Niacin - Vitamin B3

Niacin is one of the water-soluble B vitamins. Niacin is the generic name for nicotinic acid (pyridine-3-carboxylic acid), nicotinamide (niacinamide or pyridine-3-carboxamide), and related derivatives, such as nicotinamide riboside. Niacin is naturally present in many foods, added to some food products, and available as a dietary supplement.

All tissues in the body convert absorbed niacin into its main metabolically active form, the coenzyme nicotinamide adenine dinucleotide (NAD). More than 400 enzymes require NAD to catalyze reactions in the body, which is more than for any other vitamin-derived coenzyme. NAD is also converted into another active form, the coenzyme nicotinamide adenine dinucleotide phosphate (NADP), in all tissues except skeletal muscle. NAD and NADP are required in most metabolic redox processes in cells where substrates are oxidized or reduced. NAD is primarily involved in catabolic reactions that transfer the potential energy in carbohydrates, fats, and proteins to adenosine triphosphate (ATP), the cell’s primary energy currency. NAD is also required for enzymes involved in critical cellular functions, such as the maintenance of genome integrity, control of gene expression, and cellular communication. NADP, in contrast, enables anabolic reactions, such as the synthesis of cholesterol and fatty acids, and plays a critical role in maintaining cellular antioxidant function.

Most dietary niacin is in the form of nicotinic acid and nicotinamide, but some foods contain small amounts of NAD and NADP. The body also converts some tryptophan, an amino acid in protein, to NAD, so tryptophan is considered a dietary source of niacin.

When NAD and NADP are consumed in foods, they are converted to nicotinamide in the gut and then absorbed. Ingested niacin is absorbed primarily in the small intestine, but some is absorbed in the stomach.

Even when taken in very high doses of 3 - 4 g, niacin is almost completely absorbed. Once absorbed, physiologic amounts of niacin are metabolized to NAD. Some excess niacin is taken up by red blood cells to form a circulating reserve pool. The liver methylates any remaining excess to N1-methyl-nicotinamide, N1-methyl-2-pyridone-5-carboxamide, and other pyridone oxidation products, which are then excreted in the urine. Unmetabolized nicotinic acid and nicotinamide might be present in the urine as well when niacin intakes are very high.

Recommended Amounts
The amount of niacin you need depends on your age and sex. Average daily recommended amounts are listed below in milligrams (mg) of niacin equivalents (NE) (except for infants in their first 6 months).

The mg NE measure is used because your body can also make niacin from tryptophan, an amino acid in proteins. For example, when you eat turkey, which is high in tryptophan, some of this amino acid is converted to niacin in your liver. Using mg NE accounts for both the niacin you consume and the niacin your body makes from tryptophan. Infants in their first 6 months do not make much niacin from tryptophan.

1. RDA - Recommended Amounts:- Birth to 6 months: 2 mg
- Infants 7–12 months: 4 mg NE
- Children 1–3 years: 6 mg NE
- Children 4–8 years: 8 mg NE
- Children 9–13 years: 12 mg NE
- Teen boys 14–18 years: 16 mg NE
- Teen girls 14–18 years: 14 mg NE
- Adult men 19+ years: 16 mg NE
- Adult women 19+ years: 14 mg NE
- Pregnant teens and women: 18 mg NE
- Breastfeeding teens and women: 17 mg NE

2. UL - Upper Intake Level: The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health.
- Birth to 12 months: Not established
- Children 1–3 years: 10 mg
- Children 4–8 years: 15 mg
- Children 9–13 years: 20 mg
- Teens 14–18 years: 30 mg
- Adults 19+ years: 35 mg

How harmful is if excess Niacin?
Toxicity when eating foods containing niacin is rare, but can occur from long-term use of high-dose supplements. A reddened skin flush with itchiness or tingling on the face, arms, and chest is a common sign. Flushing occurs mainly when taking high-dosage supplements in the form of nicotinic acid, rather than nicotinamide. Niacin taken in large doses as supplements may also increase uric acid levels, which is a risk factor for gout. Other signs: Dizziness, Low blood pressure, Fatigue, Headache, Upset stomach, Nausea, Blurred vision. Impaired glucose tolerance and inflammation of liver in severe cases (at very high doses of 3,000-9,000 mg daily for several months/years).

What happens if deficiency in Niacin?
A niacin deficiency is rare in the United States and other industrialized countries because it is well-absorbed from most foods (with the exception of some cereal grains in which niacin is bound to its fibers, decreasing the absorption) and is added to many foods and multivitamins. A severe niacin deficiency leads to pellagra, a condition that causes a dark, sometimes scaly rash to develop on skin areas exposed to sunlight; bright redness of the tongue; and constipation/diarrhea. Other signs of severe niacin deficiency include: Depression, Headache, Fatigue, Memory loss, Hallucinations.

Groups at risk for deficiency
1. Limited dietsPeople whose diets are limited in both variety and quantity of foods, such as those living in poverty or who are very ill and cannot eat a balanced diet, are at increased risk. Developing countries that eat corn or maize as a main food source are at risk for pellagra, as these foods are low in both absorbable niacin and tryptophan.

2. Chronic alcoholism The absorption of several nutrients, particularly water-soluble vitamins including the B family, is decreased with excessive alcohol intake.

3. Carcinoid syndromeThis is a disease of slow-growing cancer cells in the gut that release a chemical called serotonin. The syndrome causes tryptophan in the diet to be converted into serotonin rather than niacin, which increases the risk of decreased niacin.

Food Sources
A niacin deficiency is rare because it is found in many foods, both from animals and plants.
- Red meat: beef, beef liver, pork
- Poultry
- Fish
- Brown rice
- Fortified cereals and breads
- Nuts, seeds
- Legumes
- Bananas, avocado

Niacin and Health
1. Cardiovascular diseaseFor more than 40 years, niacin in the form of nicotinic acid has been given to patients to treat a condition called dyslipidemia, a major risk factor for cardiovascular diseases (CVD) such as coronary artery disease, heart attack, and strokes. Bloodwork in someone with dyslipidemia may show high total and LDL “bad” cholesterol levels, low HDL “good” cholesterol, and elevated triglycerides.

Nicotinic acid supplements contain high amounts, up to 1,000-2,000 mg of niacin taken daily. Studies have shown that they can increase HDL cholesterol and lower LDL cholesterol and triglycerides. However, negative side effects (skin flushing, stomach upset, diarrhea) usually accompany the supplements, resulting in poor compliance from patients. Clinical trials have not consistently shown that nicotinic acid leads to less cardiovascular events or deaths from CVD.

Though earlier clinical trials showed a reduction in CVD events and deaths with niacin therapy, two more recent large clinical trials on CVD outcomes concluded differently. Both were large randomized placebo-controlled trials, following participants for up to 4 years. Niacin supplements were given (1,500-2,000 mg daily), alone in one trial and with a statin medication in the other. Both trials concluded that taking niacin supplements did not show benefit. The niacin/statin trial did not show a reduction in strokes, heart attack, or CVD deaths despite significant improvements in HDL cholesterol and triglyceride levels. The niacin supplement-only trial did not find a reduction in CVD events and also noted a significant increase in adverse reactions compared with the placebo group, including increased incidence of type 2 diabetes, gastrointestinal bleeding and ulcers, and diarrhea. A Cochrane review of 23 randomized controlled trials on nicotinic acid supplements for the prevention of CVD events found that the supplements did not reduce overall deaths, CVD deaths, heart attacks, and strokes, and was associated with negative side effects. The results of these and other cardiovascular outcome trials led the U.S. Food and Drug Administration (FDA) to conclude that the “scientific evidence no longer supports the conclusion that a drug-induced reduction in triglyceride levels and/or increase in HDL-cholesterol levels in statin-treated patients results in a reduction in the risk of cardiovascular events.” Along with that conclusion, the FDA stated that the benefits of niacin extended-release tablets and fenofibric acid capsules taken with statins no longer outweighed the risks, and should not be recommended.

2. Cognitive healthA severe niacin deficiency has been associated with cognitive decline such as memory loss and dementia. Niacin is believed to protect brain cells from stress and injury. It is not yet clear though if smaller variations in dietary niacin intake can negatively affect brain function.

A large prospective study of 3,718 men and women ages 65 and older were followed for 6 years, using dietary questionnaires and cognitive assessments. A protective effect from Alzheimer’s disease and cognitive decline was found when comparing the highest to lowest intakes of niacin.

The Coronary Artery Risk Development in Young Adults (CARDIA) study followed 3,136 men and women ages 18-30 for up to 25 years. The study measured dietary and supplemental B vitamin intake and cognitive function. A higher intake of B vitamins, but particularly niacin, throughout young adulthood was associated with better cognitive function scores in midlife. However, cognitive function was only assessed at the end of the study, so any changes in cognitive function over time was not known. Research in this area is limited but there are several clinical trials underway that may shed further light on niacin’s effects on brain health.

Did you know?
Many B vitamins are thought to help increase energy, including niacin. Because niacin is water-soluble (less risk of building up in the body to a toxic level), many people don’t think twice about taking a supplement that may contain 100 times the RDA for the vitamin. Although niacin assists several enzymes in converting food into ATP, a form of energy, taking doses well beyond the RDA will not offer a special boost in energy levels. Eating a balanced diet with a variety of foods is often all that is needed to obtain niacin’s energy-boosting benefit.

Corn is naturally high in niacin, but it is bound to carbohydrates which makes it difficult for the human body to absorb. However, when corn is nixtamalized (a traditional process in tortilla making where corn is treated with calcium hydroxide, cooked, and ground) the niacin becomes absorbable because of the calcium hydroxide treatment.

Compiled and written by Crocus Media