Can Magnesium Supplements Really Reach Your Brain?

Most of us rarely think about how much magnesium we consume, yet our bodies cannot function without it. The average body contains about 25 grams of magnesium, more than half of it stored in the bones. The rest is distributed throughout the body’s cells, where it supports hundreds of essential chemical reactions—including the production of DNA and proteins and the transmission of signals through the nervous system, between the brain and the rest of the body.

But the fact that cells—especially neurons—need magnesium does not mean that taking extra magnesium will make them work better. Nor does consuming more of a substance guarantee that it will reach the brain or any other specific part of the body.

How magnesium supplements are absorbed

In supplements, magnesium is usually not present by itself. Instead, it is part of a compound known as a magnesium salt. The salt must dissolve before it can release Mg²⁺, the ionic form of magnesium used by the body. How much magnesium is absorbed or excreted depends on several factors, including the dose, the contents of the stomach and how much magnesium is already in the body. In general, a higher dose results in a lower proportion being absorbed.

Why magnesium oxide often acts as a laxative

That is assuming the supplement dissolves in the first place. Magnesium oxide is commonly used because it is an inexpensive tablet ingredient, but it does not break down particularly easily. In practice, magnesium oxide supplements often act primarily as laxatives, drawing water into the intestines and helping flush out excess salt.

Magnesium citrate and claims about bioavailability

This is where marketing enters the picture. Some other magnesium compounds dissolve more readily. For example, magnesium citrate has demonstrated the highest bioavailability in clinical tests. Although all these salts eventually break down in the intestines, some supplement labels claim that particular chemical formulations can deliver magnesium directly to specific parts of the body, including the muscles and brain.

What the evidence says about magnesium L-threonate

Those claims are often based on rodent experiments, in which animals are typically given higher doses of magnesium for longer periods than people taking tablets. In one rat study, a salt called magnesium L-threonate increased the amount of magnesium in the brain and improved some measures of learning and memory. This research helped inspire more enthusiastic marketing claims that magnesium L-threonate can transport magnesium directly to the brain.

Some human studies exist, but the evidence remains limited. Several small randomized trials have reported improvements in certain cognitive tests and measures of sleep, but they have important limitations. Some tested mixtures of substances, lasted only a few weeks or assessed very few outcomes. Many were funded by or conducted with the involvement of supplement manufacturers and therefore cannot be considered fully independent.

Can brain-focused magnesium supplements increase brain magnesium?

The studies also did not measure the amount of magnesium in the brain, for understandable reasons. So although magnesium L-threonate may penetrate gray matter somewhat more effectively, scientific understanding of how these salts are processed suggests that brain-focused magnesium supplements may still be little more than expensive laxatives.

This story was originally published by WIRED Czech Republic and Slovakia, translated from Czech.