Vitamins: Need them or not?

I recently started taking Vitamin D3 per my doctor's recommendation. He said that, particularly, with the onset of fall and winter and less exposure to natural sunlight for this vitamin D, it's important. I take a gel capsule in the evening and sleep beautifully and wake very refreshed and rested. It's also very important for bone and muscle regeneration.

I try to take a multivitamin regularly, and I notice that I tend to be sick less when I'm taking them. Along with exercise, they help to keep my energy level and immunity high.