It’s not new knowledge, but it is still one of the more frequent mistakes I see done: taking vitamin D mixed with other minerals such as with calcium.
Fact is, when you mix vitamin D with minerals it gets degraded rapidly - which is why you should always take vitamin D isolated in its own supplement, if you want to actually absorb what you are taking.
Read the study here: https://jamanetwork.com/journals/jama/article-abstract/326928