I take 5,000 IU of Vitamin D daily and 3 mg of Melatonin about an hour or so before bed. It has all but cured a lifetime of serious sleep issues.
If I take it when traveling, jet lag is greatly diminished and overcome much more rapidly. I switch to taking it 9 a.m. of the destination's local time. If 9 a.m. occurs during the flight, I take it then.
It's like an external clock pulse!
The first time I took 5000 D3, I made the mistake of doing it in the evening. My sleep that very night was quite strange, disturbed with weird dreams. I immediately clued in to the fact that morning might be better. Basically, mimicking the onset of daylight.
D3 is beneficial for exercise; it relieves that muscle soreness and tiredness and improves mental alertness. It helps beat those winter blues and gets you out there.
http://ctheblog.cforyourself.com/2008/12/overdosing-on-vitam...
When I get those teeth sensations, I back off the D3.
That blogger's experience with waking up early in the morning between 5-6 exactly matches mine, also.