Nicotinamide is the most common form of the vitamin niacin. Nicotinamide is found in the body as part of nicotinamide adenine dinucleotide (NAD), an important cofactor of many enzymes involved in metabolism and the production of energy from sugars and fats. The structure of nicotinamide, shown in Figure 1, incorporates a six-atom ring, with one nitrogen atom in the ring and another in the amide group side chain. Nicotinic acid is the other common form of niacin. It has the same ring structure but, as shown in Figure 2, oxygen atoms replace the nitrogen atom in the side chain. The nicotinic acid form of the vitamin produces severe side effects when taken in large doses; however, it is sometimes used as a medication to reduce high cholesterol levels in blood. Nicotinic acid was first produced from nicotine long before it was known to be a nutrient. Despite the similarities between nicotine and nicotinic acid, their functions are very different.
Niacin and Pellagra
Pellagra is a disease characterized by skin rashes, diarrhea, mental deterioration, and death. Early in the last century it was a serious health problem. Alan Kraut in "Dr. Joseph Goldberger & the War on Pellagra" describes the situation as follows. In 1912 South Carolina alone reported 30,000 cases of pellagra and a mortality rate of 40 percent. In 1914 Dr. Joseph Goldberger (1874–1929) was assigned to study the disease. Goldberger had extensive prior experience treating yellow fever, dengue fever, and typhus. He noted that unlike these other diseases, pellagra was never transmitted from patients to doctors or hospital staff. He also determined that those patients likely to exhibit symptoms of pellagra shared a diet of refined corn flour, molasses, and pork fat. Such observations led Goldberger to deduce that poor nutrition might be the cause of the disease. In 1915 he tested his hypothesis with volunteers from a Mississippi prison. They were fed only the suspect diet and half developed the signs of pellagra within a few months. The symptoms disappeared when meat and vegetables were added to the volunteers' diet. Despite the fact that his study clearly indicated poor nutrition was the cause of pellagra, Goldberger spent the rest of his career attempting to convince political and medical authorities that germs were not the root cause of this dreaded disease. He was perhaps hampered in his efforts by the inability to determine exactly what was missing in the diet. Not until 1937 did Conrad Elvehjem identify the chemical nicotinamide as the cure for pellagra in dogs, followed almost immediately by the work of Thomas Spies, who demonstrated that niacin also cures human pellagra.
Sources of Niacin
The Federal Enrichment Act of 1942 required the millers of flour to restore iron, niacin, thiamin and riboflavin lost in the milling process. Enriched flours and baked goods made from them are now excellent sources of niacin. Niacin may also be found in meat, poultry, fish, whole grains, and peanut butter. Besides direct niacin intake, humans can convert the amino acid tryptophan to niacin. Many people take daily vitamin supplements to ensure they get enough niacin and other essential nutrients.
Anderson, Jean, and Barbara Deskins. The Nutrition Bible. New York: William Morrow and Co., 1995.
Kraut, Alan. "Dr. Joseph Goldberger & the War on Pellagra." Available from http://www.nih.gov/od/museum/exhibits/goldberger/full-text.html .