chicken, tuna, peanuts and fortified cereal meets needs. Do not use high dose supplements without a clinician. Warning signs include dark urine, yellowing skin or severe stomach pain, suggesting liver injury. Niacin can raise blood sugar and uric acid. Pregnant women and people with liver disease or ulcers should avoid high doses.
Based on data from the NIH Office of Dietary Supplements and the New England Journal of Medicine
