A good place to get affordable vitamins, although not all the ones you need is swansonvitamins.com. A good friend of mine told me about this site and now I recommend it to others. It is where I get many of my supplements. They don't have everything I need or in all the doses that I need, but they have enough to where it's worth paying the shipping costs when I order several items at once. I know that they have many in powdered and liquid forms, although not all of them. Still, many of the items are half the price or less than what the quality discount vitamin store sells theirs for. I have had good results with the supplements that I do take from that place. They must be doing something if my blood tests show improvements.
To answer the initial question, I remember reading some time ago that Magnesium Oxide is the *least* bioavailable of all the possibilities, but also the cheapest to make, which is why it's so often used. I seem to remember the others being about the same, give or take, so Magnesium Citrate is probably as good as anything else and better than the Oxide.
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