The two sources of vitamin K are plants and bacteria. Vitamin K1 (phylloquinone) is made exclusively by plants, where it is found in the chloroplasts; Its function is that of electron carrier during CO2 fixation. Hence green plants are rich sources of vitamin K1. Menaquinones (K2 vitamins) are of bacterial origin, and they are notably produced by Bacillus subtilis natto, Lactobacillus lacti and some colonic bacteria.
Vitamin K1 Vitamin K2
At low concentrations vitamin K is found in a wide variety of food items, but nutritionally relevant amounts of K1 are only found in green vegetables and some plant oils, whereas rich sources of vitamin K2 are found in cheese, curd cheese and the Japanese food natto. (click here to see Table as PDF)
Since all K vitamins need bile salts for intestinal absorption, the contribution of vitamin K produced by the intestinal flora is limited: bile salts are absorbed in the small intestine, whereas the production of vitamin K2 takes place further downstream in the colon.
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