Vitamin K is a fat-soluble vitamin, so it is stored in the body's fat tissue and liver. It is best known for its role in helping blood clot (coagulate) properly (the "K" comes from its German name, Koagulationsvitamin). Vitamin K also plays an important role in bone health.
It is rare to have a vitamin K deficiency, because in addition to being found in leafy green foods, the bacteria that are found in the intestines can make vitamin K. Sometimes taking antibiotics can kill the bacteria and lead to a mild deficiency. Vitamin K deficiency can lead to excessive bleeding (hemorrhage), which may begin as oozing from the gums or nose. Other circumstances that may lead to vitamin K deficiency include:
Health problems that can prevent the absorption of vitamin K (such as gallbladder or biliary disease, which may alter the absorption of fat), cystic fibrosis, celiac disease, and Crohn's disease
Use of blood-thinning medications (such as warfarin)
Other conditions that benefit from vitamin K include:
Vitamin K is used to reduce the risk of bleeding in liver disease, malabsorption syndromes, or in association with long-term use of antibiotics.
In the U.S., Canada, Great Britain, and many other countries, all newborns receive vitamin K injections to prevent the possibility of hemorrhage (particularly in the brain) just after delivery. Babies are born without any bacteria in their intestines and do not get enough vitamin K from breast milk to tide them over until their bodies are able to make it. (However, if a mother eats lots of green vegetables on a daily basis, she can improve the amount of vitamin K in breast milk.) Even though vitamin K deficiency in newborns is very rare, it is dangerous enough to warrant these measures. Newborns at greatest risk for vitamin K deficiency are those who are born prematurely or whose mother had to take seizure medications during the pregnancy. Mothers on seizure medications are often given oral vitamin K for 2 weeks prior to delivery.
Vitamin K is needed for proper use of calcium in bones. Higher vitamin K levels correspond to greater bone density, while low levels of vitamin K have been found in those with osteoporosis. There is increasing evidence that vitamin K improves bone health and reduces risk of bone fractures, particularly in postmenopausal women who are at risk for osteoporosis. In addition, studies of other groups (such as male and female athletes) have also shown bone enhancing benefits from vitamin K supplements.
Foods that contain a significant amount of vitamin K include beef liver, green tea, turnip greens, broccoli, kale, spinach, cabbage, asparagus, and dark green lettuce. Chlorophyll is the substance in plants that gives them their green color and provides vitamin K.
Freezing foods may destroy vitamin K, but heating does not affect it.
There are 3 forms of vitamin K:
Vitamin K1 (phylloquinone, the natural version of K1 and phytonadione, the synthetic type of K1)
Vitamin K2 (menaquinone)
Vitamin K3 (menaphthone or menadione)
K1 and K3 are both available as part of multivitamin complexes or alone, in 5 mg tablets. These fat-soluble forms are an excellent source of vitamin K.
Water-soluble chlorophyll is the most common form of vitamin K found over the counter. It is available in tablet, capsule, and liquid forms.
How to Take It:
As with all supplements, check with a health care provider before taking vitamin K or giving it to a child.
People with vitamin K deficiencies related to malabsorption (such as gallbladder or biliary disease, cystic fibrosis, celiac disease, and Crohn's disease) will benefit most from a multivitamin containing vitamin K, rather than an individual vitamin K supplement. In certain circumstances, your doctor may administer vitamin K by injection.
Daily intake for dietary vitamin K (according to the U.S. RDA) are listed below:
Infants birth to 6 months: 2 mcg
Infants 7 - 12 months: 2.5 mcg
Children 1 - 3 years: 30 mcg
Children 4 - 8 years: 55 mcg
Children 9 - 13 years: 60 mcg
Adolescents 14 - 18 years: 75 mcg
A single injection of vitamin K is also given at birth.
Males 19 years and older: 120 mcg
Females 19 years and older: 90 mcg
Pregnant and breast-feeding females 14 - 18 years: 75 mcg
Pregnant and breast-feeding females 19 years and older: 90 mcg
Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.
At recommended doses, vitamin K has few side effects.
Vitamin K crosses the placenta and is also excreted in breast milk. Therefore, pregnant women and women who are breastfeeding should talk to their doctor before taking vitamin K supplements.
People with an rare metabolic condition called Glucose-6-phosphate dehydrogenase (G6PD) deficiency should avoid vitamin K.
If you are currently being treated with any of the following medications, you should not take vitamin K without first talking to your health care provider.
Antibiotics -- Antibiotics, particularly a class known as cephalosporins, reduce the absorption of vitamin K in the body. Long-term use (more than 10 days) of antibiotics may result in vitamin K deficiency because these drugs kill not only harmful bacteria but also beneficial, vitamin K-activating bacteria. This is mot likely to occur in people who already have low levels of vitamin K or are at risk for deficiency (such as those who are malnourished, elderly, or taking warfarin). Cephalosporins include:
Phenytoin (Dilantin) -- Phenytoin interferes with the body's ability to use vitamin K. Taking anticonvulsants (such as phenytoin) during pregnancy or while breastfeeding may deplete vitamin K in newborns.
Warfarin (Coumadin) -- Vitamin K reduces the effects of the blood-thinning medication warfarin, rendering the medication ineffective. Vitamin K should not be taken while taking warfarin, and foods containing high amounts of vitamin K should be avoided.
Orlistat (Xenical, alli) and Olestra -- Orlistat, a medication used for weight loss, and olestra, a substance added to certain food products, prevent the absorption of fat and can reduce the body's absorption of fat-soluble vitamins. The Food and Drug Administration now requires that vitamin K and other fat-soluble vitamins (A, D, and E) be added to food products containing olestra. In addition, physicians who prescribe orlistat add a multivitamin with fat soluble vitamins to the regimen.
The fact that vitamin K is now added to olestra-containing foods is important to know if you should not be taking vitamin K (if you are on the blood thinner warfarin, for example).
Bile acid sequestrants -- These medications, used to reduce cholesterol, reduce the overall absorption of dietary fats and may also reduce absorption of fat-soluble vitamins. If you take one of these drugs, your doctor may recommend a vitamin K supplement:
Menadione; Menaphthone; Menaquinone; Phylloquinone
Reviewed last on: 9/7/2007
Steven D. Ehrlich, N.M.D., private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.
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