Niacin Side Effects on the Liver


Niacin, also known as vitamin B3 or nicotinic acid, is a water-soluble vitamin that is used as a cholesterol and blood lipid (fat) lowering agent. The side effects of niacin include flushing and gastrointestinal disturbances, and at higher-sustained doses hepatotoxicity (liver damage). The immediate-release form of niacin is associated with less toxicity to the liver than other forms.


Niacin is used in the body to produce nicotinamide, which is the building block of coenzymes nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP). NAD functions primarily in capturing active phosphates (energy) during the breakdown (catabolic) of carbohydrates, fats, proteins and alcohol. NADP functions primarily in donating active phosphates during the production (anabolic) of carbohydrates, proteins, fats and cholesterol.


The recommended daily allowance (RDA) for niacin is 14 and 16 mg/day for women and men, respectively. Niacin will treat and prevent niacin deficiency (Pellagra) and lower cholesterol and lipids in the blood. Pellagra is common in people who rely heavily or exclusively on unprocessed maize (corn) as a dietary staple. However, traditional methods of preparing corn dough (masa) allows niacin to become bioavalible, thus preventing pellagra. Niacin blocks the release of lipids into the blood and is useful for treating a wide variety of blood lipid disorders. It lowers low-density-lipoprotein (LDL) cholesterol, triglycerides and lipoprotein A. It also increases "good" high-density-lipoprotein (HDL) cholesterol.

Side Effects on Liver

The most reported side effect of increase niacin intake is flushing (warm, itching, red, or tingly skin). These symptoms appear at the upper intake (UI) level of 30 to 35 mg/day but can be minimized by slowly building up to higher doses of niacin, and typically improve over time. Hepatotoxicity is reported after months of daily doses of 500 to 750 mg/day. Side effects on the liver include elevated liver enzymes, jaundice and hepatitis. Due to these potential side effects, medical supervision is recommended when nicotinic acid is used above the UI level.

Types of Niacin

Niacin supplements are available as nicotinamide or nicotinic acid. Nicotinamide is typically found in fortified foods, and nicotinic acid is available over the counter or by prescription. Nicotinic acid is available in immediate-release, extended- release and slow-release forms. Immediate-release nicotinic acid is associated with less liver toxicity than extended- release and slow-release forms.

Expert Insight

Niacin is safe to consume at or below the UI (30 to 35 mg/day). Hepatic toxicity is common with higher doses of slow-release niacin, less common with extended-release niacin, and rare with immediate-release forms. If high doses and continuous use are being taken or considered, seek advice and monitoring by a medical professional of blood lipid profiles and liver function.

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