Vitamin K1 is found chiefly in leafy green vegetables such as spinach, swiss chard, and ''Brassica'' (''e.g.'' cabbage, kale, cauliflower, broccoli, and brussels sprouts); some fruits such as avocado and kiwifruit are also high in Vitamin K. By way of reference, two tablespoons of parsley contain 153% of the recommended daily amount of vitamin K.. Some vegetable oils, notably soybean, contain vitamin K, but at levels that would require relatively large caloric consumption to meet the USDA recommended levels.
It is believed that phylloquinone's tight binding to the thylakoid membranes in the chloroplasts is the reason behind the poor bioavailability of vitamin K in green plants. For example, cooked spinach has a 4 percent bioavailability of phylloquinone. However when one adds butter to the spinach, the bioavailability increases to 13 percent due to the increased solubility of vitamin K in fat.
Menaquinone-4 and Menaquinone-7 (vitamin K2) are found in meat, eggs, dairy, and natto. MK-4 is synthesized by animal tissues, the rest (mainly MK-7) are synthesized by bacteria during fermentation. In natto 0% of vitamin K is from MK-4 and in cheese 2–7%.
Gut bacteria produce significant amounts of usable vitamin K. In Haemorrhagic disease of the newborn, the gut has not yet been colonized with bacteria, and to prevent this disease, vitamin K shots are given to babies born in the US. Similarly, persons on large doses of antibiotics are at risk for developing vitamin K deficiency because of a lack of normal flora.
Further Reading
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