Dukan Diet

Niacin Flush

Niacin is a B vitamin that is cheap and highly effective at raising HDL and lowering LDL. HDL and LDL were previously called good and bad cholesterol, resp., but since the data from numerous studies show that they don’t have a big impact on health, it is probably easier to just call them heavy and light reflecting less and more lipid content. If you still want to adjust your blood lipids, then niacin is more effective than the costly statins. Unfortunately, niacin also causes an uncomfortable (itchy and hot) flush.

The niacin flush is part of the inflammatory process that includes the classic tetrad of symptoms: rubor (redness), calor (increased heat), tumor (swelling), dolor (pain). Flushing in response to niacin shows that the immune cells in the skin respond to ingested niacin that is flowing through the capillaries. Mast cells in the skin have receptors that bind niacin and the cells secrete inflammatory prostaglandins. The prostaglandins act on the capillaries to cause dilation and flushing. Mast cells have secretory granules that fuse to the cytoplasmic membrane and release their contents outside. The granules contain histamine, heparin and tryptase. The histamine stimulates histamine receptors on pain/itch nerves and the tryptase stimulates receptors on a second set of pain/itch nerves.

Prostaglandins are produced by membrane bound enzymes on the surface of mast cells. When the mast cells are stimulated, additional enzymes are added to the surface through fusion of the secretory granules. The combined enzyme complex produces prostaglandins by releasing arachidonic acid (ARA) from phospholipids of the membrane (phospholipase A2, PLA2), converting the ARA to an epoxide prostaglandin (cyclooxygenase, COX-1) and stepwise producing additional prostaglandins. These prostaglandins cause the dilation of capillaries that is seen as flushing.

Niacin also binds to receptors on fat cells, adipocytes, and blocks release of fatty acids from the triglycerides stored in these cells. It is this action that is responsible for the increase in HDL and the lowering of LDL in blood serum.

An extension of the niacin skin flushing reaction is the use of this response to demonstrate the presence of arachidonic acid and a functional immune system in the skin. A recent study used topical application of niacin and skin reddening to test the idea that schizophrenia exhausts ARA as a result of inflammatory processes in the brain. Tests showed a tendency for schizophrenic episodes to be accompanied by a diminished flushing response to niacin. This result also suggests that a lowered system-wide ARA level should show up in a predisposition to gut problems.

It would be very interesting to test the interplay between inflammatory provocations, e.g. infection, serum omega-6/omega-3 fatty acids, and measures of inflammation, e.g. C-reactive protein on niacin flushing. Inflammatory depletion of ARA may be important in the decline in the integrity of tissues that is observed in inflammatory diseases of the gut (Helicobacter-based ulcers, IBD, Crohn’s disease, celiac), autoimmune diseases (arthritis, atherosclerosis), skin diseases (vitiligo), etc. It would also be interesting to test the impact of helminth infections to reverse ARA depletion.

reference:
Benyó Z, Gille A, Kero J, Csiky M, Suchánková MC, Nüsing RM, Moers A, Pfeffer K, Offermanns S. 2005. GPR109A (PUMA-G/HM74A) mediates nicotinic acid-induced flushing. J Clin Invest. 2005 Dec;115(12):3634-40.