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Magnesium

Magnesium is a mineral involved in energy production, muscle function, and nerve signalling.

What is Magnesium?

Magnesium plays a role in hundreds of processes — from energy production and muscle relaxation to nerve signalling and bone metabolism. Nearly all body magnesium sits inside cells and bones; only about 1% circulates in the blood. That makes the blood value a limited reflection of your actual stores. A normal blood level does not rule out a functional deficiency. Factors that deplete magnesium: long-term use of acid suppressants or diuretics, alcohol, and impaired gut absorption. Symptoms like muscle cramps, poor sleep, and irritability can point to a deficiency even when the serum looks normal.

Why is Magnesium relevant?

Magnesium is a key mineral for energy and recovery. A deficiency can contribute to chronic fatigue, reduced exercise tolerance, and slow muscle recovery — complaints that are correctable when magnesium is the cause. Magnesium also has a direct effect on potassium: with a magnesium deficiency the kidney spills potassium, so a low potassium will not recover with potassium supplementation until magnesium is restored. Always read both values together.

Magnesium high or low — what it means

Read magnesium alongside potassium and calcium. A low potassium that does not respond to supplementation is a strong pointer to a magnesium deficiency. With declining kidney function (low eGFR) the risk of too-high magnesium rises; with diuretic use the risk runs the other way. When starting supplementation, retest after 6–8 weeks — cellular stores need time to replenish. Magnesium glycinate and malate are generally better tolerated than magnesium oxide.

Magnesium reference ranges

Normal (adults)Adult reference range (>16 years) per the NVKC and Dutch labs (e.g. OLVG).0.70-1.00 mmol/L
LowHypomagnesaemia; mild to moderate deficiency.< 0.70 mmol/L
Severely lowClinically significant deficiency; symptoms usually appear only below this level and correction is needed.< 0.50 mmol/L
HighHypermagnesaemia; usually from reduced renal excretion or magnesium intake.> 1.00 mmol/L

Cut-offs vary by lab and method — the reference range on your own lab report is always leading. The blood value reflects only ~1% of total body magnesium (the rest is inside cells and bones), so a normal value does not fully rule out a functional deficiency.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

Read about our scientific approach →Read the guide: Supplements →

Frequently asked questions

What is a normal magnesium level in blood?

For adults the normal range is 0.70 to 1.00 mmol/L (NVKC and Dutch labs such as OLVG). Note that the blood value only shows about 1% of your total body magnesium — the rest is stored inside cells and bones. A value within range therefore does not fully rule out a mild deficiency. The reference range on your own lab report is always leading, as it can vary slightly between labs and methods.

What does a low magnesium mean?

A value below 0.70 mmol/L is called hypomagnesaemia; below 0.50 mmol/L it is a severe, clinically significant deficiency at which symptoms usually start to appear. Common causes include long-term use of acid suppressants or diuretics (water pills), alcohol use, prolonged diarrhoea, poor gut absorption (for example in Crohn's disease), and insufficient dietary intake. Symptoms can include muscle cramps, fatigue, poor sleep, and irritability.

What does a high magnesium mean?

A value above 1.00 mmol/L (hypermagnesaemia) is rarely caused by diet. The usual cause is reduced excretion by the kidneys (kidney failure) or magnesium intake, for example through laxatives or supplements. It can also occur with dehydration or an overactive parathyroid. With reduced kidney function, caution with magnesium supplementation is warranted.

When is a magnesium level concerning?

A severely low magnesium (< 0.50 mmol/L) or a markedly high value can affect heart rhythm and nerve and muscle function and warrants medical assessment. A low potassium that does not recover with supplementation often points to a magnesium deficiency — read both values together. If you start supplementation, retest only after 6-8 weeks, because cellular stores need time to replenish.

Related biomarkers

Potassium
Potassium is an electrolyte that is essential for your heart rhythm, muscle function and nerve signaling.
Calcium
Mineral essential for bone formation, muscle function, and nerve signaling.

Magnesium is one of the biomarkers in the Optimize blood test. Book a blood draw at any of 238+ partner labs in the Netherlands, or upload your existing results in the app.

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