Water Soluble Vitamin: Niacin (vitamin B3)
Physiological Functions
Niacin is an essential vitamin that supports energy metabolism and reactions involving biosynthesis and degradation as part of the pyridine nucleotide coenzymes, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). The levels of oxidized and reduced forms of these coenzymes establish the redox potential in cells that regulates metabolic activities involving mitochondrial electron transport and numerous enzyme reactions.
High doses of niacin are also used as a pharmacological agent in blood lipid-lowering therapy.
Factors Affecting Availability
Because niacin is a water-soluble vitamin, significant amounts can be lost if large volumes of liquids are used in preparation and cooking of food sources. As with other B vitamins, niacin is lost in the milling of grains. To compensate for these losses, white flour and rice are enriched with the vitamin.
Niacin can be obtained from consumption of food sources or from biosynthesis with the amino acid tryptophan as a precursor. Approximately 60 mg tryptophan are required for synthesis of 1 mg of niacin. Niacin biosynthesis from tryptophan is dependent on availability of vitamin B6 and riboflavin.
Deficiency
Clinical evidence of niacin deficiency includes fatigue, poor appetite, diarrhea, irritability, headache, emotional instability and possible memory loss. Pellagra is the clinical manifestation of advanced niacin deficiency that is characterized by dermatitis, dementia, and diarrhea. Niacin deficiency rarely occurs without accompanying riboflavin deficiency. Pyridoxine deficiency may also be present.
Toxicity
Niacin toxicity is rarely observed at doses generally consumed. Administration of pharmacological doses of nicotinic acid (1-2 g three times a day) is used in treatment of high blood cholesterol. At this level of intake, histamine release may be triggered resulting in flushing of the skin which can be harmful to patients with asthma or peptic ulcer disease. Niacin also promotes hepatic toxicity when consumed at high doses found in some supplements.
The upper limit of safety for niacin established by the Food and Nutrition Board of the Institute of Medicine is 35 mg daily for adults. Niacin Tolerable Upper Intake Levels
Life Stage Niacin(mg)
Infants
0-6 months N/A
7-12 months N/A
Children
1-3 years 10
4-8 years 15
Males, Females
9-13 years 20
14-18 years 30
19-70 years 35
> 70 years 35
Pregnancy
< 18 years 30
19-50 years 35
Lactation
< 18 years 30
19-50 years 35
Requirements
The Daily Reference Intakes (DRI) for niacin are shown in the table below.
Life Stage Niacin (mg)
Infants
0-6 months 2
7-12 months 4
Children
1-3 years 6
4-8 years 8
Males
9-13 years 12
14-18 years 16
19-30 years 16
31-50 years 16
51-70 years 16
> 70 years 16
Females
9-13 years 12
14-18 years 14
19-30 years 14
31-50 years 14
51-70 years 14
> 70 14
Pregnancy
< 18 years 18
19-30 years 18
31-50 years 18
Lactation
> 18 years 17
19-30 years 17
31-50 years 17
Dietary Sources
Niacin is obtained from, liver, meat, peanuts and other nuts, and whole grains. In general, foods rich in protein, with exception of tryptophan-poor grains, can satisfy some of the demand for niacin. See the table below for dietary sources of niacin.
Dietary Sources of Niacin Food Niacin (mg) Beef liver, 3.5 oz cooked 14.4 Peanuts, 1/2 cup 10.5 Chicken, white meat, cooked 13.4 Tuna, canned in water, 3 oz 11.8 Salmon, 3.5 oz cooked 8.0 Corn grits, instant, 1 pkt 6.8 Ground beef, 3.5 oz cooked 5.3 Cheerios, 1 cup 5.0 Peanut butter, 2 Tbl 4.4 Almonds, 1/2 cup 1.4 Potato, baked with skin 3.3 Bagel, plain, 2.5 oz 3.3 Flour tortilla, 10" 2.6 Pasta, 1 cup cooked 2.3 Mushrooms, raw, 1/2 cup 1.7 Barley, 1/2 cup cooked 1.6 Corn, yellow, 1/2 cup 1.3 Mango, 1 medium 1.5 Lentils, 1/2 cup cooked 1.4 Sweet potatoes, 1/2 cooked 1.2 Peach, raw, medium .9 Carrot, raw, medium .7
