I did quite a bit of research on magnesium deficiency. A lot of evidence points to mag def in those with malabsorption, bad diet, etc.. It can cause a whole host of problems if it is low. Knowing which brand is most absorbable is hard b/c they all claim to be good. I did read that mag oxide is not a good choice. That is what we are currently giving our daughter. I will continue to read and see what I can find. In the meantime, we are having her mag and zinc levels checked. Will be interesting.