Niacin is a water-soluble vitamin belonging to the B-complex family. The term "niacin" actually applies to two different compounds -- niacinamide and nicotinic acid -- both of which are converted in your body to a physiologically active molecule called nicotinamide adenine dinucleotide, or NAD. NAD and its phosphorylated form, NADP, are responsible for many of niacin's metabolic activities in your cells. In 1955, scientists discovered that nicotinic acid lowers blood cholesterol levels in humans.
Action
For decades, niacin's mechanism of action remained a mystery. In 2003, researchers working with drugmaker GlaxoSmithKline demonstrated that nicotinic acid stimulates a cellular receptor, designated HM74A, in fat cells and other tissues. This triggers changes in fatty acid metabolism and leads to several beneficial changes in blood lipid levels. Nicotinic acid therapy prompts a fall in total cholesterol, low-density lipoprotein cholesterol and triglyceride levels, while it increases high-density lipoprotein cholesterol levels.
Flushing
The most notable side effect of niacin therapy is a harmless but disagreeable flushing of the skin that can occur even at relatively low doses -- 50 to 100 mg. Flushing involves a dilation of the capillaries in your skin, followed by a burning sensation of your face and upper body. Nearly everyone who takes nicotinic acid experiences flushing. However, with repeated dosing, tolerance to this side effect develops within a few days. According to scientists at the University of Heidelberg in Germany, flushing results from stimulation of the same receptor -- HM74A -- that accounts for niacin's beneficial effects.
Dosing
Niacin is the most effective pharmaceutical agent for increasing your HDL cholesterol, according to an August 2002 "American Family Physician" review. LDL levels will fall 10 to 20 percent at doses of 1,500 to 4,500 mg per day. Individual response to niacin varies, but the majority of patients derive benefit by the time they reach 3,000 mg daily. Maximal changes in triglycerides and HDL cholesterol levels are typically seen at doses of 1,000 mg daily.
Considerations
To avoid the flushing associated with niacin therapy, start with low doses of immediate-release nicotinic acid -- 25 to 50 mg daily -- and rapidly escalate to 1,000 mg or more over several days. Alternatively, try an extended-release formulation, which causes less flushing. Taking an aspirin before your first daily niacin dose reduces flushing, as does taking niacin along with food. Over-the-counter preparations of nicotinic acid are available, but your doctor can offer a prescription formulation and advice on dosing.
References
- "World Journal of Diabetes"; Pharmacological Effects of Lipid-lowering Drugs on Circulating Adipokines; D. Wanders, et al.; September 2010
- "The Journal of Biological Chemistry"; Molecular Identification of High and Low Affinity Receptors for Nicotinic Acid; A. Wise, et al.; January 2003
- "The Journal of Clinical Investigation"; GPR109A (PUMA-G/HM74A) Mediates Nicotinic Acid-Induced Flushing; Z. Benyo, et al.; December 2005
- "American Family Physician"; High-risk Patients Need Tight Dyslipidemia Management; R. Sadovsky; August 2002
- "American Family Physician"; Combination Therapy Lowers LDL Levels; R. Sadovsky; April 2003
