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B3

Description

Niacin (Vitamin B3), a member of the B vitamin family, is the term used for both nicotinic acid and nicotinamide. These two compounds have identical vitamin activities but are different in their pharmacological activities. Nicotinic acid, in pharmacological doses, is used as an antihyperlipidemic agent while nicotinamide may have anti-diabetogenic activity. Niacin is active as nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP), which serve as coenzymes. Niacin is water-soluble, stable under acidic and alkali conditions and resistant to light and oxidation. Niacin's biochemical effects are principally mediated by its metabolite nicotinamide adenine dinucleotide (NAD+). Both nicotinic acid and nicotinamide are efficiently absorbed from the stomach and small intestine with almost complete absorption of doses up to 3-4 g. Tryptophan is converted to niacin with 60 mg of tryptophan equivalent to 1mg of niacin. This is termed niacin equivalent.

Functions

Niacin, through its metabolites, is involved in a variety of biological processes including:

Energy production; NAD+, a niacin metabolite, is used in metabolic reactions to transfer the potential free energy stored in carbohydrate, fat and protein to NADH, which is used to form ATP.

The regulation of gene expression and the maintenance of genomic activity.

Synthesis of fatty acids, cholesterol and steroids, NADPH (the reduced form of NADP+), serves as the reducing agent in fatty acid and steroid biosyntheses. It also serves to maintain glutathione in its reduced form.

NAD+ and NADP+ are both involved in the biosyntheses of signaling molecules.

Dietary sources

Niacin and its precursors are found naturally in meat, poultry, fish, legumes and yeast.

Required Intakes

Age mg/day TolerableUpper Intake Levels(UL)
0 to 6 months 2* ND
7 to 12 months 4* ND
1 to 3 years 6 10
4 to 8 years 8 15
9 to 13 years 12 20
Male 14 to18 years 16 30
Male 19 + years 16 35
Female 14 to 18 years 14 30
Female 19 + years 14 35
Pregnancy to 18 years 18 30
Pregnancy 19 to 50 years 18 35
Lactation to 18 years 17 30
Lactation 19 to 50 years 17 35

* Values are Adequate Intakes (AI), others are RDA.DRI for niacin based on niacin equivalents (NE); 1 mg niacin = 60 mg tryptophan; 0 - 6 months is preformed niacin and not NE.ND: Not determinable due to lack of data of adverse effects in this age group and concern with regard to lack of ability to handle excess amounts.

Cautions

Take niacin supplements with meals or a glass of milk to prevent stomach discomfort.

Niacin acts like a drug when taken in high doses (1.5 to 6 grams a day). If you're contemplating using niacin in this dosage range, consult a doctor for supervision.

When possible, substitute inositol hexaniacinate for niacinamide and nicotinic acid. Inositol hexaniacinate is the safest form available, causing no skin flushing and posing considerably less risk of liver damage.

Use caution when taking large, therapeutic doses of niacin--in any form--if you're already on one of the cholesterol-lowering prescription drugs known as statins. Muscle pain and inflammation, and even kidney failure, are a risk if you mix niacin with any of the statins. Stop taking the drug and call your doctor immediately if any of the above symptoms occur.

Check with your doctor before taking niacin if you suffer from diabetes, low blood pressure, glaucoma, gout, liver disease, ulcers or a bleeding disorder. Niacin supplements may aggravate these conditions.

Have your doctor schedule blood tests every three months to check liver function if you take any form of niacin in amounts of 1,000 mg or more daily.

Don't take timed-release niacin, an over-the-counter cholesterol drug designed specifically not to cause nicotinic acid-related skin flushing. Research indicates it may cause liver damage.

Stick to recommended doses; excessive amounts can cause serious health problems.