Magnesium Supplements May Not Deliver to the Brain, Despite Label Claims

Cheap magnesium oxide pills largely fail to dissolve, acting instead as laxatives that draw water into the intestines. The body holds roughly 25 grams of magnesium, over half stored in bone, with the remainder distributed across cells and involved in hundreds of reactions, from DNA and protein synthesis to nervous-system signaling. In supplement form the element arrives as a magnesium salt that must dissolve to release Mg²⁺, and absorption depends on dose, stomach contents and existing magnesium levels — the higher the dose, the lower the proportion absorbed. Magnesium citrate has shown the highest bioavailability in laboratory tests, yet all salts still break down in the intestine. Some labels nonetheless claim blends target magnesium to muscles or the brain, claims often built on rodent experiments that supplied the animals long-term at doses above those in a pill. One rat study found magnesium L-threonate raised brain magnesium and improved some learning and memory measures, the basis for marketing asserting the salt reaches the brain directly. Small randomized human trials reporting cognitive or sleep improvements carry caveats: some tested mixtures, ran only weeks, analyzed few outcomes, or were funded by manufacturers or run by their staff. None measured brain magnesium content. The story originally appeared on WIRED Czech Republic and Slovakia, translated from Czech.