That's really interesting, I've never seen a study showing oxide outperforming any other form, thanks for posting that. It doesn't really seem like a fair comparison, though, because they were using almost
twice the amount of elemental magnesium in the oxide form compared to the citrate form.
Even still, with how low the absorption rate of oxide has been shown elsewhere, that probably wouldn't be enough to completely count for the higher levels found in the oxide group, but it still seems a bit fishy to me. I don't have a science background, so maybe this a valid approach in comparing two different forms of something. I would expect that for a fair comparison they would use equivalent amounts of elemental magnesium with both groups.
From your link:
In a randomized, prospective, double-blind, crossover study, 41 (20 women) healthy volunteers [mean age 53±8 (range 31-75) years] received either
magnesium oxide monohydrate tablets (520 mg/day of elemental magnesium) or
magnesium citrate tablets (295.8 mg/day of elemental magnesium) for one month (phase 1), followed by a four-week wash-out period, and then crossover treatment for one month (phase 2).
EDIT: I'm not trying to argue about which form of magnesium is best. If you have a personal reason for using Mg oxide, say you've tested it in isolation and it works well for you, or it's the only form available to you, etc...then by all means keep using it. Having myself wasted tons of money on supplements, I'm just trying to point out that since many sources and studies agree oxide is an inferior poorly absorbed form, it might not be worth using.