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(NIACIN)
DESCRIPTION
Niacin (Vitamin B-3) is a water-soluble vitamin required
by all living cells. It functions in the release of energy from carbohydrates,
fats, and proteins. Niacin is also involved in the synthesis of protein, fat,
and pentoses needed for nucleic acid formation.
Niacin is a major constituent of the coenzyme
nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide
phosphate (NADP). These compounds function to remove hydrogen atoms during
biological reactions.
METHOD OF ACTION
Niacin is absorbed in the intestine; little is stored in
the body and any excess of the vitamin is excreted in the urine.
Niacin functions as a component of the coenzymes
nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide
phosphate (NADP). These enzymes are involved in respiration where they act as
hydrogen acceptors. They are essential in the reactions involved in the release
of energy from carbohydrates, fats, and proteins.
Niacin can be synthesized in the body from tryptophan.
Only the L-isomer of tryptophan can be converted into niacin, and the
conversion requires the presence of thiamine, pyridoxine, and riboflavin.
Niacin is stable to heat, light, acid and alkali;
therefore, little is lost during processing. Vitamin B-Complex, vitamin B-1,
Vitamin B-2, Vitamin C, and phosphorus assist the absorption of niacin.
Alcohol, coffee, corn, sugar, starches, and excess carbohydrates prevent
absorption.
PROPERTIES AND USES
The major clinical application of niacin is in the
treatment of pellagra.
There is also evidence which suggest that doses of one to
two grams of niacin three times per day may result in lowered blood cholesterol
levels. This may protect against recurrent nonfatal heart attacks.
Large doses of niacin have also been used to treat
schizophrenia. Orthomolecular therapy, using extremely large amounts of
vitamins, is a controversial treatment of psychiatric problems, as critics say
that not enough scientific evidence exists to support the claims made. Since
the ingestion of large therapeutic amounts of nicotinic acid usually produces a
flushing reaction, niacin prescribed for nutritional deficiency is frequently
taken as nicotinamide, though the benefits and reactions are not identical to
the nicotinic acid form of niacin.
Niacin deficiency is also common in
alcoholics. Low levels of niacin are also seen in patients with chronic hepatic
failure.
CONSEQUENCES OF DEFICIENCY
There are many symptoms of niacin
deficiency. Initially, muscular weakness, anorexia, indigestion, and skin
eruptions occur, with severe deficiencies of niacin commonly leading to
pellagra. Symptoms of pellagra include dermatitis, senile dementia, and
diarrhea. Tremors and a sore tongue are also symptomatic. With pellagra, the
skin becomes cracked and pigmented in the parts exposed to sunlight. Lesions
can appear in the central nervous system, producing confusion, disorientation
and neuritis. Inflammation of the mucous membranes of the mouth and the
gastrointestinal tract can result from digestive abnormalities developed in
niacin deficiency. Symptoms of severe riboflavin deficiency appear; many of the
niacin deficiencies are similar due to the close interrelationship of
riboflavin and niacin in cell metabolism.
Often, people who suffer from pellagra
are on very inadequate diets in which corn is a main foodstuff. Such a diet
contains little niacin, while the tryptophan in the corn is unavailable and
cannot be absorbed from the intestine. Thus, there is no tryptophan available
for conversion to niacin and niacin deciency results.
Presoaking corn in lye makes tryptophan
available for absorption, due to the presence of alkali.
TOXICITY FACTORS
No real toxic effects of niacin are known. However, large
doses cause side effects such as: a tingling sensation, flushing of the skin,
gastrointestinal distress, unusual nervousness, and glucose intolerance.
RECOMMENDED DIETARY ALLOWANCES
Niacin requirements are affected by such factors as:
aging, growth periods, body size, physical activity, illness, tissue trauma,
pregnancy and lactation. The RDA standard, 6.6 mg per 1,000 kilocalories (but
not less than 13 niacin equivalents at intakes of less than 2,000
kilocalories), is about 50% higher than the minimum requirement; this is in
order to provide a safety margin to cover variances in individual need. These
recommendations also allow for the contribution of tryptophan, in terms of
niacin equivalents, from dietary protein sources. The daily allowance of
vitamin B-3 should be based on caloric intake.
RDA for men - 19 mg
RDA for women - 15 mg
RDA for children 7 to Years - 13 mg
RDA for infants - 6 mg
RDA for pregnant and lactating women - 20 mg
Note: It is recognized that one milligram of niacin is
derived from each 60 mg of dietary tryptophan.
Food Sources
· Organ Meats
· Halibut
· Rice Bran
· Tuna
· Brewer's Yeast
· Roasted Peanuts
· Swordfish
· Nuts
· Brown Rice
· Corn
· Broccoli
· Avocados
· Dates
· Figs
· Green Peas
· Lima Beans
· Mushrooms
· Wheat/Wheat Germ
· Potatoes
· Parsley
· Swiss Cheese
SUMMARY OF B-3 NIACIN DEFICIENCY
SYMPTOMS:
· Pellagra
· Dermatitis, Diarrhea, and Dementia
· Muscular Weakness
· General Fatigue
· Anorexia
· Indigestion
· Insomnia
· Irritability
· Stress
· Depression
· Schizophrenia
· Excessive Blood Cholesterol
· Poor Learning Ability
· Arthritis and Joint Malfunctions
· Gastrointestinal Upsets Such As:
· Nausea
· Vomiting
· Inflammation of Mouth and Digestive Track
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