VITAMIN B3 (Niacin, Nicotinic acid)
Vitamin B3 is a heat-stable member of the B VITAMIN complex needed by the body to extract ENERGY from FAT, CARBOHYDRATE and PROTEIN. Tissues convert niacin to two closely related COENZYMES (enzyme helpers): NICOTINAMIDE ADENINE DINUCLEOTIDE (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). NAD functions as an oxidizing agent used in processes that “‘burn” fuels to produce energy in the cell. These include the oxidation of GLUCOSE (GLYCOLYSIS) and of FATTY ACIDS. NAD transfers electrons to the mitochondrial ELECTRON TRANSPORT CHAIN, which ultimately reduces OXYGEN to water. This process liberates vast amounts of chemical energy trapped as ATP as well as releasing heat. NADP is generated from the oxidation of glucose (pentose phosphate pathway). The reduced form of NADP, NADPH, is used as a reducing agent in biosynthetic reactions rather than for energy production. CHOLESTEROL, fatty acids and other important compounds require NADPH for their synthesis. NADPH is also the basis of a powerful antioxidant system (GLUTATHIONE) to protect most cells from the damaging effects of highly reactive molecules called FREE RADICALS. NADPH also functions in the synthesis of DEOXYRIBOSE, the sugar building block of DNA.
Possible Roles of Niacin in Disease
PELLAGRA is a severe niacin deficiency disease that mimics schizophrenia. Skin rashes, DIARRHEA and mouth sores are prevalent in pellagra. At the turn of the century pellagra was epidemic in the southern United States among people whose diet was based on corn. By 1937 research demonstrated that niacin cured pellagra-like symptoms in dogs and, shortly thereafter, that niacin treatment cured pellagra. Niacin has been used in food fortification since 1941.
The use of niacin to treat schizophrenia and DEPRESSION is controversial. Generally negative results have been reported for patients with long-standing schizophrenia. Some clinicians reported improvement in patients with schizophrenia using megavitamin treatment with niacin or niacinamide, vitamin B6 and vitamin C and in patients with depression using niacinamide and tryptophan, together with taking steps to improve the diet. The American Psychological Association disapproved the use of niacin in the treatment of mental disorders in 1979.
Niacin may prevent HEART ATTACKS (a conclusion of the Coronary Drug Project Research Group). MEGADOSES of niacin (1 to 6 g daily) have been used to dramatically lower blood cholesterol and blood fat (triglyceride) levels, while increasing, HDL (HIGH-DENSITY LIPOPROTEIN, the desirable form of cholesterol) in patients with heart disease. Niacin reduces the risk of heart attacks for these reasons, and possibly niacin can reverse ATHEROSCLEROSIS. Niacin seems to increase the production of PROSTAGLANDINS. These hormone-like chemicals are produced locally within tissues to help control many physiologic processes such as BLOOD CLOTTING and INFLAMMATION.
Large doses of niacin may alleviate non-inflammatory ARTHRITIS, while low doses of niacin can relieve migraine headaches. Niacin supplements may help normalize blood sugar in patients with hypoglycemia. Large doses of niacin may prevent harmful effects of chemical pollutants, drugs and alcohol, and may help during recovery and drug rehabilitation (the mechanism is not known). This is a promising area of research, but presently niacin cannot be claimed to be a broad-spectrum detoxification agent.
Good sources of niacin are EGGS, MEAT (especially liver), fish, POULTRY and unprocessed food, including peanuts and potatoes. Coffee provides about 3 mg per cup. Niacin is one of the commonly fortified nutrients; consequently, enriched flour and cereals are good sources. MILK and CHEESE are good sources because they contain large amounts of the essential AMINO ACID, TRYPTOPHAN, which is partially converted by the body to niacin. Protein-deficient diets are often related to pellagra. This explains why diets incorporating milk can prevent or cure pellagra.
The form available from animal foods is NIACINAMIDE, a derivative of niacin; plant foods provide niacin itself. Niacin is one of the most stable of the B vitamins: It resists most cooking procedures and can be stored in the dry state indefinitely without loss. Canning, DEHYDRATION and exposure to air or light cause little destruction.
Up to 70% of the niacin in most cereal grains, including corn is present as a bound form called niacytin. It is not released during digestion and therefore is poorly absorbed. Traditionally, corn tortillas are prepared from corn pretreated with limewater to improve dough consistency, a treatment that also frees niacin. Pellagra is uncommon in Mexico, Central and South America, where corn is soaked in lime. Presently niacin deficiency and pellagra are common only in certain regions of Africa and Asia, where corn is a major source of protein. Because niacin is so prevalent in high-quality protein, only alcoholics and heavy drinkers are likely to be deficient in the United States. Symptoms of, mild deficiency include apathy, headache, irritability and memory loss.
The RECOMMENDED DIETARY ALLOWANCE for healthy adult men is 19 mg; for non-pregnant, non-lactating women it is 15 Mg. The daily niacin requirement varies with the number of calories burned daily (the energy expenditure) and the protein intake. One niacin equivalent equals 1 mg of preformed niacin or 60 mg of dietary tryptophan.
Niacin can be synthesized in the body from the essential amino acid tryptophan. Tissues can form an average of I mg of niacin from 60 mg of tryptophan provided by dietary protein. Consequently a high-quality protein diet supplies substantial tryptophan for niacin synthesis. On the other hand, a protein-deficient diet or a diet relying on low tryptophan protein increases the dietary requirement for niacin. Most animal protein contains 1.4% tryptophan; vegetable protein, 1%; and corn protein, only 0.6%.
Niacin (but not closely related niacinamide) expands CAPILLARIES and can lead to itching and flushing at doses commonly used in multivitamin supplements (100 mg or more). While nausea, diarrhea and flushing may accompany niacin usage; these side effects are not considered dangerous. Excessive niacin can cause irregular heartbeat, cramps, headache and liver inflammation. “”Sustained release”‘ niacin may cause less flushing, but some preparations may be more toxic to the liver. Other forms, such as inositol hexaniacinate, may improve niacin therapy. Large doses of niacin can increase BLOOD SUGAR in diabetics, increase the risk of GOUT and aggravate ulcers. Niacin supplements are not recommended for those with PEPTIC ULCERS, COLITIS, ASTHMA, liver disease, GOUT or erratic heartbeat. Using niacin therapeutically (1,000 mg or more per day) requires medical supervision; liver function and blood sugar need to be monitored.
Di Palma, J.R. and Thayer, W.S., “‘Use of Niacin as a Drug,” Annual Review of Nutrition, 11 (1991), pp. 169-87.
Niacinamide (nicotinamide) is a derivative of the water-soluble vitamin NIACIN. Niacinamide is readily formed in the body from niacin and incorporated into two important COENZYMES (enzyme helpers): NICOTINAMIDE ADENINE DINUCLEOTIDE (NAD) and its phosphate-containing analog, nicotinamide adenine dinucleotide phosphate (NADP). By assisting in oxidation-reduction reactions, NAD performs an essential role in energy production from nutrients. NAD is required by all cells in many aspects of metabolism, including CARBOHYDRATE, FATTY ACID and AMINO ACID degradation. The reduced form of NADP, NADPH, participates in reductions required for biosynthesis.
Niacinamide is the most prevalent form of this vitamin in animal products and MEAT, although niacin is more prevalent in plant foods. Niacinamide lacks the capillary expanding (skin-flushing) activity of niacin and is somewhat safer than niacin; hence it is more often used when large amounts of the vitamin are required. Side effects of niacinamide include nausea, headache, fatigue, and sore mouth. Large amounts can injure the liver (jaundice).