although vitamin A deficiency severe enough to
cause such disruptions is rare. Other consequences
of vitamin A deficiency generally improve when
levels of vitamin A return to normal.
Vitamin A toxicity nearly always results from
taking high doses of vitamin A supplement and can
occur as acute OVERDOSE(taking an extremely large
dose at one time) or chronic overdose (excess that
accumulates over time), usually the result of over-
supplementation. Treatment with retinol medica-
tions, such as for severe ACNE, also can result in
vitamin A toxicity. In adults the effects and symp-
toms of vitamin A toxicity are reversible and gener-
ally resolve within a few weeks of stopping
supplementation or therapeutic retinol.
Vitamin B Complex
The eight B vitamins, called the vitamin B com-
plex, work in close synchronization with one
another and have key roles in many functions in
the body. Each B vitamin further has specific func-
tions, dietary sources, deficiency level, and toxic-
ity level. In general the B vitamins are essential
for energy conversion (metabolism of carbohy-
drates and fats) and other functions of cellular
metabolism, erythropoiesis (making new red
blood cells), and maintaining the epithelium (skin
and mucous membranes). The liver stores some of
the B vitamins for a short time. Food sources of
the B vitamins include meats, poultry, fish, eggs,
leafy green vegetables, fruits, whole grains, brown
rice, and fortified grain products such as cereals
and breads (regulations in the United States
require such fortification).
Deficiencies of B vitamins affect many func-
tions of the body. Most often deficiencies of the B
vitamins occur collectively, though specific defi-
ciency disorders are BERIBERI(thiamine deficiency),
PELLAGRA(niacin deficiency), and pernicious ANE-
MIA (cyanocobalamin deficiency). In the United
States vitamin B deficiencies generally result from
chronic health disorders, ALCOHOLISM, and MALAB-
SORPTIONdisorders. In such circumstances it often
is necessary for the person to take therapeutic
vitamin B supplements, either B complex or spe-
cific B vitamins, to compensate.
Toxicity of B vitamins is uncommon though
can occur when taking excessive vitamin supple-
ments and in some metabolic disorders; it is most
likely to develop with niacin (B 3 ), pantothenic
acid (B 5 ), pyridoxine (B 6 ), and folic acid (B 9 ).
Though most symptoms resolve when vitamin B
intake returns to normal, vitamin B toxicities can
result in permanent neurologic and skin damage.
Vitamin B 1 (thiamine) Thiamine converts car-
bohydrates into GLUCOSEand is a coenzyme in the
synthesis of acetylcholine, a NEUROTRANSMITTER
important for cognitive functions in the cerebral
cortex and MUSCLEcoordination throughout the
body. Prolonged thiamine deficiency causes
beriberi.
Vitamin B 2 (riboflavin) Riboflavin is a key
player in macronutrient metabolism (fats, carbo-
hydrate, and proteins) as well as in energy con-
version at the cellular level (cellular oxidation). It
is essential for growth and development in chil-
dren, facilitates erythropoiesis (formation of new
red blood cells), and helps support the health of
the retina.
Vitamin B 3 (niacin)Niacin exists in two forms:
nicotinic acid and niacinamide (also called nico-
tinamide). In either form it facilitates the metabo-
lism of carbohydrates (glycolysis) and functions of
cellular energy conversion. Niacin also helps
maintain the structure of the epithelium (skin and
mucous membranes). The body synthesizes some
niacin from the essential amino acid tryptophan.
Prolonged niacin deficiency causes pellagra. Niacin
has emerged as an effective therapy for mild to
moderate HYPERLIPIDEMIA, reducing CHOLESTEROL
BLOOD LEVELSas effectively as some lipid-lowering
medications.
Vitamin B 5 (pantothenic acid) Pantothenic
acid is essential for metabolizing amino acids and
fats to carbohydrates, and works in collaboration
with folic acid and biotin for various functions
related to cellular energy conversion. The liver
uses pantothenic acid in the synthesis of hor-
mones and cholesterol. Canning and freezing
destroy pantothenic acid.
Vitamin B 6 (pyridoxine) Pyridoxine facilitates
HEMOGLOBINproduction, conversion of tryptophan
to niacin, and carbohydrate metabolism. Other
forms of vitamin B 6 are pyridoxal and pyridox-
amine; all forms of vitamin B 6 convert to the
coenzyme pyridoxal-5'-phosphate (PLP) in the
body. Health conditions that increase the body’s
specific use of and need for pyridoxine includevitamins and health 205