vitamin C supplementation for people recovering
from major surgery, serious burns, and significant
dental procedures.
Vitamin D (Calciferol)
Without vitamin D, the body cannot use calcium.
Vitamin D is unique among vitamins in that the
body can manufacture it as a process of photosyn-
thesis (exposure to sunlight) that converts a form
of cholesterol stored in the cells of the skin into
vitamin D. Only a small portion of vitamin D
enters the body from dietary sources (namely, for-
tified dairy products) in the form of vitamin D 2
(ergocalciferol) or vitamin D 3 (cholecalciferol).
The circulating, active form of vitamin D is cal-
citriol, which functions as a HORMONE. Calcitriol, in
tandem with PARATHYROID HORMONE, regulates the
amount of calcium in the blood. This regulation
determines the availability of calcium to the
bones. Vitamin D also influences IMMUNE SYSTEM
functions important for fighting tumors.
Vitamin D deficiency affects bone structure,
preventing bone tissue from accepting new cal-
cium and allowing calcium to leave the bones to
enter the blood circulation. Vitamin D deficiency
can cause rickets in children and OSTEOMALACIAin
adults. Both are conditions of demineralization
that are reversible with vitamin D supplementa-
tion, though severe rickets may result in residual
deformity particularly of the pelvis. Sustained
vitamin D deficiency in adults leads to OSTEOPORO-
SIS, an irreversible loss of bone tissue.
Vitamin D toxicity may develop with excessive
consumption from vitamin supplements, which
can be supplementation within normal limits in
healthy people who get adequate vitamin D from
dietary sources and is a particular risk among peo-
ple who take megavitamins. The toxic level is fairly
low. Vitamin D toxicity is also a risk in people who
are receiving treatment for HYPOPARATHYROIDISM.
Excessive levels of vitamin D affect calcium reab-
sorption in the kidney (HYPERCALCEMIA) and often
cause kidney stones (NEPHROLITHIASIS) that can
result in permanent damage to the KIDNEYS.
Vitamin E (Tocopherol)A fat-soluble vitamin, vitamin E’s most important
function is as an antioxidant. It blocks the reaction
of free radicals to produce more free radicals and
some metabolism of fatty acids. Vitamin E also
maintains the integrity of erythrocytes (red blood
cells), which are vulnerable to damage, in the
blood circulation. Though vitamin E has a reputa-
tion for a wide range of actions in the body to pre-
vent diseases such as cancer andCARDIOVASCULAR
DISEASE(CVD); to treat conditions such as FIBROCYS-
TIC BREAST DISEASE; and to enhance physical
ENDURANCE, LIBIDO, and reproduction, research has
thus far failed to support these claims. Some
research suggests that excessive amounts of vita-
min E may in fact contribute to the development
of certain cancers. Much research remains under
way to better understand the roles of vitamin E in
health and in disease.
Vitamin E deficiency may occur in disorders of
fat absorption or metabolism though is quite rare.
When present vitamin E deficiency may result in
hemolytic anemia. Vitamin E toxicity is also
uncommon and nearly always occurs in people
who take excessive amounts of vitamin E supple-
ments. Vitamin E toxicity can have deleterious
effects on the mechanisms of COAGULATION, leading
to hemorrhage.Vitamin K (Quinone)
BACTERIAin the SMALL INTESTINEsynthesize 80 per-
cent or more of the VITAMINK the body needs and
uses. The other 20 percent comes from plant-based
foods, notably spinach, broccoli, and other dark
green vegetables. The bacterial form of vitamin K is
menaquinone; the plant form of vitamin K is phyl-
loquinone. Vitamin K is essential for the activation
of several CLOTTING FACTORS(VII, IC, X) and pro-
thrombin, which regulate the blood’s ability to clot.
Vitamin K deficiency may occur in disorders
that interfere with the absorption of fats into the
body, such as GALLBLADDER DISEASEand gastroin-
testinal malabsorption disorders. Long-term
antibiotic therapy can significantly reduce the bac-
teria count in the small intestine, restricting the
body’s ability to synthesize vitamin K. Anticoagu-
lant medications such as warfarin work by block-
ing the action of vitamin K. Untreated vitamin K
deficiency can result in life-threatening hemor-
rhage. Vitamin K toxicity is rare and occurs nearly
always when taking vitamin K supplements. It can
cause JAUNDICE and, when severe, permanent
BRAIN damage. Some multivitamin supplementsvitamins and health 207