Magnesium takes part in more than 300 biochemical reactions: energy synthesis (ATP), the work of nerves and muscles, heart rhythm, glucose metabolism. It is one of the most "underrated" electrolytes.
An important nuance: only about 1% of the body's magnesium is in the blood, the rest is in bones and cells. So normal blood magnesium does not rule out a deficiency in the tissues — especially with insulin resistance, diabetes, diuretic use and alcohol abuse.
Reference ranges
The reference range depends on the lab; a typical range for adults:
| Adults (serum) | 0.70 – 1.00 mmol/L |
| Mild deficiency | 0.5 – 0.7 mmol/L |
| Clinically significant | < 0.5 mmol/L |
| Hidden deficiency | symptoms with a normal test (intracellular) |
| Elevation | usually with kidney failure |
What an elevated level means
High magnesium (hypermagnesemia) is rare and almost always linked to reduced kidney function: the kidneys stop clearing the excess, especially against a background of magnesium supplements or magnesium-containing antacids and laxatives.
Symptoms appear with a marked rise: nausea, weakness, a drop in blood pressure, slowed reflexes; in severe cases — breathing and heart rhythm disturbances.
What a low level means
Magnesium deficiency (hypomagnesemia) is a far more common problem.
Causes: losses through the gut (diarrhea, malabsorption) and the kidneys, chronic use of proton pump inhibitors and diuretics, alcohol abuse, diabetes and insulin resistance, and a poor diet.
Symptoms: muscle cramps and twitching, fatigue, irritability, sleep disturbances, palpitations. Magnesium deficiency also makes it hard to restore calcium and potassium.
How the test is done
Magnesium is measured in blood serum from a vein, preferably fasting. Remember the method's limitation: the blood test can be normal despite a tissue deficiency.
It makes sense to interpret magnesium together with calcium and potassium: their metabolism is closely linked, and a persistent deficiency of one often goes hand in hand with another.
What affects the value
- Proton pump inhibitors and diuretics — a common cause of hidden deficiency with long-term use.
- Alcohol — increases magnesium losses through the kidneys.
- Diabetes and insulin resistance — accompanied by intracellular deficiency.
- GI diseases (diarrhea, malabsorption) — losses through the gut.
- Kidney function — when it declines, magnesium instead accumulates.
- Hemolysis of the sample — overstates the result (magnesium leaks out of cells).
Assess insulin resistance
Magnesium deficiency is closely linked to insulin resistance — assess it from your labs:
Frequently asked questions
Blood magnesium is normal — does that mean there is no deficiency?
Not necessarily. Only about 1% of the body's magnesium is in the blood, so a serum test can be normal despite a deficiency in the cells. With characteristic symptoms (cramps, fatigue) and risk factors (diuretics, PPIs, alcohol, diabetes) a deficiency is likely even when the test is "normal".
Which magnesium is best to take?
In the absence of kidney disease, organic forms (citrate, glycinate, malate) are usually preferred — they are absorbed better and are gentler on the gut than oxide. But the dose and the need are best judged by symptoms and risk factors, and with kidney disease — only with a doctor.
How are magnesium and blood sugar related?
Magnesium deficiency impairs the action of insulin on cells and is linked to insulin resistance and metabolic syndrome. And conversely: in diabetes magnesium is lost more actively. That is why magnesium is often considered in the context of carbohydrate metabolism.
Related terms
Sources
- MedlinePlus (NIH) — Magnesium Blood Test
- Hypomagnesemia — StatPearls (NCBI)
- Magnesium, insulin resistance and metabolic syndrome (review). NCBI/PMC