Niacin, also known as nicotinic acid or vitamin B3, is a water-soluble vitamin whose
derivatives such as NADH play essential roles in energy metabolism in the living
cell. The designation vitamin B3 also includes the amide form, nicotinamide or
niacinamide. Severe lack of niacin causes the deficiency disease pellagra, whereas a
mild deficiency slows down the metabolism, which in turn decreases cold tolerance and
is a potential contributing factor towards obesity.
The name niacin derives from nicotinic acid + in. When the properties of niacin were
discovered, it was thought prudent to choose a common name other than nicotinic acid,
for fear that it might be confused with nicotine, leading to the ideas that either
smoking provided vitamins or that wholesome food contained a poison.
Nicotinic acid reacts with hemoglobin and myoglobin in meat to form a brightly
coloured complex, and thus has been used as a food additive, typically to improve the
colour of minced (ground) meat. However, sometimes excess niacin is added to the meat
during processing. Though still licensed as a food colouring agent in some countries,
it is not licensed as such in Europe.
The body can synthesize niacin from the essential amino acid tryptophan, but the
synthesis is extremely slow; 60 mg of tryptophan are required to make one milligram
of niacin. For this reason, eating lots of tryptophan is not an adequate substitute
for consuming niacin. As serotonin synthesis is reliant on tryptophan availability,
inadequate dietary intake of vitamin B3 may also therefore lead to
depression.
Because niacin in large quantities is a vasodilator, large doses of niacin (either
from vitamin B3 tablets or from treated meats) may cause harmless and short-lived but
unpleasant symptoms such as extreme skin flushing resembling a sunburn, itching,
gastric disturbances, and lowering of blood pressure. The amide form (strictly
speaking a provitamin) does not cause these side effects, but is also not as easily
assimilated by the body.
Large doses of niacin are sometimes prescribed to combat high blood pressure, and
also to lower blood cholesterol levels. Pharmacologic doses of niacin (1.5 to 6
grams/day) reduces LDL cholesterol levels by 10 to 25 percent and triglyceride levels
by 20 to 50 percent. HDL cholesterol levels are also increased by 15 to 35
percent.
Vitamin B3 has also been used to treat schizophrenia and other mental illnesses by
orthomolecular practitioners. Usually the nicotinamide form is used, as it is
considered to be more effective. Unfortunately there is little scientific evidence
that this treatment is effective.
.
|
