So those combination vitamin D, and K products are scams?

Not at all. Suboptimal, but far better than taking nothing at all.

There are loads of nutrients that technically compete for absorption, but generally it isn’t a concern unless you are taking a huge dose of one. Even then, it’s not like little dog is completely blocked. I’d have to look at the studies the above comment is referencing to determine how much of a concern it actually would be.

Even if taking both together was 30% less effective than taking them apart, in the context that getting people to take a single pill daily with regard to timing is hard enough, it’s still a overall win. That said, I would agree such a situation should be reflected on the label.

“Less effective” is odd here because other commenters are saying that K2 ensures D gets deposited in the right places rather than build up in the arteries (as plaques presumably). So if it is, say 30% less effective, then taking them apart wouldn’t that mean that rather than getting (example) 1,000 IU in the wrong place, you’d get 700 IU deposited in the right place, so it would be more effective rather than less?

Every packaging label I’ve ever seen clearly claims how many IUs there are.

Let’s say it is 30%, there’s no way potential buyers, when they see ‘1000 IUs Vitamin D’ for example, will realize it actually means ‘700 IUs’.

So I don’t see how your comment makes sense.

The whole idea is that some research suggests that vitamin D may be harmful without vitamin K to offset its effects ("so that calcium doesn't build up in the vessels but goes to the bones where it's supposed to be"). That's all there is to it.

No need to discuss absorption. Furthermore, the idea "taking D and K at the exact same time reduces the absorption of D" is unsubstantiated in medical research

700 instead of 1000 would be “sub optimal” but better than 0. At least that’s what I think the above poster was trying to say.

K2, to be precise. K is involved in blood clotting; K2 isn’t.