Vitamin K is a fat-soluble vitamin, so it is stored in fatty tissue in the body. Three types of compound have vitamin K activity: K1, K2 and K3. Most of our dietary intake is in the form of vitamin K1, from vegetables such as broccoli and cauliflower. However, we obtain only very small amounts of the most useful form, vitamin K2, which is found, for example in probiotic foods.
Some vitamin K2 is made naturally by probiotic bacteria in the bowel. Absorption is not that efficient, however, and the amounts made are not enough to need our needs. Production appears to be reduced in older people and in those taking antibiotics.
Good sources of vitamin K1 include green leafy vegetables such as broccoli, cabbage, cauliflower, spinach, and vegetable oils and cereals. Fermented foods like sauerkraut, cheese and other probiotic foods are good sources of vitamin K2.
To obtain the heart and circulatory benefits of this vitamin, look for supplements that contain vitamin K2 rather than vitamin K1 where possible, but not vitamin K3, or menadione, which is a synthetic, man-made form of the vitamin.
 Cockayne S, et al. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med 2006; 166(12):1256-61.
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