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Dietary Reference Intakes
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Nutrition and Mental Health
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Niacin is a general term that refers to two forms of vitamin B3, nicotinic acid and niacinamide. Humans need niacin to remain healthy, and although the liver can slowly make very small amounts of niacin, most niacin must come from foods or dietary supplements.
Niacin deficiency is called pellagra. Pellagra affects the skin, digestive tract and brain. The best-known symptom is a rash that becomes darker when
(Illustration by GGS Information Services/Thomson Gale.)
exposed to light. In later stages, the digestive system may become inflamed, and finally the nervous system is affected.
Niacin is a necessary part of the cycle in which the body breaks down carbohydrates, fats, and proteins and converts them into energy. Niacin also plays a role in the production of certain hormones in the adrenal glands and in helping the liver remove harmful chemicals from the body.
Niacin belongs to the B-complex group of water-soluble vitamins. Scientists working with extracts of nicotine from tobacco first discovered nicotinic acid in the 1930s. Because nicotinic acid turned out to be a vitamin essential to health, scientists created the name niacin by using the first two letters of “nicotinic” and “acid” and the last two letters of “vitamin”. They did not want a health-promoting vitamin to be associated with nicotine and tobacco.
Normal niacin requirements
The United States Institute of Medicine (IOM) of the National Academy of Sciences has developed values called Dietary Reference Intakes (DRIs) for vitamins and minerals. The DRIs consist of three sets of numbers. The Recommended Dietary Allowance (RDA) defines the average daily amount of the nutrient needed to meet the health needs of 97-98% of the population. The Adequate Intake (AI) is an estimate set when there is not enough information to determine an RDA. The Tolerable Upper Intake Level (UL) is the average maximum amount that can be taken daily without risking negative side effects. The DRIs are calculated for children, adult men, adult women, pregnant women, and breastfeeding women.
The IOM has not set RDAs or ULs for niacin in children under one year old because of incomplete scientific information. Instead, it has set AI levels for this age group. RDAs and ULs for niacin are measured in micrograms (mg) of niacin equivalent (NE). One mg NE equals 1 mg niacin or 60 mg tryptophan, an amino acid that the liver can convert into niacin. Unlike the UL for many vitamins, the UL for niacin acid refers only to niacin that comes from fortified food or that is in dietary supplements such as multivitamins. There is no UL for niacin found in natural plant and animal foods. The UL for niacin also does not apply to individuals who are taking large doses of niacin under the supervision of a medical professional for the treatment of cardiovascular disease.
The following are the daily RDAs and IAs and ULs for niacin for healthy individuals:
Sources of niacin
Good sources of niacin include red meat, poultry, fish, and fortified cereals. A niacin fortification program began in the United States in 1938 when supplemental niacin was added to bread. Today niacin is routinely added to flour, cereals, bread, and pasta. These products can be labeled “fortified” or “enriched.” Because of niacin fortification, most healthy Americans get enough niacin from their diet without taking a dietary supplement. Niacin is also found in multivitamins, B-complex vitamins, and as a single-ingredient supplement.
Niacin is one of the more stable B vitamins and is not degraded or lost by exposure to heat, light, or air. The following list gives the approximate niacin content for some common foods:
Niacin, like other B-complex vitamins, is used in enzyme reactions that break down fats, carbohydrates, proteins, and alcohol into smaller molecules that can be used to produce energy or to build up different molecules necessary to create new cells. Most of the niacin a person needs must come from food. The liver does synthesize small amounts of niacin from tryptophan, an amino acid found in protein. However, this process is very slow, and it takes 60 mg of tryptophan to create 1 mg of niacin. Therefore, for humans to get enough niacin to maintain health, they must eat niacin-rich foods or take a dietary supplement containing niacin.
Diets that contain little or no niacin over time will result in a disorder called pellagra. Symptoms of pellagra include cracked, dry, scaly skin (pellagra means “rough skin” in Italian), swollen tongue, sore mouth, diarrhea, and mental changes. Left untreated, pellagra is fatal. Symptoms of less severe niacin deficiency include fatigue, mouth sores, vomiting, headache, depression, and memory loss.
Pellagra was common in the United States 1940s, particularly among poor people living in the South whose diet consisted mostly of corn and cornmeal. Corn contains niacin, but the niacin is bound to other molecules in a way that make it unavailable for use in the body. Many people in Mexico and Central America survive mainly on a diet of corn products. However, the tradition of soaking corn in solution containing alkaline lime before cooking releases the bound niacin so that it is available to the body. This explains why people living in Mexico and Central American rarely develop pellagra despite corn being a staple in their diet.
In 1938, the United States began a program to add niacin to bread. The fortification program resulted in a dramatic drop in the number of people developing pellagra. Today in the United States, those at highest risk of developing niacin deficiency are people with alcoholism, people with anorexia nervosa (self-starvation), and people with Hartnup's disease, rare genetic disorders that affect the ability of the body to absorb tryptophan.
Niacin and cardiovascular disease
Niacin in the form of nicotinic acid when taken in quantities as large as 2 grams three times a day has proved successful in rigorous clinical trials in lowering cholesterol levels in the blood and slowing the development of atherosclerosis (hardening of the arteries). When niacin is taken in these quantities, which are far beyond the established UL, it should be treated as a drug, not a dietary supplement, and taken only under the supervision of a physician. Sometimes niacin is prescribed along with statin (cholesterol lowering) drugs. This combination is often more successful in lowering cholesterol than either medication alone.
Over-the-counter niacin dietary supplements can be used to treat cardiovascular disease, but many physicians prefer high-dose prescription niacin. When sold as a prescription drug, the manufacturing process is more strictly controlled than it is for niacin sold as a dietary supplement. Niacin is available in a variety of immediate-, slow- or extended-release tablets or capsules and as a liquid. It is sold under many brand names including Niacor, Niaspan, Nicolar, Nic-otinex Elixir, Slo-niacin, and Novo-Niacin.
Niacin and other diseases
It must be emphasized that people who take high doses of niacin to lower cholesterol and improve cardiovascular health must treat niacin like a prescription drug and take it only under the direction of a physician. When high doses of niacin are prescribed, the dosage is increased gradually until the desired amount is reached in order to reduce unpleasant of side effects. Niacin should not be stopped suddenly without consulting a physician. Individuals who take large doses of niacin may need regular blood tests to determine the effectiveness of the treatment.
Studies on the safety of high doses of niacin during pregnancy have not been done. Niacin passes into breast milk and may cause unwanted side effects in breastfed babies. Pregnant and nursing women should consult their physician about whether to reduce or discontinue high-dose niacin supplements.
Niacin, especially at high doses, may interact with other drugs. Before starting niacin supplementation, patients should review with their physician all the prescription, over-the-counter, and herbal medications that they are taking. Some common drug interactions are:
When niacin is consumed within the established DRI range, complications are rare. However, when niacin is taken in therapeutic doses to treat disease, serious side effects may develop. The most common side effect is burning, tingling, or hot sensation in the face and chest along with flushed skin. This occurs most often at doses of 75 mg or higher. Building up slowly to large doses of niacin may reduce the sensation, as may taking aspirin 30 minutes before taking niacin. Other side effects include abdominal pain, dizziness, diarrhea, faintness, itchy skin, vomiting, unusual thirst, and irregular heartbeat. Liver damage may also occur at high doses.
Niacin deficiency almost never occurs in children, and niacin is not taken in large doses by children to prevent disease. When taken within established DRI ranges, parents should have few concerns about niacin.
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Tish Davidson, A.M.