Vitamin K1 and K2 — two vitamins sharing a name, doing completely different jobs
K1 handles blood clotting. K2 handles where calcium goes in the body. They are metabolically separate.
nutrition
Vitamin K1 is abundant in green leafy vegetables — kale, spinach, parsley, dill. It activates clotting factors in the liver. Most standard nutrition databases report total Vitamin K, which for plant foods is almost entirely K1.
Vitamin K2 activates two with entirely different functions: osteocalcin, which binds into bone matrix, and Matrix Gla which actively prevents from depositing in arterial walls. Arterial calcification — a major driver of cardiovascular disease — may be partly a K2 deficiency problem, not purely a problem. The Rotterdam Study found high K2 intake associated with dramatically lower cardiovascular mortality.
K2 exists in several forms. MK-4 is found in grass-fed animal products — butter, egg yolk, liver. MK-7 is produced by bacterial fermentation and is the most bioavailable and longest-acting form. Natto (fermented soybeans) contains extraordinary concentrations of MK-7 — a single serving can exceed the adequate intake by 10x. Aged hard cheeses (Gouda, Brie, Edam) are the most accessible Western source of K2.
K1 sources: kale, spinach, parsley, dill, broccoli, Brussels sprouts
MK-4 sources: grass-fed butter, ghee, egg yolk, chicken liver — negligible from grain-fed animals
MK-7 sources: natto (by far the richest), aged hard cheese, some fermented vegetables
Sauerkraut contains MK-7 at roughly 2–7g per 100g — meaningful but modest compared to natto