Vitamin K is best known for its role in helping blood clot properly, and in preventing excessive bleeding. It also plays an important role in bone health.

Vitamin K protects the body against the following:

• Bleeding. Vitamin K is used to reduce risk of bleeding in liver disease, jaundice, malabsorption, or in association with long-term use of aspirin or antibiotics. Vitamin K has been used in the treatment of heavy menstrual bleeding, and with vitamin C to treat morning sickness. Babies are sometimes given a vitamin K injection soon after birth, because in certain cases, such as in premature infants, they are at increased risk for bleeding.
• Osteoporosis. Vitamin K is needed for bones to use calcium. Vitamin K supplements may improve bone mass in postmenopausal women. Vitamin K deficiency is linked to osteoporosis because low levels have been found in those with the condition. Supplements of vitamin K have been used to treat osteoporosis.

Vitamin K also helps in the following ways:

• Vitamin K may prevent kidney stones.
• A vitamin K analog, K compound 5, may stop liver cancer growth.
• Some forms (water-soluble chlorophyll) help control body, fecal, and urinary odor.
• Water-soluble forms are used to treat skin wounds.

In addition, preliminary evidence suggests that vitamin K₃, the synthetic form of vitamin K, may inhibit the growth of some bone marrow cells, specifically, chronic myelogenous leukemia (CML) cells, and enhance the chemotherapeutic effects of doxorubicin. However, these results have not yet been demonstrated in humans; further clinical studies may be warranted.

Foods that contain a significant amount of vitamin K include chlorophyll, green tea, turnip greens, broccoli, spinach, cabbage, asparagus, and dark green lettuce.

Freezing foods may destroy vitamin K, but heating does not affect it.

• Vitamin K supplements are available in both natural and synthetic forms.
• Supplements of fat-soluble chlorophyll are an excellent source of vitamin K.
• Water-soluble chlorophyll is the most common form of vitamin K found over the counter. The water-soluble form is not absorbed into the body, and is useful for treatment of skin, and to reduce body odor.
• Vitamin K is available in multivitamin complexes, and as 5-mg tablets.

As with all supplements, check with a healthcare provider before giving vitamin K to a child.

Daily intake for dietary vitamin K (according to the U.S. RDA) are listed below:

Pediatric

• Infants birth to 6 months: 2 mcg
• Infants 7 to 12 months: 2.5 mcg
• Children 1 to 3 years: 30 mcg
• Children 4 to 8 years: 55 mcg
• Children 9 to 13 years: 60 mcg
• Adolescents 14 to 18 years: 75 mcg

To prevent neonatal hemorrhage: a healthcare provider administers three 1 to 2 mg doses, the first given at the first feeding, the second at 2 to 4 weeks, and the third at 8 weeks.

Adult

• Males 19 years and older: 120 mcg
• Females 19 years and older: 90 mcg
• Pregnant and breastfeeding females 14 to 18 years: 75 mcg
• Pregnant and breastfeeding females 19 years and older: 90 mcg

• Vitamin K can interfere with the action of anticoagulants such as warfarin.
• X-rays and radiation can raise vitamin K requirements.
• Vitamin K is excreted in breast milk, and crosses the placenta. Pregnant women and women who are breast-feeding should consult their health care provider before starting vitamin K supplements.
• Your body may need more vitamin K if you are taking aspirin, cholestyramine, phenytoin, or mineral oil laxatives.
• Some snake venoms destroy vitamin K, which helps blood clot properly. Vitamin K may be injected to stop the bleeding from snakebite.
• Extended use of antibiotics may result in vitamin K deficiency. These drugs kill not only harmful bacteria, but also beneficial, vitamin K-activating bacteria.

Vitamin K reduces the effects of the blood-thinning medication warfarin, rendering the medication ineffective. When taking this medication, do not take vitamin K supplements and avoid foods with high quantities of this nutrient unless instructed to do otherwise by your healthcare provider.

Antibiotics, particularly a class known as cephalosporins, reduce the absorption of vitamin K. This is particularly a problem for 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).

The cholesterol-lowering medication cholestyramine may also reduce the absorption of vitamin K.

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; consult your obstetrician and/or pediatrician for advice on nutrient replacement therapy.

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