Vitamin A, D, E, K or all Fat soluble. Meaning it requires Fat to unlock its ability. It is more potent when taken with Fat.
Anything over 5,000 I.U. is the therapeutic dosages.
If you are already slightly overweight, it will help you burn away fat so you don't need to take it with FAT.
Try taking it at night and you will sleep better. You may feel warm though.