Niacin, or vitamin B3, is a water-soluble nutrient belonging to the B complex family. The term "niacin" is used to describe two chemically different substances, nicotinic acid and nicotinamide. Both of these compounds can be converted in your body to the active form of niacin, nicotinamide adenine dinucleotide, or NAD. NAD and its "phosphorylated" form, NADP, are responsible for most of niacin's metabolic effects, making them nutritionally equivalent. However, if you take niacin for lipid abnormalities, only nicotinic acid -- the form that causes flushing -- is effective. Your physician can guide your choice of niacin therapy.
Therapeutic Effects
Nicotinic acid has been used for decades to treat lipid disorders, such as high triglycerides. Lipid disorders are risk factors for atherosclerosis, or hardening of the arteries, which is the hallmark of coronary artery disease. According to the April 2008 issue of "The American Journal of Cardiology," nicotinic acid's beneficial effects on lipids are manifold. It lowers LDL cholesterol and triglyceride levels, increases HDL cholesterol levels and reduces inflammation in the walls of your arteries, all of which lessen your chance of developing heart disease.
Mechanism
Nicotinic acid exerts its effects on your lipid levels by attaching to a specific cellular receptor -- GPR109A -- in your fat tissue, thereby preventing the release of fatty acids and limiting their subsequent conversion to triglycerides. Decreased triglyceride synthesis leads to reduced LDL production in your liver and limits the breakdown of HDL, which results in desirable changes in your blood lipoprotein levels. (See Reference 1) Nicotinamide, by virtue of its slightly different molecular structure, does not affect lipid levels. Thus, nicotinic acid alone is useful for treating lipid disorders.
Flushing
Nicotinic acid therapy is often limited by its tendency to cause flushing, an unpleasant side effect characterized by redness, warmth and itching in your face and upper body. Scientists at the University of Pennsylvania report that flushing is partially attributable to stimulation of GPR109A receptors in your skin cells, which leads to release of inflammatory chemicals called prostaglandins and histamines. Efforts to develop niacin formulations that limit this inflammatory response have so far met with limited success.
Considerations
Nicotinic acid effectively lowers LDL and triglyceride levels and increases HDL levels, all of which reduce your risk of developing cardiovascular disease. However, many people shun nicotinic acid due to its side effects, which include liver toxicity, stomach irritation and flushing. Flushing is particularly troublesome with immediate-release preparations. Extended-release nicotinic acid formulations lessen flushing while maintaining niacin's therapeutic benefits. Nicotinamide, also known as niacinamide, is ineffective for correcting lipid abnormalities. Ask your doctor if niacin therapy is appropriate for you.
References
- "The American Journal of Cardiology"; Mechanism of Action of Niacin; V.S. Kamanna, M.L. Kashyap; April 2008
- "The Journal of Clinical Investigation"; Seeing Red: Flushing out Instigators of Niacin-Associated Skin Toxicity; R.L. Dunbar, J.M. Gelfand; August 2010
- "American Journal of Health-System Pharmacy"; Niacin for Dyslipidemia: Considerations in Product Selection: J. McKenney; May 2003
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