Hi everyone, I recently finished up a 40-day double-blind randomized placebo-controlled trial on whether/how Vitamin D affected my sleep (as measured by a Zeo); summary: vitamin D hurt my sleep when taken at night.
You can find the background & literature search, experiment setup, data (tabular & raw), and statistical analysis (in R) here: http://www.gwern.net/Zeo#vitamin-d
I figure there are so many people here using vitamin D that someone must be taking it at or near bedtime, and they really should hear about this.