Magnesium: The Deficiency You Probably Have

It's involved in over 300 biochemical reactions in your body. You're almost certainly not getting enough. And it might explain why you can't sleep.

If there were an award for "Most Underappreciated Mineral," magnesium would win in a landslide. It doesn't have the marketing budget of vitamin D. It doesn't have the cultural cachet of iron. It quietly does its job in over 300 enzymatic reactions throughout your body — and most people are running on empty.

The numbers are alarming. Studies estimate that 50% of Americans consume less than the recommended daily amount of magnesium. And because modern farming practices have depleted magnesium from soil, even people who eat relatively well may not be getting what their grandparents got from the same foods.

Subclinical magnesium deficiency — meaning levels low enough to cause problems but not low enough to trigger obvious symptoms — has been called a "public health crisis" by researchers. And it touches nearly every system in your body.

What Magnesium Does (The Short Version: Everything)

Magnesium is a cofactor in over 300 enzyme systems. A cofactor is like a helper molecule — the enzyme can't do its job without it. Here's a partial list of what magnesium is involved in:

Energy production: Magnesium is required for ATP synthesis. Remember, ATP is the energy currency of every cell. Magnesium literally binds to ATP to make it functional. Without magnesium, your cells can't properly use energy.
DNA and protein synthesis: Every time your body makes new DNA or builds new proteins, magnesium is involved.
Muscle function: Magnesium regulates muscle contraction and relaxation. Calcium causes muscles to contract; magnesium helps them relax. Too little magnesium = muscles that cramp, twitch, and can't properly relax.
Nervous system regulation: Magnesium modulates neurotransmitter signaling and acts as a natural calcium channel blocker in neurons. It helps keep the nervous system calm rather than overexcited.
Blood pressure regulation: Magnesium relaxes blood vessel walls, helping maintain healthy blood pressure.
Blood sugar metabolism: Magnesium plays a key role in insulin signaling and glucose metabolism. Low magnesium is linked to insulin resistance and type 2 diabetes.
Bone health: About 60% of your body's magnesium is stored in bone. It's essential for bone formation and influences the activity of osteoblasts (bone-building cells) and osteoclasts (bone-breaking-down cells).

When researchers say magnesium is involved in "over 300 reactions," they're not exaggerating. It's one of the most widely used minerals in human biochemistry.

Why You're Probably Deficient

The Soil Problem

Magnesium content in crops has declined significantly over the past century. Industrial farming practices — particularly the heavy use of fertilizers that don't replace magnesium — have gradually depleted this mineral from agricultural soils. A tomato today contains measurably less magnesium than a tomato from 1950.

The Processing Problem

Food processing strips magnesium. When wheat is refined into white flour, roughly 80% of the magnesium is removed. When rice is polished to become white rice, most of the magnesium goes with the bran. The modern diet is built on processed, refined foods — which are magnesium-poor by design.

The Water Problem

Historically, drinking water was a significant source of magnesium, especially in areas with "hard" water. Modern water treatment and the widespread use of filtered and bottled water have removed this source for many people.

The Stress Problem

Physical and psychological stress increases magnesium excretion through urine. Alcohol does the same. So does caffeine, to a lesser degree. In other words, the modern lifestyle actively depletes magnesium while simultaneously providing less of it.

The Testing Problem

Here's the frustrating part: standard blood tests for magnesium are nearly useless for detecting deficiency. The typical serum magnesium test measures magnesium in your blood — but only 1% of your body's magnesium is in the blood. Your body tightly regulates blood magnesium by pulling it from bones and tissues, so serum levels can appear "normal" even when total body stores are severely depleted.

DiNicolantonio and colleagues published an influential review in 2018 arguing that subclinical magnesium deficiency is widespread and underdiagnosed precisely because of this testing limitation. They called it "a principal driver of cardiovascular disease and a public health crisis" (PMID: 29387426).

A red blood cell (RBC) magnesium test is somewhat more useful, but even that has limitations. The reality is that magnesium deficiency is primarily a clinical diagnosis — you suspect it based on symptoms, dietary history, and response to supplementation.

Magnesium and Sleep

If you struggle with sleep, pay attention to this section.

Magnesium plays a direct role in regulating the nervous system's transition from wakefulness to sleep. It activates the parasympathetic nervous system (the "rest and digest" mode), regulates the neurotransmitter GABA (which quiets brain activity), and helps regulate melatonin production.

Abbasi and colleagues conducted a double-blind, placebo-controlled trial in 2012 with elderly participants suffering from insomnia. Those who received 500 mg of magnesium daily for 8 weeks experienced significant improvements in sleep time, sleep efficiency, and melatonin levels, along with significant decreases in cortisol (the stress hormone). They also fell asleep faster (PMID: 23853635).

Other studies have confirmed these findings. Magnesium supplementation consistently improves subjective sleep quality, particularly in people with low baseline magnesium status — which, as we've established, is most people.

The effect isn't as dramatic as a sleeping pill. It's more subtle — a gradual improvement in sleep quality over weeks. But unlike sleeping pills, there's no dependency, no cognitive impairment, and the benefits come from correcting an actual deficiency rather than forcing your brain into unconsciousness.

Magnesium and Heart Health

Zhang and colleagues published a meta-analysis in 2016 examining the relationship between magnesium intake and cardiovascular risk. After pooling data from multiple large cohort studies, they found that higher magnesium intake was associated with significantly lower risks of:

Heart failure (22% lower risk)
Stroke (7% lower risk per 100 mg/day increase)
Type 2 diabetes (19% lower risk)
All-cause mortality (10% lower risk)

These are substantial risk reductions from a single, inexpensive mineral.

The mechanisms are well understood. Magnesium:

Relaxes blood vessel walls (lowering blood pressure)
Reduces arterial calcification
Improves endothelial function (the health of your blood vessel lining)
Reduces inflammatory markers
Improves insulin sensitivity (reducing metabolic syndrome risk)

Multiple studies have shown that magnesium supplementation reduces blood pressure by 3-4 mmHg systolic and 2-3 mmHg diastolic on average. That might sound small, but at a population level, even a 2 mmHg reduction in systolic blood pressure reduces stroke mortality by 10%.

The Different Forms: A Practical Guide

Not all magnesium supplements are created equal. The mineral must be bound to something else (a "chelate") to be absorbed, and the choice of chelate dramatically affects how well it works and what it's good for.

Magnesium Glycinate

Best for: Sleep, anxiety, general supplementation Bioavailability: High GI tolerance: Excellent (rarely causes loose stools)

Glycinate is magnesium bound to the amino acid glycine — which itself has calming, sleep-promoting properties. This double benefit makes it the top choice for people supplementing primarily for sleep and relaxation. It's gentle on the stomach and well-absorbed.

Magnesium L-Threonate

Best for: Brain health, cognitive function Bioavailability: Moderate GI tolerance: Good

Threonate is unique because it was specifically developed (by MIT researchers) to cross the blood-brain barrier effectively. Animal studies show it raises brain magnesium levels more effectively than other forms. If cognitive function and brain health are your primary goals, threonate is worth considering — though it's more expensive.

Magnesium Citrate

Best for: General supplementation, constipation Bioavailability: Good GI tolerance: Moderate (can cause loose stools at higher doses)

Citrate is well-absorbed and widely available. Its tendency to draw water into the intestines makes it useful for people who struggle with constipation — but this same property means it can cause digestive issues at higher doses.

Magnesium Oxide

Best for: Almost nothing (as a supplement) Bioavailability: Poor (only ~4% absorbed) GI tolerance: Poor (often causes digestive issues)

Oxide is the cheapest form and the one most commonly found in bargain supplements. Unfortunately, it's also the worst absorbed. Your body only takes in about 4% of magnesium oxide, compared to 20-30% or more for better forms. It's fine as a laxative, but it's a poor choice for correcting deficiency.

Magnesium Malate

Best for: Energy, muscle pain Bioavailability: Good GI tolerance: Good

Malate is magnesium bound to malic acid, which plays a role in the energy-producing citric acid cycle. Some research suggests it may be particularly helpful for fatigue and muscle pain.

How Much Do You Need?

The RDA for magnesium is:

Men: 400-420 mg/day
Women: 310-320 mg/day

Many researchers argue these numbers are too low and represent the minimum to prevent frank deficiency, not the optimal amount for health. Some longevity-focused practitioners recommend 400-600 mg/day total (from food + supplements).

From food: The best dietary sources are dark leafy greens (spinach, Swiss chard), nuts (almonds, cashews), seeds (pumpkin seeds are extraordinary — one ounce provides 37% of the RDA), dark chocolate, avocados, and legumes.

From supplements: Most people benefit from supplementing 200-400 mg of elemental magnesium daily (in addition to dietary intake). Start at the lower end and increase gradually to assess GI tolerance.

Timing: Magnesium glycinate or threonate taken 30-60 minutes before bed can support sleep quality. Otherwise, timing is flexible.

When to Be Cautious

Magnesium supplementation is extremely safe for most people. However:

Kidney disease: If you have significant kidney impairment, your kidneys may not be able to excrete excess magnesium properly. Consult your doctor.
Certain medications: Magnesium can interact with some antibiotics, bisphosphonates, and diuretics. If you take prescription medications, check with your pharmacist.
Too much at once: Taking large doses can cause diarrhea. Split your dose if needed.

The upper tolerable limit for supplemental magnesium is set at 350 mg/day — but this refers specifically to supplements, not food. And the main risk of exceeding it is GI discomfort, not toxicity.

What This Means For You

Magnesium deficiency is common, underdiagnosed, and remarkably easy to fix. Here's your playbook:

Assume you're probably low unless you eat an unusually mineral-rich diet (lots of leafy greens, nuts, seeds, and unprocessed foods).
Start supplementing with 200-400 mg of magnesium glycinate daily. It's cheap, safe, well-absorbed, and won't upset your stomach.
Take it before bed if sleep is a concern. The glycinate + magnesium combination is a natural sleep supporter.
Consider threonate if you're specifically interested in brain health and cognitive function, though it costs more.
Avoid magnesium oxide. It's cheap for a reason — your body barely absorbs it.
Eat magnesium-rich foods: A handful of pumpkin seeds, a serving of spinach, and a square of dark chocolate together provide over 200 mg of highly bioavailable magnesium.
Don't rely on blood tests to tell you if you're deficient. Serum magnesium is a poor marker. If you have symptoms of deficiency (poor sleep, muscle cramps, anxiety, fatigue, high blood pressure) and an imperfect diet, supplementation is a reasonable bet.

For a mineral that costs pennies per day and participates in hundreds of biological processes, the risk-reward calculation is overwhelmingly in your favor. Magnesium may not be glamorous, but fixing a deficiency you didn't know you had can be transformative.

🛒 Recommended Products

Affiliate Disclosure: Links below may earn us a commission at no extra cost to you. We only recommend products backed by the evidence discussed above.

Magnesium Glycinate — The best-absorbed, gentlest form. Ideal for daily use and sleep support. Look for 200–400mg elemental magnesium per serving.

Magnesium L-Threonate — Developed by MIT researchers to cross the blood-brain barrier. Best choice if brain health and cognitive function are your priority.

Sources

DiNicolantonio, J.J., O'Keefe, J.H., & Wilson, W. (2018). Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. Open Heart. PMID: 29387426
Abbasi, B., et al. (2012). The effect of magnesium supplementation on primary insomnia in elderly: A double-blind placebo-controlled clinical trial. Journal of Research in Medical Sciences. PMID: 23853635
Zhang, X., et al. (2016). Effects of magnesium supplementation on blood pressure and cardiovascular risk factors: A meta-analysis. Journal of Hypertension.
Slutsky, I., et al. (2010). Enhancement of learning and memory by elevating brain magnesium. Neuron. PMID: 20152124
Rosanoff, A., Weaver, C.M., & Rude, R.K. (2012). Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutrition Reviews. PMID: 22364157
Schwalfenberg, G.K., & Genuis, S.J. (2017). The Importance of Magnesium in Clinical Healthcare. Scientifica. PMID: 28210365