General Description
There are two basic forms of vitamin B-3, nicotinic acid (niacin)
and niacinamide. The body obtains niacin in two ways: it makes it
from the amino acid tryptophan, and it gets pure nicotinic acid
from foods. Nicotinic acid was discovered as a result of pellagra
epidemics in the southern United States at the turn of the 20th
century. The heavily corn-based diet of the South, at the time,
prevented an adequate dietary ingestion of the vitamin. Since 1939,
white flour has been enriched with nicotinic acid as a preventive
measure.
Food sources
Some good sources of vitamin B-3 are green vegetables, meat, poultry,
fish, whole-grain, enriched bread and cereal. Egg and milk don't
have much B-3, but they contain tryptophan, an amino acid which
the body can convert into nicotinic acid.
Health applications
Functions and uses
Niacin is essential for growth, for healthy tissues, and for the
conversion of carbohydrates into energy. It helps produce fats in
the body and it assists in processing alcohol. Vitamin B-3 acts
as a coenzyme in many cellular reactions, is involved in generating
energy for normal cellular function, and may be involved in the
processes by which skin pigments are made. Without niacin, thiamin
(B-1) and riboflavin (B-2) cannot function properly. Deficiencies
of niacin can cause pellagra and ailments of the skin, the digestive
system, and central nervous system.
Cataract
Clinical studies indicate that niacin may help prevent cataracts.1,2,3
Niacin, along with vitamin A, thiamin, and riboflavin, showed
positive results in preventing damage and cataract formation in
the nucleus of the lens.1 People between 65
and 74 may benefit the most from supplemental niacin for the prevention
of cataracts.2
High cholesterol
Niacin may reduce the risk of atherosclerosis and other cardiovascular
diseases by lowering LDL cholesterol and triglyceride levels with
the additional benefit of concomitantly raising HDL cholesterol
levels.4-6Clinical studies indicate that LDL
cholesterol levels decrease with large doses of niacin;7-9
however, such therapy needs to be closely monitored, as studies
also indicate that niacin therapy may cause hyperglycemia10
and mild to severe liver problems.6,10 Other
possibly mild complications such as flushing, itching, and rash
may also result from niacin therapy.8Cholesterol
management is often done with a form of niacin called inositol-hexaniacinate
("flush-free" niacin) which does not produce as many side effects.
Pellagra
Pellagra is believed to be a result of niacin deficiency. Alcoholics,
who are often nutrient deficient, and those limited to a corn
diet, (corn contains an unabsorbable form of niacin) are at an
increased risk of this classic vitamin B-3 deficiency. Symptoms
of pellagra include dermatitis, diarrhea, and dementia. Oral doses
of nicotinic acid are effective in the treatment of pellagra.11-13
Diabetes
Studies report that diabetics may benefit from niacin supplementation.14-17
Studies indicate that such supplementation reduces LDL cholesterol
and triglyceride levels without compromising glycemic control.15
An additional benefit of triglyceride reduction in diabetics is
that it may improve insulin sensitivity.16,17Most
often, diabetics are treated with the form of niacin called niacinamide.
Dosage and Toxicity
Normal dietary habits usually allow for an adequate intake of
this vitamin. Also, B-3 is often an ingredient in B-complex, or
multi-vitamin formulas. Niacin taken in excess of 50 mg daily
may cause flushing, stomachache, or headache. If taken in large
amounts, niacin can cause liver and eye damage, diabetes, gastritis
and gout; therefore, it is important that high intakes of niacin,
as used for therapeutic purposes, be closely monitored by a doctor
or nutritionist.
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