06/04/2026
THE FORM THAT CROSSES. 🧠💊
You stand in the supplement aisle and the bottle just says "magnesium 400 mg." It looks like the responsible choice. It almost certainly isn't. The vast majority of cheap bottles use magnesium oxide because it's the cheapest source. Magnesium oxide has a bioavailability of about 4 percent, which means 384 of those 400 mg never enter your bloodstream. They reach your colon and pull water in, which is why the "magnesium for sleep" people keep ending up in the bathroom instead of asleep.
Magnesium glycinate, bound to the amino acid glycine, absorbs at around 40 percent and reaches muscle and nerve tissue. That's the one for cramps, anxiety and sleep onset. Magnesium citrate sits in the middle at 30 percent absorption and is fine for general repletion. But neither of those crosses into the brain.
Magnesium L-threonate is the only form that meaningfully crosses the blood-brain barrier and raises magnesium concentration in cerebrospinal fluid. A 2010 study by Slutsky and colleagues at MIT and Tsinghua, published in Neuron, showed that this specific form increased synaptic density and improved working memory in animal models. Follow-up human work has shown improvements in cognitive scores in older adults with mild memory complaints.
It costs more. It's almost never on the front of a multivitamin. And it's the only one that does what most people are actually buying magnesium for — sharper thinking and deeper sleep.
Which form is in the bottle you take? 👇
📚 Study: Slutsky I et al., 2010 — Enhancement of learning and memory by elevating brain magnesium (Neuron, PMID 20152124)
