Magnesium: the supplement you are probably deficient in

You eat reasonably well. You’re not surviving on fast food. And yet there’s a roughly 50% chance you’re not getting enough magnesium — a mineral involved in over 300 enzymatic reactions in your body. Not a trendy adaptogen, not a biohack. A fundamental mineral that your cells need to produce energy, regulate nerve function, maintain blood sugar, and contract muscles. The gap between what you need and what you’re getting is bigger than almost any other micronutrient, and it explains more everyday symptoms than most people realize.

Why deficiency is so common

Magnesium deficiency isn’t rare in the way scurvy is rare. It’s common in the way vitamin D deficiency is common — widespread, under-diagnosed, and driven by modern life.

Soil depletion. The magnesium content of fruits and vegetables has declined significantly over the past 60 years. Intensive farming practices strip magnesium from soil faster than it’s replenished. A serving of spinach in 1950 contained roughly twice the magnesium of a serving grown today. You’d need to eat significantly more produce to hit the same intake your grandparents did: Zhang W et al., Int J Vitam Nutr Res (2025) — https://pubmed.ncbi.nlm.nih.gov/41504160/.

Absorption issues. Even when you eat magnesium-rich foods, absorption varies. Gut health matters — conditions like IBS, celiac disease, and chronic inflammation reduce absorption. The form of magnesium in food also matters. Leafy greens and nuts contain magnesium bound to oxalates and phytates, which reduce bioavailability. You might be eating the right foods and still not absorbing enough.

Increased demand. Stress, exercise, alcohol, and certain medications increase magnesium requirements. If you’re training hard, dealing with chronic stress, or taking proton pump inhibitors for acid reflux, your body is burning through magnesium faster than average.

The blood test problem. Standard serum magnesium tests measure only about 1% of your body’s total magnesium stores. The other 99% is stored in bones and tissues. Your blood test can come back “normal” while you’re significantly depleted at the cellular level. This is why so many people walk around deficient without knowing it — the test that would catch it isn’t the one your doctor orders.

What magnesium actually does

This isn’t a “might help with energy” supplement. Magnesium is a cofactor for over 300 enzymatic reactions. Here’s what that means in practical terms.

Energy production. Every cell in your body produces energy through ATP (adenosine triphosphate). Magnesium is required for ATP to function. Without adequate magnesium, your cells literally can’t produce energy efficiently. This is why fatigue is the most common — and most overlooked — symptom of deficiency.

Nerve function. Magnesium regulates the NMDA receptor, which is involved in nerve signal transmission. When magnesium is low, NMDA receptors become overactive, leading to heightened neural excitability. This manifests as anxiety, irritability, muscle twitches, and that “wired but tired” feeling where your body is exhausted but your brain won’t stop: Touyz RM et al., N Engl J Med (2024) — https://pubmed.ncbi.nlm.nih.gov/38838313/.

Blood sugar regulation. Magnesium is involved in insulin signaling and glucose metabolism. Low magnesium impairs insulin sensitivity, which means higher blood sugar after meals, more insulin secretion, and eventually a cycle that contributes to insulin resistance. This connection is particularly relevant if you’re dealing with blood sugar issues or metabolic changes in your 40s.

Muscle function. Magnesium allows muscles to relax after contraction. Calcium triggers contraction; magnesium triggers relaxation. When magnesium is low, muscles stay partially contracted — causing cramps, spasms, tension, and that tight feeling in your shoulders and neck that never quite goes away.

Sleep. Magnesium’s effect on sleep works through GABA receptor modulation and cortisol regulation. It calms the nervous system and reduces the “racing mind” effect. The form matters significantly for sleep — not all magnesium supplements help you sleep the same way.

How much you actually need

The Recommended Dietary Allowance (RDA) for magnesium is 310–320 mg/day for women and 400–420 mg/day for men. These numbers are based on preventing deficiency symptoms, not optimizing function. Most researchers studying magnesium argue the optimal intake is higher — closer to 500–600 mg/day for active adults.

To put this in food terms:

Getting 400+ mg from food alone is technically possible but requires deliberate effort. You’d need to eat pumpkin seeds, almonds, spinach, and beans every single day. Most people don’t, which is why supplementation becomes practical.

Which form to take

Not all magnesium supplements are created equal. The form determines how well it’s absorbed and what it does.

Magnesium glycinate. Best for: sleep, anxiety, general supplementation. Glycinate is magnesium bound to the amino acid glycine, which itself has calming properties. High bioavailability, gentle on the stomach. This is the default recommendation for most people: Magnesium Glycinate with Zinc.

Magnesium L-threonate. Best for: cognitive function, brain health. This form crosses the blood-brain barrier more effectively than others. Research suggests it may improve sleep architecture — not just sedation, but actual time in deep and REM sleep: Magnesium L-Threonate — Neuro-Mag.

Magnesium citrate. Best for: constipation relief. Higher doses have an osmotic laxative effect. Good if you need both magnesium and bowel regularity. Not ideal for general supplementation because the laxative effect limits how much you can take.

Magnesium oxide. Worst for: almost everything. This is the cheapest form and the most common in drugstore supplements. Bioavailability is around 4% — meaning 96% passes through your body unabsorbed. If your magnesium supplement isn’t working, check if oxide is the form.

Magnesium taurate. Best for: cardiovascular support. Taurine and magnesium together support heart rhythm and blood pressure regulation. Less studied than glycinate but promising for cardiovascular health.

What to stop doing

Stop buying the cheapest magnesium at the drugstore. If it’s magnesium oxide, you’re paying for expensive urine. Check the form on the label.

Stop taking magnesium with calcium at the same time. Calcium and magnesium compete for absorption. Take them at least 2 hours apart. If you’re taking a calcium-magnesium combo supplement, the ratio matters — you want at least 2:1 calcium to magnesium, but most people need more magnesium, not less.

Stop ignoring symptoms you’ve normalized. Muscle cramps, afternoon fatigue, difficulty falling asleep, anxiety that doesn’t respond to lifestyle changes, 3 AM wake-ups — these are common, but common doesn’t mean normal. If you’ve chalked them up to “just getting older” or “just stress,” magnesium deficiency is worth exploring.

What we still don’t know

The optimal magnesium form for specific conditions is still being studied. We know glycinate works well for sleep and general use, and L-threonate shows promise for cognition, but head-to-head comparisons between forms are sparse. Most studies compare magnesium to placebo, not one form to another. The clinical differences between forms are largely based on absorption data and mechanistic reasoning rather than direct outcome comparisons.

We also don’t fully understand how magnesium interacts with other minerals at the cellular level. The calcium-magnesium-zinc triangle is well-documented at the absorption level, but how these interactions play out over years of supplementation is less clear.

Start with 200–400 mg of magnesium glycinate before bed. Give it 3–4 weeks. If your sleep improves, your cramps ease, or your baseline anxiety drops, you had your answer. Send this to someone who’s tired all the time and can’t figure out why.