Here’s something that’ll ruin your morning: there’s a good chance you’re magnesium deficient right now. Not “maybe, if you eat poorly” deficient — the NHANES data from 2005-2006 showed that 68% of Americans consume less than the RDA for magnesium. A more recent analysis published in Open Heart (2018) called it a public health crisis hiding in plain sight.

And the thing is, you won’t catch it on a standard blood test. Serum magnesium — the test your doctor orders — only measures the 1% of your total magnesium that’s floating around in your blood. The other 99% is in your bones, muscles, and cells. You could be severely depleted and your bloodwork would look fine.

Why You’re Probably Not Getting Enough

Three factors are working against you simultaneously.

First, soil depletion is real and measurable. A landmark study comparing USDA nutrient data from 1950 to 1999 found significant declines in magnesium content across 43 crops (Journal of the American College of Nutrition, 2004). The spinach your grandmother ate was legitimately more nutritious than yours.

Second, processed food is stripped of magnesium during refining. White flour loses roughly 80% of its magnesium compared to whole grain. If you eat anything that comes in a box, you’re fighting an uphill battle.

Third — and this is the one nobody talks about — stress depletes magnesium, and magnesium depletion increases stress. It’s a feedback loop. Cortisol causes your kidneys to excrete more magnesium. Less magnesium means your nervous system runs hotter. Which produces more cortisol. Rinse, repeat.

The Form Problem

Walk into any supplement store and you’ll find fifteen different forms of magnesium. Most of them are a waste of money.

Magnesium oxide is the most common form because it’s dirt cheap to manufacture. It’s also terribly absorbed — bioavailability around 4% according to a study in the Journal of the American College of Nutrition (2001). You’re essentially buying an expensive laxative.

Magnesium citrate is better. Decent absorption, well-studied, affordable. It’s a solid baseline choice if you just want to hit your RDA without overthinking it.

Magnesium glycinate is where things get interesting. The glycine chelate dramatically improves absorption and the glycine itself has calming properties. If sleep quality is a goal — and it should be — this is the form to take in the evening. I’ve been using it nightly for two years and the difference in my sleep latency was noticeable within the first week.

Magnesium L-threonate is the newest player and the most expensive. It’s the only form shown to cross the blood-brain barrier effectively, based on MIT research published in Neuron (2010). If cognitive performance matters to you, this is worth the premium — but treat it as a separate supplement from your baseline magnesium, not a replacement.

What I Actually Take

My current protocol is split dosing:

— 400mg magnesium glycinate in the evening, 30 minutes before bed (I use Pure Encapsulations) — 144mg magnesium L-threonate (as Magtein) in the morning for cognitive benefits

Total elemental magnesium: around 450mg daily, which puts me well above the RDA of 400-420mg for adult males.

I skip magnesium oxide entirely. Life’s too short for 4% bioavailability.

The Bottom Line

Stop guessing about magnesium. The odds are literally stacked against you — modern diets, depleted soils, and chronic stress create a near-universal deficiency that standard blood tests can’t catch.

Pick glycinate for sleep and general repletion. Add threonate if you care about cognitive performance. Skip oxide — it’s a relic of an era when nobody bothered to measure absorption.

Start tonight. You’ll probably notice the difference in your sleep within a week.