Magnesium — the mineral that runs the body.

Magnesium runs more than three hundred enzymatic reactions in the human body. Energy production. Muscle relaxation. Nerve signaling. The activation of vitamin D into its useful form. The balance with calcium that keeps every cell from going into spasm. The synthesis of glutathione, the body’s master antioxidant. The conversion of food into ATP, the molecule every cell uses to do work.

Without enough magnesium, none of those reactions run at full speed. Many of them stall.

The RDA is 400–420 mg per day for men, 310–320 mg for women. Surveys of actual American intake put the median at around 250 mg — well below the RDA, and the RDA itself was set to prevent obvious deficiency disease, not to optimize function. Dr. Mark Sircus has written for two decades that the optimal therapeutic dose sits closer to 500–1,000 mg per day, depending on body size and stress load.

That gap — between what the body needs and what people actually get — is what Sircus calls the magnesium deficit. It isn’t theoretical. The symptoms most people walk around with quietly are the symptoms of a body running on insufficient magnesium.

What deficiency actually looks like

Magnesium deficiency doesn’t usually announce itself with one big symptom. It accumulates as a pattern:

• Muscle cramps and twitches — eyelid twitch, calf cramps at night, restless legs
• Anxiety that doesn’t match the situation
• Difficulty falling asleep, or waking at 3 AM with the mind running
• Tension headaches and migraines
• Constipation
• High blood pressure that resists the usual interventions
• Heart palpitations or that “skipped beat” sensation
• Chronic fatigue with normal bloodwork
• Sensitivity to loud noises and bright lights
• Sugar cravings (the body craves what it needs to make insulin; magnesium is required)
• Heartburn and acid reflux (often misdiagnosed as too much acid, frequently too little)
• Premenstrual cramps and bloating

Standard blood tests for magnesium are nearly useless. Serum magnesium reflects what’s circulating in the blood, not what’s stored in tissue. Only about 1% of the body’s magnesium is in serum. A person can be profoundly tissue-deficient with a “normal” serum level.

The more accurate test is RBC magnesium — red blood cell magnesium — which measures what’s inside the cells, where magnesium actually works. Optimal range is 6.0–6.5 mg/dL. Most labs flag anything above 4.2 as “normal,” which is the threshold below which obvious deficiency disease starts. If you want a real answer, ask for RBC magnesium specifically. Most doctors will order it if you ask by name.

The forms problem

Walk into any drugstore and you’ll find magnesium oxide on the shelf. It’s the cheap one. It’s also nearly useless for correcting deficiency — its bioavailability is around 4%. What it does well is cause loose stool, which is why it’s the active ingredient in milk of magnesia.

The forms that actually correct deficiency are different. Each has a specialty:

• Magnesium glycinate (or bisglycinate) — magnesium bound to glycine. Highly absorbed, doesn’t cause loose stool, has a calming effect because glycine itself is an inhibitory neurotransmitter. The standard nighttime form. If you take one magnesium, take this one.
• Magnesium L-threonate (Magtein) — magnesium bound to threonic acid, developed specifically to cross the blood-brain barrier. The form that actually raises magnesium levels in the brain. Studied at MIT in the early 2010s; supports memory and cognitive function.
• Magnesium malate — magnesium bound to malic acid, a Krebs cycle intermediate. Useful for fibromyalgia, chronic fatigue, and muscle pain because malate supports ATP production.
• Magnesium citrate — decently absorbed, mildly laxative. A reasonable choice if you’re also constipated, but skip it if your bowels are already loose.
• Magnesium taurate — magnesium bound to taurine. Cardiovascular support, blood pressure, palpitations. The form Carolyn Dean recommends for heart-specific issues.
• Magnesium chloride — the form used in transdermal application (next section). Also available in liquid drops for oral use; absorbs well.
• Magnesium sulfate — Epsom salts. Limited oral use because of the sulfate (laxative), but excellent for baths.

The strategy is to combine the right forms for your specific situation, not to pick the cheapest one off the shelf.

Transdermal — Sircus’s signature framing

Dr. Mark Sircus’s specific contribution to the magnesium literature is the case for transdermal application. The argument is simple: oral magnesium has a real absorption ceiling. The gut can only take so much elemental magnesium at one time before the rest is excreted (or causes loose stool). For a person who’s significantly deficient and trying to repair years of low intake, oral alone is slow.

Transdermal application bypasses the gut entirely. Magnesium chloride dissolved in water — either as flakes in a bath, or as “magnesium oil” sprayed on the skin — is absorbed directly through the skin into the underlying tissue and bloodstream. There’s no upper limit imposed by intestinal threshold. You can saturate the skin and absorb a meaningful daily dose without the laxative effect.

Two practical forms:

• Magnesium flakes for baths or foot soaks. A cup of Life-Flo or Ancient Minerals magnesium flakes in a hot bath for 20–30 minutes. Two or three times a week is enough for most people.
• Magnesium oil sprayed on the skin after a shower. It’s actually a saturated magnesium chloride solution (not a true oil), and it tingles or stings on the first few applications until the skin adapts. Spray on legs, abdomen, forearms.

Sircus’s book Transdermal Magnesium Therapy is the long-form case if you want to read it directly. He argues transdermal magnesium is the fastest route to repleting a deficient body. The clinical experience of practitioners who use it backs that up.

Magtein for the brain

The L-threonate form deserves its own section because it’s the only oral magnesium that meaningfully raises brain magnesium levels. Most other forms support the body but don’t penetrate the blood-brain barrier well enough to matter for cognition.

Magtein was developed by researchers at MIT in 2010 specifically to address this. The clinical literature on it shows improvements in working memory, attention, and learning capacity in older adults. It isn’t a smart drug — it’s the restoration of a mineral that the brain runs on.

A typical dose is 2,000 mg of Magtein per day, which delivers about 144 mg of elemental magnesium specifically to the brain. It’s expensive ($30–50 per month). If your budget covers one premium magnesium product, this is the one to consider — but only after you have a baseline glycinate or transdermal practice in place. L-threonate isn’t a substitute for total-body repletion; it’s an addition.

Glycinate for sleep

If you sleep poorly, the simplest single change worth trying is 300–400 mg of magnesium glycinate at night, an hour before bed. Glycine itself acts on the GABA system; magnesium relaxes muscle and supports nervous-system downregulation. The combination is what makes glycinate the standard nighttime form.

Pure Encapsulations Magnesium Glycinate, Doctor’s Best High Absorption Magnesium (a glycinate-lysinate chelate), and KAL Magnesium Glycinate are the brands most often recommended. Skip any product that includes magnesium oxide as a filler — read the supplement-facts panel.

Dosing — how to actually correct a deficiency

For total-body repletion, working up over the first few weeks:

1. Start at 200–300 mg elemental magnesium per day. Glycinate works for everyone.
2. Add transdermal — a magnesium flake bath two or three times a week — for the next phase.
3. Build to 400–600 mg per day of elemental magnesium across forms, split into two doses (morning and night, or just at night if it’s purely glycinate).
4. Hold for 3–6 months. The body has decades of deficiency to make up.

The body will tell you if you’ve gone too high orally: loose stool. Back off. Add transdermal instead.

For people with chronic constipation, magnesium citrate is its own short-term solution. For people with anxiety or poor sleep, glycinate. For people with chronic muscle pain or fatigue, malate. For cognitive complaints, L-threonate added on top. For cardiovascular concerns, taurate.

Cofactors and the calcium question

Magnesium and calcium share regulatory pathways, and the modern American diet skews heavily toward calcium (fortified everything, dairy, supplements). The optimal calcium-to-magnesium ratio is roughly 1:1; many people are running at 5:1 or worse. Restoring magnesium often does more than calcium supplementation ever did.

Vitamin D activation requires magnesium. If you’ve been supplementing vitamin D and not seeing results, magnesium deficiency may be the bottleneck. K2 belongs in the stack with vitamin D — it directs calcium into bone instead of arteries.

B6 (in the P5P form) helps with magnesium retention. Adequate hydration helps. Reducing what depletes magnesium — caffeine, alcohol, refined sugar, chronic stress — helps as much as the supplementation does.

Where I buy magnesium

• Life-Flo Magnesium Flakes, 5 lb — for baths and foot soaks. Transdermal. One bag lasts months at two soaks a week.
• Ancient Minerals Magnesium Oil Spray — for daily transdermal application. Spray on legs, abdomen, forearms after a shower.
• Pure Encapsulations Magnesium Glycinate — for the nightly oral dose. Clean formulation, no oxide filler.
• Doctor’s Best Brain Magnesium with Magtein — for cognitive support. Optional add-on, only after the baseline is in place.
• Jigsaw Health Magnesium Malate — for energy or muscle pain support if those are your specific issues.

Where to start

A typical setup is magnesium glycinate, around 400 mg elemental, about an hour before bed; a magnesium chloride foot bath a couple of evenings a week (a few tablespoons of flakes in hot water, twenty minutes while reading); and magnesium oil sprayed on the legs after a hot shower in the mornings.

Kept consistent — and not skipped through travel or stressful weeks — the payoff tends to be deeper sleep, faster recovery from training, steadier mood, and small daily tensions that don’t accumulate the way they used to.

Closing

Magnesium is the kind of correction you can make to your body for about $30 a month that delivers more across more systems than almost any single intervention I know. It isn’t exotic. It isn’t new. It’s just the mineral that runs the body, and most of us aren’t getting enough of it.

Get an RBC magnesium test if you want a number to look at. Or just start glycinate at night, see what your sleep does in two weeks, and decide for yourself.