Symptoms of magnesium deficiency can range from subtle fatigue and muscle cramps to serious complications including seizures and cardiac arrhythmias. Magnesium deficiency, or hypomagnesaemia, occurs when serum magnesium falls below 0.7 mmol/L, affecting multiple body systems due to magnesium's role in over 300 enzymatic reactions. Whilst true deficiency is uncommon in healthy individuals, certain medical conditions, medications, and dietary factors significantly increase risk. Early recognition of symptoms is essential, as magnesium deficiency often coexists with other electrolyte imbalances and may require prompt medical assessment. This article explores the clinical features, risk factors, and evidence-based management approaches for magnesium deficiency in UK clinical practice.

What Is Magnesium Deficiency?

Magnesium deficiency, clinically termed hypomagnesaemia, occurs when serum magnesium levels fall below the normal reference range of 0.7–1.0 mmol/L. Magnesium is the fourth most abundant cation in the body and the second most abundant intracellular cation after potassium. It serves as a cofactor for over 300 enzymatic reactions, playing crucial roles in protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation.

True magnesium deficiency is relatively uncommon in healthy individuals consuming a balanced diet, as the kidneys efficiently regulate magnesium excretion. The body maintains tight homeostatic control of magnesium through intestinal absorption and renal excretion, with approximately 99% of total body magnesium stored in bone, muscle, and soft tissues, leaving only 1% in extracellular fluid.

Diagnosis can be challenging because serum magnesium levels do not always accurately reflect total body magnesium stores. A person may have depleted intracellular magnesium whilst maintaining normal serum levels initially. For this reason, clinical assessment must consider both biochemical measurements (serum magnesium, kidney function, calcium and phosphate) and presenting symptoms. Severity is typically graded as mild (0.5–0.7 mmol/L), moderate (0.4–0.5 mmol/L) or severe (<0.4 mmol/L).

When magnesium levels become significantly depleted, multiple organ systems can be affected, leading to neuromuscular, cardiovascular, and metabolic disturbances. Seek urgent medical attention if you experience seizures, fainting, chest pain, or severe palpitations with dizziness, particularly if you have risk factors for magnesium deficiency.

Common Symptoms of Magnesium Deficiency

The clinical presentation of magnesium deficiency varies considerably depending on the severity and duration of depletion. Early or mild deficiency may produce subtle, non-specific symptoms that are easily overlooked or attributed to other causes. These include:

• Fatigue and weakness – a general sense of tiredness and reduced energy levels

• Loss of appetite – decreased interest in food, which may further compromise nutritional intake

• Nausea – mild gastrointestinal discomfort without specific cause

As deficiency progresses to moderate or severe levels, more distinctive neuromuscular symptoms emerge. Muscle cramps, particularly affecting the legs and feet, are among the most commonly reported complaints. Patients may experience muscle twitching (fasciculations), tremor, or generalised muscle weakness. These symptoms reflect magnesium's essential role in neuromuscular transmission and muscle contraction.

Neurological manifestations can include paraesthesia (tingling or numbness), typically in the extremities, and in severe cases, seizures may occur. Personality changes, apathy, or increased irritability have also been documented, though these are less specific.

Cardiovascular symptoms represent potentially serious complications of magnesium deficiency. Cardiac arrhythmias, including atrial fibrillation, ventricular tachycardia, and typical ECG changes (prolonged QT interval), may develop. The prolonged QT interval increases risk of a dangerous arrhythmia called torsades de pointes. Patients might experience palpitations or irregular heartbeat sensations.

It is important to note that magnesium deficiency rarely occurs in isolation. It frequently coexists with other electrolyte disturbances, particularly hypokalaemia (low potassium) and hypocalcaemia (low calcium), which can be refractory to treatment until magnesium levels are corrected. This interrelationship can complicate the clinical picture and influence symptom presentation.

Call 999 or attend A&E immediately if you experience chest pain, new seizures, collapse/fainting, or severe palpitations with dizziness. For other persistent or concerning symptoms, contact your GP promptly for assessment.

Who Is at Risk of Low Magnesium Levels?

Several population groups and clinical conditions predispose individuals to magnesium deficiency. Understanding these risk factors is essential for early identification and prevention.

Gastrointestinal disorders represent a major risk category. Conditions causing chronic diarrhoea, malabsorption, or fat malabsorption significantly impair magnesium absorption. These include:

• Inflammatory bowel disease (Crohn's disease and ulcerative colitis)

• Coeliac disease

• Chronic pancreatitis

• Patients who have undergone bowel resection or bariatric surgery

• Chronic laxative use or misuse

Renal losses constitute another important mechanism. Type 2 diabetes mellitus, particularly when poorly controlled, increases urinary magnesium excretion through osmotic diuresis. Diabetic ketoacidosis can cause acute depletion. Chronic kidney disease in its early stages may also cause magnesium wasting, though advanced kidney disease can paradoxically lead to magnesium retention. Other conditions include primary hyperaldosteronism and genetic tubulopathies like Gitelman or Bartter syndrome.

Medication use is a frequently overlooked but significant risk factor. Proton pump inhibitors (PPIs), when used long-term, may reduce magnesium absorption. The MHRA advises that magnesium levels should be checked before and periodically during prolonged treatment with PPIs, especially when used with digoxin or drugs that may cause hypomagnesaemia (e.g., diuretics). Loop and thiazide diuretics increase renal magnesium losses. Other implicated medications include certain antibiotics (aminoglycosides), chemotherapy agents (cisplatin), and immunosuppressants (calcineurin inhibitors such as tacrolimus).

Alcohol use disorder impairs magnesium absorption, increases renal excretion, and is often associated with poor nutritional intake, creating multiple pathways to deficiency.

Elderly individuals face increased risk due to reduced dietary intake, decreased intestinal absorption, increased renal losses, and polypharmacy. Similarly, pregnant and lactating women have increased magnesium requirements that may not be met through diet alone, though routine supplementation is not recommended without clinical indication.

Other risk groups include patients with endocrine disorders (particularly hyperparathyroidism and hyperthyroidism), refeeding syndrome, post-parathyroidectomy (hungry bone syndrome), and severe burns. If you belong to any of these risk groups, discuss magnesium monitoring with your healthcare provider, particularly if you develop suggestive symptoms.

Treatment Options for Magnesium Deficiency

Management of magnesium deficiency depends on severity, underlying cause, and the presence of symptoms. The primary goals are to restore normal magnesium levels, address the underlying cause, and prevent recurrence.

Oral magnesium supplementation is the preferred first-line treatment for mild to moderate deficiency in patients who can tolerate oral intake. Various formulations are available, including magnesium oxide, magnesium citrate, magnesium glycinate, and magnesium chloride. The typical replacement dose ranges from 10–20 mmol of elemental magnesium daily (approximately 240–480 mg), usually given in divided doses. Dosing should be individualised based on serum levels and clinical response.

The main limitation of oral supplementation is gastrointestinal side effects, particularly diarrhoea, which occurs in a dose-dependent manner. Starting with lower doses and gradually increasing, or dividing the daily dose, may improve tolerance. Patients should be advised to take magnesium supplements with food to enhance absorption and reduce gastrointestinal upset. If you experience side effects that you suspect are related to magnesium supplements, report them via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

Magnesium supplements can interact with several medications. Take magnesium supplements at least 2-3 hours apart from tetracycline or quinolone antibiotics, bisphosphonates, levothyroxine, and iron supplements. Always check with your pharmacist about potential interactions.

Intravenous magnesium replacement is reserved for severe deficiency, symptomatic patients (particularly those with seizures or cardiac arrhythmias), or those unable to tolerate or absorb oral preparations. Hospital admission is typically required for IV administration, with careful cardiac monitoring, observation of deep tendon reflexes, and respiratory rate monitoring due to the risk of hypermagnesaemia during rapid correction.

Dietary optimisation should complement supplementation. Magnesium-rich foods include:

• Green leafy vegetables (spinach, kale)

• Nuts and seeds (almonds, pumpkin seeds)

• Whole grains

• Legumes (black beans, chickpeas)

• Dark chocolate

• Avocados

Addressing underlying causes is crucial for long-term management. This may involve optimising control of diabetes, reviewing and potentially adjusting medications contributing to magnesium loss, treating gastrointestinal disorders, or addressing alcohol use disorder. For patients on long-term PPIs or diuretics where discontinuation is not feasible, regular monitoring of magnesium levels is recommended, with supplementation only if deficiency is confirmed and under medical supervision.

Monitoring and follow-up should include repeat serum magnesium measurements, typically 1–2 weeks after initiating treatment, with adjustment of supplementation accordingly. Concurrent electrolyte abnormalities, particularly potassium and calcium, must be identified and corrected simultaneously, as hypokalaemia may be refractory to treatment until magnesium is repleted.

Patients should be counselled about realistic expectations—symptom improvement may take several weeks of consistent supplementation. If symptoms persist despite adequate replacement, alternative diagnoses should be considered. Always consult your GP before starting magnesium supplements, particularly if you have kidney disease (especially if eGFR <30 mL/min/1.73 m²), heart conditions, or take regular medications.

Frequently Asked Questions