You can get something like 37% of the RDA for Magnesium from just a 1/4 cup of shelled pumpkin seeds. Then eat other food sources that contain magnesium, and you are way ahead of the game as compared to taking supplements. Food sources include whole grains, dark chocolate, black beans, (and other beans), milk, yoghurt, etc. Honestly, the healthiest thing you can do is to eat those healthy foods, and others. And don't bother with the supplement unless recommended by a doctor based on low levels or some other medical condition which would warrant it (as defined by your doc).