Encyclopedia of Health and Medicine

V
vitamin K A vitamin that is a crucial catalyst, or
coenzyme, in the COAGULATION process (also called
coagulation cascade). Vitamin K (naphthoquinone)
plays a role in activating seven of the
CLOTTING FACTORS in various stages of coagulation,
helping convert them from the inactive state in
which they circulate in the BLOOD to active proteins
that form clots. Vitamin K also is important
for new BONE growth and BONE DENSITY. The major
forms of vitamin K are phylloquinone (K1),
menaquinone (K2), and menadione (K3, synthetic
and cannot be converted into K1).
DIETARY SOURCES OF VITAMIN K
Food
Amount of Vitamin K
per 1-Cup Serving
Kale, cooked
1,062 micrograms (mcg)
spinach, cooked
888 mcg
collard greens
836 mcg
parsley
324 mcg
Brussels sprouts, cooked 219 mcg
onions, spring
207 mcg
broccoli, cooked
220 mcg
lettuce, leaf (Bibb, Boston) 167 mcg
asparagus, cooked
144 mcg
prunes, stewed
65 mcg
lettuce, romaine
57 mcg
peas, cooked
40 mcg
blackberries, blueberries (fresh) 28 mcg
lettuce, head (iceberg) 13 mcg
turkey, cooked
5 mcg
strawberries, raw
4 mcg
Source: USDA National Nutrient Database for Standard Reference,
SR17 Nutrients List: Vitamin K (Phylloquinone)
Most of the vitamin K the body uses is in the
form of phylloquinone and comes from plant
foods in the diet, notably leafy green vegetables
such as spinach, kale, and broccoli. Intestinal BAC-
TERIA also synthesize (manufacture) a small
amount of vitamin K (menaquinone). Though
vitamin K is fat soluble, the body does not maintain
a significant store of it. Consequently, health
experts have established daily adequate intake
values of 90 micrograms per day for women and
120 micrograms per day for men.
The commonly used oral anticoagulant medication,
warfarin, inhibits clotting by blocking the
actions of vitamin K. Doctors may recommend
restricting consumption of foods high in vitamin K
for those who are taking ANTICOAGULATION THERAPY
or maintaining consistent consumption of vitamin
K–containing foods (not to exceed the daily adequate
intake value) so the body’s levels of vitamin
K remain stable.
Because infants often have inadequate levels of
vitamin K in their blood at birth, most hospitals in
the United States administer vitamin K supplement
injections to newborns within 24 hours of
birth, which is the current recommendation of the
American Academy of Pediatrics. Doctors do not
agree on the value or effectiveness of routine vitamin
K supplements in other circumstances. Most
health experts recommend obtaining the body’s
supply of vitamin K through dietary sources,
which is fairly easy for most Americans to do
because a wide variety of foods contain this nutrient.
Menadione is the synthetic supplement form
of vitamin K.
See also ANTICOAGULATION THERAPY; OSTEOPOROSIS;
VITAMINS AND HEALTH.
von Willebrand’s disease A hereditary, genetic
bleeding disorder resulting from a deficiency or
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