Question to HN: To what extent do we understand vitamin D's activity in our body? A lot of the focus seems to be on the bone, muscle, teeth, etc. components, b

Question to HN: To what extent do we understand vitamin D's activity in our body? A lot of the focus seems to be on the bone, muscle, teeth, etc. components, but I also hear often about headlines like in the OP or its significance in improving mood. I would like to know if there's potential that we know little about its complete set of effects.