[beagle3]

There's a difference between sickness-causing deficiency and optimal level. Most people are somewhere in between. If you tried and it didn't make a difference, then you're probably around the optimal level.

However, the specifics do matter; see e.g. https://www.gwern.net/zeo/Vitamin-D - this is n=1 but consistent with many other n=1 self-experiments I'm familiar with; personally, my sleep is improved with increased protein consumption AND 10,000 IU D3 before 10AM (Both contribute; I've not gone about 10,000 IU, but 5,000 UI has a much lesser effect)

I have not find a peer reviewed time-of-taking-D3 paper when I looked, but D3 is recognized as a timing mechanism ("Zeitgebber") in many papers I've found.