Vitamin K is a group of fat soluble vitamins: K1, K2, and K3. K3 is synthetic and I personally advise against the use of synthetic vitamins whenever possible.
K1 and K2: K1 (phylloquinone) is made by plants, so it is only available through plant sources like grass, nettles, kale, etc and is converted to K2 through a cow’s (and various other animals) stomachs, and then more bioavailable and absorbable form for us humans. We have a limit on the amount of K1 we can use and absorb, since we are not equipped with the same digestive systems as those animals so while it IS useful for our mineral content and a good form to use for clotting factor, at a certain point that levels off, and it may help support the body and the teeth/bones, but the different forms of K have different biochemical pathways, so you cannot expect them to have the same functions. Neither should not be ignored or minimized, they are both essential.
K2 (menaquinone) has 2 forms, MK4 and MK7. MK4 is produced by animals from K1, so you can find it in the highest levels in dairy products of grass fed cows (particularly the “summer milk”) and also things like goose liver in the highest concentrations. Other animal livers and good quality egg yolks also have K2. MK7 is synthesized by bacteria, found primarily in natto (fermented soybeans) which is available, though perhaps not everywhere, and the ingredients should be monitored since often preservatives and other unwanted ingredients can be found in packaged natto.
It is somewhat unclear at this point whether MK7 is a satisfactory substitute for MK4.
These are essential nutrients, however, they do not complete their work as effectively in the absence of the appropriate ratio of naturally occurring Vitamins A and D, which is somewhere between 4 and 8 but hard to pinpoint exactly. It’s also hard to know exactly what amounts of A and D are in each batch of cod liver oil, for a variety of reasons, but we do know that the naturally occurring vitamins therein are in the proper ratio and do not cause toxicity.