Summary
Magnesium is a critical mineral involved in over 300 biochemical reactions — from ATP energy production to muscle relaxation, nerve signalling, insulin action, and blood pressure regulation. It is one of the most commonly under-consumed minerals in modern diets, with deficiency linked to fatigue, muscle cramps, poor sleep, anxiety, and metabolic dysfunction.
Serum magnesium measures only about 1% of total body magnesium (the rest is in bone, muscle, and cells), meaning blood levels can appear normal while cellular deficiency causes significant symptoms. This limitation is important: serum magnesium stays within range until depletion is severe, making clinical symptoms and dietary assessment as important as the blood result.nnMagnesium is particularly relevant for people with type 2 diabetes (low magnesium worsens insulin resistance), cardiovascular disease (magnesium regulates cardiac rhythm), thyroid dysfunction (needed to activate vitamin D), and migraine sufferers (intravenous magnesium is an established acute treatment).
What It Is
Magnesium is the second most abundant intracellular cation (after potassium) and the cofactor for the enzyme ATP-synthase that powers virtually all energy-requiring reactions in the body. It is required for DNA and RNA synthesis, protein synthesis, muscle contraction and relaxation, nerve impulse transmission, bone mineralisation, and insulin receptor function.nnApproximately 50–60% of body magnesium is stored in bone, 20% in muscle, and the rest in soft tissues and cells. The kidneys tightly regulate serum magnesium by adjusting renal excretion, which means blood levels remain stable until total body depletion is significant.nnThe richest dietary sources include dark leafy greens (spinach, kale), nuts (almonds, cashews), seeds, legumes, dark chocolate, and wholegrains. Modern processed diets frequently fail to meet the recommended intake of 300–400 mg/day.
Functions
Energy production (ATP synthesis)
Magnesium is an essential cofactor for ATP synthase — the enzyme that produces virtually all cellular energy. Every ATP molecule must be bound to magnesium to be biologically active.
Muscle relaxation
Calcium drives muscle contraction; magnesium opposes this action and enables muscle relaxation. Deficiency causes cramps, spasm, and tension.
Nerve function and mood regulation
Regulates NMDA glutamate receptors, the GABA inhibitory system, and HPA stress axis activity — low magnesium is associated with anxiety, poor sleep, and depression.
Insulin sensitivity and blood sugar control
Required for insulin receptor function — magnesium deficiency worsens insulin resistance and is associated with higher type 2 diabetes risk.
Reference Ranges
Serum Magnesium
Measured in mmol/L| Status | Range (mmol/L) | What it means |
|---|---|---|
| Low | < 0.70 | Hypomagnesaemia — neuromuscular irritability, arrhythmia risk, and metabolic dysfunction. |
| Borderline | 0.70–0.80 | Low-normal — subclinical deficiency may still cause fatigue, cramps, and poor sleep quality. |
| Optimal | 0.80–1.05 | Adequate magnesium for normal enzymatic, neuromuscular, and metabolic function. |
| Elevated | > 1.05 | Hypermagnesaemia — rare from diet alone; investigate for renal insufficiency or excessive supplementation. |
Serum magnesium provides only a limited view of total body magnesium status. Normal serum levels do not exclude cellular deficiency. Symptoms and dietary assessment are equally important. Hypermagnesaemia from supplementation is rare but can be dangerous in people with kidney disease.
Symptoms of Imbalance
Magnesium deficiency produces a wide spectrum of symptoms affecting muscles, nerves, metabolism, and mental health.
- Muscle cramps, twitching, and spasms (particularly in calves and feet)
- Fatigue and low energy
- Poor sleep quality and insomnia
- Anxiety, irritability, and nervous tension
- Headaches and migraines
- Palpitations and irregular heartbeat
- Constipation
- Tingling or numbness in the hands and feet
- Hypermagnesaemia is rare and usually only seen with renal failure or massive supplementation
- Nausea and vomiting
- Low blood pressure and flushing
- Muscle weakness and reduced reflexes
- Slowed heart rate
- In severe cases: respiratory depression (acute toxicity)
Causes of Imbalance
- Low dietary intake — insufficient green vegetables, nuts, seeds, and wholegrains
- Type 2 diabetes (increased urinary magnesium excretion)
- Alcohol excess (reduces absorption and increases excretion)
- Chronic diarrhoea and malabsorption (coeliac, Crohn's)
- Proton pump inhibitors (impair magnesium absorption — long-term use)
- Diuretics (particularly loop diuretics and thiazides)
- Chronic stress (depletes intracellular magnesium)
- Renal failure (inability to excrete magnesium)
- Excessive magnesium supplementation
- Antacids or laxatives containing magnesium (in large amounts with kidney impairment)
- Rare: hypothyroidism or adrenal insufficiency
FAQs
Serum magnesium reflects only about 1% of total body magnesium. Blood levels are tightly maintained by the kidneys, which excrete or retain magnesium to keep serum levels stable even when cellular and bone stores are depleted. You can have significant cellular magnesium deficiency — causing real symptoms — with a serum level that appears within the laboratory reference range.
Magnesium glycinate (bisglycinate) is highly bioavailable and well-tolerated — making it a good choice for sleep, anxiety, and muscle cramps. Magnesium malate is often preferred for energy and fatigue. Magnesium citrate is affordable and effective but has a mild laxative effect. Magnesium oxide has low bioavailability and is best avoided. Typical doses range from 200–400 mg elemental magnesium at night.
Yes. Magnesium supplements can reduce absorption of certain antibiotics (fluoroquinolones, tetracyclines), bisphosphonates (osteoporosis medications), and some diabetes medications. Leave a 2-hour gap between magnesium supplements and these medications. Very high doses can lower blood pressure — relevant for people on antihypertensive medication.
Yes. Both oral magnesium supplementation (prophylaxis) and intravenous magnesium (acute treatment) have clinical evidence for migraine management. NICE and the European Headache Federation include magnesium in migraine prevention guidelines. A target serum magnesium of 0.85–0.95 mmol/L is commonly recommended in migraine management.
People at highest risk include: those with type 2 diabetes, heavy alcohol users, people taking long-term proton pump inhibitors or loop diuretics, anyone with gastrointestinal malabsorption, older adults, and people with chronically high stress levels. Athletes can also deplete magnesium through sweat, particularly in hot conditions.
References
- DiNicolantonio JJ, et al. Subclinical magnesium deficiency: a principal driver of cardiovascular disease and a public health crisis. Open Heart. 2018;5(1):e000668. View source
- Barbagallo M, Dominguez LJ. Magnesium and type 2 diabetes. World J Diabetes. 2015;6(10):1152–1157. View source
- Boyle NB, et al. The effects of magnesium supplementation on subjective anxiety and stress. Nutrients. 2017;9(5):429. View source