Niacin, also known as vitamin B3, is a water soluble vitamin comprised of nicotinic acid and niacinamide. It is involved in the utilization of proteins, fats and carbohydrates, and is needed for energy production in the body. It is necessary for the synthesis of fatty acids and the production of steroids. Niacin can be synthesized in the body from tryptophan. Niacin has been used since the 1950s for treatment of high cholesterol and other lipid abnormalities. It modulates all fats and lipoproteins, and favorably alters their quality and quantity. Niacin can be used alone or in combination with a cholesterol-lowering statin drug.
Mechanisms of Action
Recent research has brought a greater understanding of niacin's effect on lipid profiles. Its primary mechanism of action is to lower total cholesterol by reducing levels of low density lipoprotein, termed LDL or "bad" cholesterol, and very low density lipoprotein, called VLDL. According to a review of studies in the June 14, 2003 issue of the Journal of Nutritonal Biochemistry, niacin lowers total cholesterol primarily by an inhibitory effect on triglyceride mobilization and synthesis, resulting in a reduction in blood levels of LDL and VLDL particles. Even more benefit is conferred due to niacin's ability to increase the particle size of LDL, rendering them less harmful to blood vessels. In an article entitled, "The Effects of Niacin on Lipoprotein Subclass Distribution," by John M. Morgan, MD; Christina M. Carey, PA-C; Anne Lincoff, MD; and David M. Capuzzi, MD, PhD, the authors state that "niacin decreased the number of LDL particles by 15 percent at 1000 mg/d and by 23 percent at 2000 mg/d. Both dosages were also associated with significant increases in LDL particle size." Niacin also has favorable effects on lipid profiles by increasing blood levels of HDL, the "good" cholesterol.
Warnings
Although niacin is considered to be relatively safe in supplement form, caution must be used if taken as a cholesterol-lowering agent. Severe and life-threatening liver toxicity can occur. When taking doses greater than 1g per day, liver enzymes should be periodically monitored.
Both insulin- and non-insulin-dependent diabetics can develop elevated blood sugar when taking therapeutic doses of niacin. Therefore, close monitoring of blood sugar levels is necessary.
Niacin causes skin flushing, or vasodilatation, mediated by the prostaglandin system. This is a major drawback in its use, as many people find the heat and tingling of the niacin flush very uncomfortable. This flushing can be reduced by taking an extended-release form of niacin at bedtime.
Dose
Dosages are typically between 1 and 6 g per day in divided doses. Niacin should be started at a low dose and gradually increased over a period of weeks when using the immediate-release form. Niacin also comes in a no-flush form called inositol hexaniacinate, although data regarding its safety and efficacy are limited.
Dietary Sources
Rich sources of niacin are meats, fish, nuts, seeds and legumes. Most wheat flour products are fortified with niacin.
