Magnesium Deficiency: Symptoms, Causes, and What You Should Know

What Magnesium Deficiency Actually Is

Magnesium deficiency, clinically called hypomagnesemia, occurs when your body does not have enough magnesium to carry out its essential functions. Magnesium is involved in more than 300 enzymatic reactions, including energy production, protein synthesis, muscle contraction, nerve signaling, and blood sugar regulation. When stores run low, nearly every system in the body is affected.

The challenge is that deficiency exists on a spectrum. Clinical deficiency severe enough to show up on a standard blood test is the extreme end. Functional deficiency, where cellular and bone stores are depleted but serum levels still appear normal, is far more common and far more difficult to diagnose.

Your body stores about 25 grams of magnesium in total. Roughly 60% is locked in bones, 39% inside muscle and soft tissue cells, and only about 1% circulates in the blood. This distribution is important because it means blood tests are a poor window into your actual magnesium status.

Why Blood Tests Often Miss Magnesium Deficiency

A serum magnesium test measures only the magnesium floating in your plasma, which is that small 1% fraction. Your body tightly regulates this number by pulling magnesium out of bones and cells whenever blood levels dip. This means serum magnesium can remain in the normal range even as your bone and intracellular stores are being steadily depleted.

A red blood cell (RBC) magnesium test measures magnesium inside red blood cells, which reflects intracellular levels more accurately than serum. Even this test is imperfect, but it is more sensitive to functional deficiency. Some specialists also use a magnesium loading test, where a measured dose of magnesium is given and urinary retention is assessed, to evaluate true body stores.

The Most Common Causes of Low Magnesium

Magnesium deficiency rarely has a single cause. In most people, several factors combine to push intake below the threshold needed to maintain healthy stores. Understanding your personal risk factors is the first step toward fixing the problem.

Dietary Insufficiency and Soil Depletion

Modern diets are low in magnesium-rich whole foods. Ultra-processed foods, refined grains, and fast food contain very little magnesium. Compounding this is the fact that intensive agricultural practices have depleted magnesium from topsoil over decades. Studies have found that the magnesium content of many vegetables and grains is significantly lower today than it was 50 years ago, meaning even people eating "healthy" may be getting less than they think.

Medications That Deplete Magnesium

Several widely prescribed medications reduce magnesium levels significantly. If you take any of these, your risk of deficiency is elevated and ongoing monitoring or supplementation may be warranted.

• Proton pump inhibitors (PPIs) such as omeprazole and esomeprazole reduce stomach acid, impairing magnesium absorption in the intestine. Long-term PPI use is one of the most common drug-induced causes of deficiency.
• Thiazide and loop diuretics increase urinary excretion of magnesium, directly draining stores. These are commonly prescribed for high blood pressure and heart failure.
• Metformin, the first-line diabetes medication, has been associated with lower serum magnesium levels, though the mechanism is not fully established.
• Certain antibiotics, particularly aminoglycosides, can cause significant renal magnesium wasting with prolonged use.
• Calcineurin inhibitors (cyclosporine, tacrolimus) used in transplant patients are known to cause magnesium wasting through the kidneys.

Poor Gut Absorption

Magnesium is absorbed primarily in the small intestine. Any condition that damages the gut lining or causes chronic diarrhea will reduce how much magnesium you absorb from food. Crohn's disease, celiac disease, irritable bowel syndrome with diarrhea, and short bowel syndrome all significantly increase deficiency risk. Even moderate chronic diarrhea from any cause accelerates magnesium loss.

Diabetes, Stress, and Alcohol

Type 2 diabetes causes excess urinary magnesium loss because high blood glucose levels trigger the kidneys to excrete more magnesium. This creates a damaging cycle: low magnesium impairs insulin sensitivity, and poor blood sugar control worsens magnesium loss. Chronic stress elevates cortisol, which increases urinary magnesium excretion. Excessive alcohol intake impairs magnesium absorption and increases renal losses simultaneously.

Symptoms to Know

Magnesium deficiency produces a wide range of symptoms because magnesium is involved in so many body processes. Symptoms tend to be vague early on, which is why deficiency often goes unrecognized for months or years. For a detailed breakdown of each symptom, see our guide to signs of magnesium deficiency.

• Muscle cramps and spasms, especially at night (most common early symptom)
• Fatigue and low energy, even with adequate sleep
• Poor sleep quality and difficulty falling asleep. Read more in magnesium and sleep
• Anxiety, irritability, and low mood, linked to magnesium's role in GABA and serotonin pathways
• Headaches and migraines: low magnesium is found in the brains of migraine sufferers
• Heart palpitations: irregular heartbeat is one of the most serious symptoms of deficiency
• Constipation: magnesium helps maintain bowel movement rhythm
• Numbness or tingling in hands, feet, or face
• High blood pressure: magnesium relaxes blood vessel walls
• Increased sensitivity to noise, bright light, or stress

Severe or prolonged deficiency can cause more serious complications including cardiac arrhythmias, seizures, hypocalcemia (low calcium, since magnesium is needed to activate vitamin D which controls calcium), and hypokalemia (low potassium, as magnesium is required for potassium retention in cells).

Who Is Most at Risk

While magnesium deficiency can affect anyone eating a modern diet, certain groups face substantially higher risk. Identifying your risk category helps prioritize action.

Older adults are at particular risk for a compounding reason: stomach acid production decreases with age, and magnesium requires adequate stomach acid for proper absorption. Combined with higher rates of medication use and reduced dietary variety, deficiency in people over 65 is extremely common and often clinically overlooked.

How to Correct Magnesium Deficiency

Correcting magnesium deficiency requires a two-pronged approach: improving dietary intake to provide a consistent daily supply, and using supplementation to rebuild depleted stores. Neither strategy alone is as effective as both together. The full process takes time because magnesium must gradually refill bone and cellular stores.

Step 1: Maximize Magnesium From Food

Food-sourced magnesium is the most sustainable long-term strategy and comes with co-nutrients (fiber, phytonutrients) that enhance health outcomes beyond magnesium alone. For a comprehensive guide to the best dietary sources, see best food sources of magnesium. The highest-impact foods to add immediately are:

Step 2: Choose the Right Supplement Form

Not all magnesium supplements are equally effective. The form of magnesium determines how well it is absorbed, and the difference is dramatic. Magnesium oxide, the cheapest and most common form in drugstores, has only about 4% absorption. Chelated forms like magnesium glycinate offer 80% or higher absorption and are far more effective for rebuilding stores. For a detailed comparison of all supplement forms, read how to choose a magnesium supplement and magnesium glycinate vs citrate.

To understand exactly how much magnesium you should be getting based on your age, sex, and health conditions, read how much magnesium per day for detailed guidance.

When to See a Doctor

Most mild to moderate magnesium deficiency can be addressed with dietary changes and over-the-counter supplements. However, certain situations call for medical evaluation and potential intravenous (IV) magnesium therapy.

• You experience heart palpitations, irregular heartbeat, or chest discomfort. Seek immediate medical attention.
• You have seizures or severe neuromuscular symptoms. This is a medical emergency.
• You are taking medications known to deplete magnesium (PPIs, diuretics, metformin) and have symptoms of deficiency. Ask your doctor to monitor your levels.
• You have a gastrointestinal condition like Crohn's or celiac disease that impairs absorption. You may need higher supplemental doses or IV administration.
• Symptoms do not improve after 8-12 weeks of consistent dietary and supplement intervention.
• You want a baseline blood test to track your magnesium status over time.

If you are addressing deficiency primarily through diet and supplementation, tracking symptoms in a simple journal (sleep quality, energy, cramp frequency, mood) gives you useful feedback over the 3-6 month repletion window, even without repeated blood tests.

Magnesium is involved in more than 300 enzymatic processes. It is not a niche nutrient. It is foundational.

NIH Office of Dietary Supplements

For related reading, explore our guides on signs of magnesium deficiency, how magnesium and sleep are connected, and the best food sources of magnesium to build an effective nutrition strategy around this essential mineral.