If you're going to take one supplement, go for Magnesium Citrate. Take 200mg 3x daily (with or without food is ok). Almost every client I have ever seen is deficient in magnesium. Magnesium deficiency can trigger sugar cravings, irritability, trouble sleeping, headaches, tension, muscle cramps and kidney weakness. Also, your body needs magnesium in order to make Vitamin D. For the rest of your vitamins, you can get them from food, but magnesium in particular is difficult for the body to absorb.