I originally put it in, along with vitamin c during flu season, but felt I haven't personally done enough research to make claims about them. Regarding vitamin d, I am unsure about whether it should be taken with vitamin k or not.
With K2 to counteract the risk of soft tissue calcification.
It’s a common deficiency especially in the winter, but most people don’t benefit from regular supplements.
At least assuming 20ng/mL is a reasonable minimum. Some people suggest that’s a little low, but there’s real issues with excess vitamin D.