It is really amazing what a difference a bit of Vitamin D can do! Like pretty much everyone else who lives in the Seattle area, I'm really deficient. Awhile back, we ran out of D and I hadn't had a chance to go pick a refill but I figured, really, how bit a difference can it make? Within just a few days I was literally dragging... couldn't figure out what was wrong and was really worried I was coming down with something, until a lightbulb finally went off. Got a refill on my D, started taking it again and within a few days was amazed at the amount of energy I had.