There are over a dozen forms of magnesium sold as supplements. Only two — threonate and bisglycinate — have meaningful evidence for crossing the blood-brain barrier and improving sleep and cognitive function. Most people are taking the wrong one.
Magnesium is involved in over 300 enzymatic reactions in the body, and roughly 50% of the US population is deficient. But here's what most people miss: not all magnesium is the same, and the form determines where it goes. Magnesium oxide has poor bioavailability — most of it stays in the gut, which is why it's effective as a laxative but useless for your brain. Magnesium citrate is slightly better absorbed but still primarily acts in the periphery.
Magnesium L-threonate, developed at MIT by Dr. Guosong Liu, was specifically designed to cross the blood-brain barrier. Slutsky et al. published in Neuron that magnesium threonate increased synaptic density and enhanced both short-term and long-term memory in preclinical models. The mechanism involves NMDA receptor function — magnesium sits in the channel of the NMDA receptor and acts as a voltage-dependent gate. When brain magnesium levels are adequate, NMDA receptor function improves, which enhances synaptic plasticity and reduces neural excitability. That reduction in excitability is exactly what helps you transition into sleep more smoothly.
Magnesium bisglycinate is the other form worth considering. It has good bioavailability, a calming effect through its glycine component, and some evidence for sleep improvement. The glycine itself acts as an inhibitory neurotransmitter, providing a complementary pathway to the NMDA modulation of threonate. Many people take both — threonate for the cognitive and sleep architecture effects, bisglycinate for the additional relaxation pathway.
Elemental Mg
145mg
Enzymatic Reactions
300+
Population Deficiency
50%