The niacin flush (also called paresthesia) is an effect of supplementing with large amounts of niacin. Taking niacin at doses above 50 to 100 mg causes a pronounced flushing of the skin that results from activation of niacin receptors in the dermal Langerhans cells, something that generates prostaglandin D2 (PGD2) and prostaglandin E2 which then activate capillaries in the skin. This activation of capillaries causes an increased blood flow to the skin that is accompanied by warmth, itching and tingling. Tolerance develops quickly to niacin and decreases the degree of flushing because synthesis of prostaglandins that cause the flushing decrease and therefore this decreases the dilation of blood capillaries. Flushing with niacin can therefore be used as a rough measure of the state of fatty acids in cell membranes. This is because the prostaglandins produced by the action of niacin are synthesised from arachidonic acid (via the cyclooxygenase enzyme), a major omega-3 fatty acid in the cell membranes that is involved in inflammation. Studies show that human patients with low levels of arachidonic acid in their cell membranes also fail to show flushing, likely because the substrate for the prostaglandins necessary for flushing are not present in great enough concentrations. Further, patients who did not show signs of flushing can experience the effect if their levels of arachidonic acid in cell membranes are increased. Therefore niacin can be used as a basic test to understand the arachidonic acid content of cell membranes.
Eat Well, Stay Healthy, Protect Yourself
RdB
Glen, A. I. M., Cooper, S. J., Rybakowski, J., Vaddadi, K., Brayshaw, N. and Horrobin, D. F. 1996. Membrane fatty acids, niacin flushing and clinical parameters. Prostaglandins, Leukotrienes and Essential Fatty Acids. 55(1-2): 9-15
