Do you need vitamin K2 with vitamin D?
You do not need vitamin K2 just because you take vitamin D. The randomized AVADEC trial gave vitamin K2 and vitamin D to people with aortic valve calcification and did not show slower valve disease. Vitamin D still has a dietary allowance of its own. K2 has a separate, thinner evidence file. Buy the combination only if you have a reason for both, not because a label says they belong together.
The combination bottle is one of the most common add-ons sold next to vitamin D3. Vitamin K2 (MK-7) is a real compound with its own research. It is not a required partner.
The valve trial
The AVADEC trial randomized people with aortic valve calcification to vitamin K2 plus vitamin D or to placebo (PMID 35465686, Circulation). The combination did not slow the valve disease the trial was built to measure. That is a direct answer to the claim that the pair protects arteries or valves in this setting. It is not a finding that vitamin D itself is useless for its actual jobs, which are nutritional.
When K is a drug interaction
Vitamin K interferes with warfarin. A K2 softgel is not a casual add for anyone on that drug. For everyone else, a vitamin D product in the 600 to 2,000 IU range does not become incomplete because K2 is missing. See vitamin D in a Canadian winter for the allowance and the upper limit.