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Vitamin K

Also indexed as:K Vitamin, Phylloquinone (Vitamin K), Phytonadione (Vitamin K), Vitamin K1, K1
Vitamin K: Main Image

How to Use It

The recommended dietary allowance for vitamin K is about 1 mcg per 2.2 pounds of body weight per day or about 65 to 80 mcg per day for most adults.34 This level of intake may be achieved by consuming adequate amounts of leafy green vegetables. However, studies have shown that many men and women aged 18 to 44 years ingest less than the recommended amount of vitamin K.35, 36

Where to Find It

Leafy green vegetables, such as spinach, kale, collards, and broccoli, are the best sources of vitamin K. The greener the plant, the higher the vitamin K content.37 Other significant dietary sources of vitamin K include soybean oil, olive oil, cottonseed oil, and canola oil.38

Possible Deficiencies

A vitamin K deficiency, which causes uncontrolled bleeding, is rare, except in people with certain malabsorption diseases. However, there are reports of severe vitamin K deficiency developing in hospitalized patients who had poor food intake and were receiving antibiotics.39 All newborn infants receive vitamin K to prevent deficiencies that sometimes develop in breast-fed infants.

Best Form to Take

Vitamin K comprises a group of structurally related compounds, including vitamin K1 (the major form found in plants), vitamin K2 (including menaquinone-4 [MK-4], also known as menatetrenone; and menaquinone-7 [MK-7]), and vitamin K3. Vitamin K supplements contain vitamin K1, MK-4, or MK-7. While there is some evidence indicating that MK-7 raises vitamin K blood levels the most, there is insufficient clinical research to indicate that this form of the vitamin is more effective than the other forms. MK-4 given in very large amounts has been used successfully in certain conditions but it is not clear whether the benefits are due to its vitamin K activity or to some other biological function.40

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The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2017.