Unfortunately I have not seen any study that has been conceived in such a way that could allow to determine whether supplements with vitamin K2 are useful or not.
It is known with certainty that humans convert a part of the ingested vitamin K1 into vitamin K2.
While there have been many studies that have shown beneficial effects of supplements with vitamin K2, none of them have used a correct control group.
A deficiency in vitamin K2 can have two causes, either the capacity of a human body to produce vitamin K2 is not enough to cover the necessary amount of it, or the daily intake of vitamin K1 has been too low.
In order to distinguish the two causes, the control group, which does not take vitamin K2 supplements, must have a much greater daily intake of vitamin K1, perhaps 10 times or 20 times greater.
It is possible that the relationship between vitamin K1 and vitamin K2 is like between beta carotene and vitamin A, where, with a high enough daily intake of beta carotene, vitamin A is no longer needed, because the body can produce enough of it.
Unlike for beta carotene, we do not know yet whether there is a threshold of daily intake of vitamin K1 above which there is no need of vitamin K2 supplements.
It would be important to know this for sure, because vitamin K1 is extremely abundant in many green vegetables and it would be simple to reach very high daily intakes without any nutritional supplements.
It is known with certainty that humans convert a part of the ingested vitamin K1 into vitamin K2.
While there have been many studies that have shown beneficial effects of supplements with vitamin K2, none of them have used a correct control group.
A deficiency in vitamin K2 can have two causes, either the capacity of a human body to produce vitamin K2 is not enough to cover the necessary amount of it, or the daily intake of vitamin K1 has been too low.
In order to distinguish the two causes, the control group, which does not take vitamin K2 supplements, must have a much greater daily intake of vitamin K1, perhaps 10 times or 20 times greater.
It is possible that the relationship between vitamin K1 and vitamin K2 is like between beta carotene and vitamin A, where, with a high enough daily intake of beta carotene, vitamin A is no longer needed, because the body can produce enough of it.
Unlike for beta carotene, we do not know yet whether there is a threshold of daily intake of vitamin K1 above which there is no need of vitamin K2 supplements.
It would be important to know this for sure, because vitamin K1 is extremely abundant in many green vegetables and it would be simple to reach very high daily intakes without any nutritional supplements.