Vitamin K deficiency
Definition
Vitamin K deficiency exists when chronic failure to eat sufficient
amounts of vitamin K results in a tendency for spontaneous bleeding or in
prolonged and excessive bleeding with trauma or injury. Vitamin K deficiency
occurs also in newborn infants, as well as in people treated with certain
antibiotics. The protein in the body most affected by vitamin K deficiency is a
blood-clotting protein called prothrombin.
Description
Vitamin K is a fat-soluble vitamin. The recommended dietary allowance
(RDA) for vitamin K is 80 mg/day for the adult man, 65 mg/day for the adult
woman, and 5 mg/day for the newborn infant. The vitamin K present in plant foods
is called phylloquinone; while the form of the vitamin present in animal foods
is called menaquinone. Both of these vitamins are absorbed from the diet and
converted to an active form called dihydrovitamin K.
Spinach, lettuce, broccoli, brussels sprouts, and cabbage are good
sources of vitamin K, containing about 8 mg vitamin K/kg food. Cow milk is also
a good source of the vitamin.
A portion of the body's vitamin K is supplied by bacteria living in
the intestine rather than by dietary sources.
Vitamin K plays an important role in blood clotting. Without the
vitamin, even a small cut would cause continuous bleeding in the body, and
death. Blood clotting is a process that begins automatically when any injury
produces a tear in a blood vessel. The process of blood clotting involves a
collection of molecules, which circulate continuously through the bloodstream.
When an injury occurs, these molecules rapidly assemble and form the blood clot.
The clotting factors are proteins, and include proteins called Factor II, Factor
VII, Factor IX, and Factor X. Factor II is also called prothrombin. These
proteins require vitamin K for their synthesis in the body. The blood-clotting
process also requires a dozen other proteins that do not need vitamin K for
their synthesis.
Causes and
symptoms
Newborns are especially prone to vitamin K deficiency. A
nursing-mother's milk is low in the vitamin; breast milk can supply only about
20% of the infant's requirement. Infants are born with low levels of vitamin K
in their body; they do not have any vitamin K-producing bacteria in their
intestines. Their digestive tracts are sterile. As a result, a form of vitamin K
deficiency, called hemorrhagic disease of the newborn, may develop. This disease
involves spontaneous bleeding beneath the skin or elsewhere in the infant's
body, and occurs in about 1% of all infants. In rare cases, it causes death due
to spontaneous bleeding in the brain.
Vitamin K deficiency in adults is rare. When it occurs, it is found
in people with diseases that prevent the absorption of fat. These diseases
include cystic fibrosis, celiac disease, and cholestasis. Vitamin K deficiency
can exist in adults treated with antibiotics that kill the bacteria that
normally live in the digestive tract. As mentioned, the intestine-bacteria
supply part of our daily requirement of vitamin K. Vitamin K deficiency can
result in bleeding gums, and in skin that is easily bruised.
Diagnosis
Vitamin K status is measured by the prothrombin time test. The normal
prothrombin time is about 13 seconds. With vitamin K deficiency, the prothrombin
time can be several minutes. The test involves taking a sample of blood, placing
it in a machine called a fibrometer, and measuring the time it takes for
blood-clot formation. Blood-clotting problems can also be caused by a rare
genetic disease called hemophilia. Hemophilia is not related to vitamin K
deficiency. Once vitamin K deficiency is suspected, further tests must be used
to distinguish it from possible hemophilia. Where a bleeding disorder can be
corrected by vitamin K treatment, the diagnosis of vitamin K deficiency is
proven to be correct.
Treatment
Vitamin K deficiency in newborn infants is treated and prevented with
a single injection of phylloquinone (5 mg). Adults with vitamin K deficiency are
treated with daily oral doses of 10 mg phylloquinone for one week.
Prognosis
The prognosis for correcting vitamin K deficiency, and associated
blood-clotting problems, is excellent.
Prevention
Aside from newborns and young infants, vitamin K deficiency is not a
concern for the general population. Vitamin K deficiency can be prevented by
assuring that the diet contains foods such as spinach, cabbage, brussels
sprouts, and eggs. Soybean oil, canola oil, and olive oil are good sources of
the vitamin, while corn oil and peanut oil are very poor sources.
Key Terms
Fat-soluble vitamin
Fat-soluble vitamins can be dissolved
in oil or in melted fat.
Hemorrhage
Bleeding that continues for an
abnormally long period of time.
Prothrombin
Prothrombin is a blood-clotting
protein. Injury to a blood vessel produces a signal which triggers the
conversion of prothrombin to thrombin. Thrombin is a protein which plays a
central role in provoking the assembly of other proteins to form the blood clot.
Recommended Dietary Allowance (RDA)
The Recommended Dietary Allowances
(RDAs) are quantities of nutrients in the diet that are required to maintain
good health in people. RDAs are established by the Food and Nutrition Board of
the National Academy of Sciences, and may be revised every few years. A separate
RDA value exists for each nutrient. The RDA values refer to the amount of
nutrient expected to maintain good health in people. The actual amounts of each
nutrient required to maintain good health in specific individuals differ from
person to person.
Water-soluble vitamins
Water-soluble vitamins can be
dissolved in water or juice.
