How Much Vitamin K Should One Take?

You may have been told to "eat your greens" and for good reason. Vitamin K is a fat-soluble vitamin that's crucial in the blood clotting process. The primary dietary source is green vegetables. There are three forms of vitamin K. Vitamin K-1, phylloquinone is made by plants, while vitamin K-2, menaquinone is produced by bacteria in your intestine. Vitamin K-3, menadione is the synthetic form, used in multivitamins.

Vitamin K Functions

The main function of vitamin K is blood coagulation. Vitamin K helps to make some of the proteins required for blood clotting, including prothrombin. Newborn babies are given a vitamin K injection at birth to reduce the risk of hemorrhage. Vitamin K plays a role in healthy bone function. A study published in the February 2003 "The American Journal of Clinical Nutrition" found women who had an inadequate intake of dietary vitamin K-1, phylloquinone, had low bone mineral density and were at an increased risk of suffering a fractured hip.

Recommended Daily Intake

The daily, dietary reference intake for vitamin K varies, depending on your age and sex. It's set by the Food and Nutrition Board of the Institute of Medicine. The DRI for infants 0 to 6 months is 2 mcg and for infants between 7 and 12 months it's 2.5 mcg. The DRI for children 1 to 3 years is 30 mcg; for 4 to 8 years it's 55 mcg and for 9 to 13 years it's 60 mcg. For teens aged 14 to 18 years, it's 75 mcg. For men 19 years and above it's 120 mcg, for women 19 years and above it's 90 mcg.

Sources

Plants produce phylloquinone, so green vegetables like spinach, collards, brussels sprouts, kale and broccoli are excellent sources of vitamin K. A cup of boiled spinach contains 888.5 mcg of vitamin K. Cereals and vegetable oils, like soybean oil, olive oil and canola oil, are also good sources of vitamin K.

Considerations

Although vitamin K deficiency is uncommon, you're at a greater risk under certain circumstances. Vitamin K is a fat-soluble vitamin; diseases that interfere with fat absorption can lead to a deficiency, such as celiac disease, cystic fibrosis, Crohn's disease and cholestasis. Taking antibiotics over a prolonged period destroys the vitamin K-producing bacteria in your intestines, resulting in a mild deficiency. Anticoagulant drugs such as warfarin, sold under the brand name Coumadin, interfere with vitamin K activity and liver disease can also lead to a deficiency.