Clinically Reviewed by Dr. Andrew Stein MD, Consultant Physician. Last updated: April 2026
Magnesium is often called the “spark plug” of the body. While calcium provides the structural strength for bones, magnesium is the essential co-factor for over 300 biochemical reactions.
It is the silent partner that allows your body to produce energy, relax muscles, and maintain a steady heartbeat.
Because magnesium is involved in everything from DNA synthesis to muscle contraction, your body works hard to keep blood levels steady, primarily by adjusting how much the kidneys excrete or reabsorb.
For most healthy adults, a normal blood magnesium level is between 0.7 and 1.0 mmol/L (or 1.7 to 2.4 mg/dL).
Note: Only about 1% of your body’s total magnesium is found in the blood; the rest is tucked away in your bones and soft tissues. This means a blood test might occasionally show a “normal” level even if your body’s total stores are starting to run low.
Magnesium imbalances are categorised into two conditions. Because magnesium regulates the flow of other electrolytes like calcium and potassium, an imbalance here often causes a “domino effect” across your entire mineral profile.
| Condition | Level | Definition |
| Hypomagnesaemia | Below 0.7 mmol/L | Low blood magnesium |
| Hypermagnesaemia | Above 1.0 mmol/L | High blood magnesium |
Why do these levels matter?
Magnesium acts as a natural “calcium blocker.” In your muscles, calcium causes contraction, while magnesium allows the muscle to relax.
Low magnesium removes the “brakes,” leading to muscle spasms, tremors, and even dangerous heart rhythms (arrhythmias).
High magnesium acts as a powerful muscle relaxant; it can slow the heart and breathing to dangerous levels.
Low magnesium is quite common, especially in hospitalised patients. It is often the “hidden” cause behind stubborn low potassium or low calcium levels.
Gastrointestinal Issues: Conditions like Crohn’s disease, coeliac disease, or chronic diarrhoea prevent the gut from absorbing magnesium properly.
Alcohol Use Disorder: Alcohol acts as a diuretic that specifically “flushes” magnesium out through the kidneys.
Medications: Long-term use of Proton Pump Inhibitors (PPIs) for acid reflux or certain “loop” diuretics can significantly lower levels.
Type 2 Diabetes: High blood sugar causes the kidneys to excrete more urine, taking magnesium along with it.
Hypermagnesaemia is relatively rare because healthy kidneys are incredibly efficient at getting rid of excess. When it does occur, it is usually due to:
Kidney Disease: This is the most common cause. If the kidneys aren’t filtering properly, magnesium builds up in the bloodstream.
Over-supplementation: Excessive use of magnesium-containing antacids or laxatives (like Milk of Magnesia), especially in patients with reduced kidney function.
Treatment focuses on restoring balance while protecting the heart and nervous system.
For Low Magnesium: If the deficiency is mild, oral supplements (like magnesium citrate) are used. In severe cases, Magnesium Sulphate is given via an IV drip.
For High Magnesium: The first step is stopping any magnesium intake. If the heart is affected, IV Calcium is administered—calcium acts as a direct “antidote” to the effects of too much magnesium.
Magnesium Blood Test – Overview (MedlinePlus)
Hypomagnesemia: Low Magnesium Causes & Symptoms (MSD Manuals)
Hypermagnesemia: High Magnesium Causes & Management (StatPearls/NIH)
Magnesium Health Professional Fact Sheet (National Institutes of Health)
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