Been taking 10k IU of D3 for a few months now, managed to get my measurement from the teens or 20s into the 90s of whatever unit that's in. I believe 100 is the max of the healthy range. Can't tell the difference, but allegedly you're going to feel "worse" if you're low on this stuff.

It would be amusing to find out that it actually makes no difference at all and it's all placebo.