Vitamin K
A fat-soluble vitamin essential for blood clotting (K1) and for keeping calcium in the bones rather than the arteries (K2), in two complementary forms.
Vitamin K exists in two main forms with distinct roles:
- K1 (phylloquinone): plant-derived (green vegetables), involved mainly in blood clotting
- K2 (menaquinone): of bacterial/animal origin and found in fermented foods, involved mainly in fixing calcium in the bones
The original angle (K2, the conductor of calcium): vitamin K2 is the forgotten nutrient of bone and cardiovascular health. Its role: to activate proteins (osteocalcin, MGP) that direct calcium towards the bones and away from the arteries.
The major consequence: without enough K2, calcium (even if well absorbed thanks to vitamin D) can be deposited in the arteries (calcification, stiffness, cardiovascular risk) instead of strengthening the bones. This is the “calcium paradox”: too much poorly directed calcium harms the arteries without benefiting the bones.
Hence the crucial D + K2 synergy: vitamin D makes you absorb calcium, K2 puts it in the right place. Taking high-dose vitamin D WITHOUT K2 could be counter-productive (calcium absorbed but poorly directed).
The fascinating Japanese source: the most potent K2 (MK-7) is abundant in natto (Japanese fermented soya). Regions of Japan that eat a lot of natto have better bone and cardiovascular markers, a link that has been studied.
⚠️ Drug interaction: vitamin K interacts with vitamin K antagonist anticoagulants (warfarin, Previscan). Patients on these treatments must keep their vitamin K intake stable (neither cutting out green vegetables nor suddenly overeating them). Medical advice always comes first.
Sources: K1 in green vegetables (kale, spinach, broccoli, parsley); K2 in natto (the champion), fermented cheeses, egg yolk, liver, and products from grass-fed animals.