Why Magnesium Deficiency Is Often Missed
Serum Magnesium Is Unreliable
Only 1% of body magnesium is in the blood. Serum levels can be normal even when intracellular and total body stores are severely depleted. A 24-hour urine magnesium or magnesium retention test is more sensitive in symptomatic patients.
Causes of Low Magnesium
| Cause | Mechanism |
|---|---|
| PPIs (omeprazole, lansoprazole) | Impair intestinal magnesium transport — especially with long-term use |
| Diuretics (loop & thiazide) | Increase renal magnesium excretion |
| Alcohol excess | Increased renal loss; poor dietary intake |
| Diarrhoea / malabsorption | GI loss — Crohn's, coeliac, short bowel |
| Type 2 diabetes | Increased renal excretion; osmotic diuresis |
| Digoxin / aminoglycosides | Drug-induced renal magnesium wasting |
Consequences of Deficiency
- Cardiac arrhythmias — magnesium stabilises cardiac ion channels; hypomagnesaemia predisposes to AF, VT, and Torsades de Pointes
- Hypokalaemia — magnesium is required for potassium retention; you cannot correct potassium without correcting magnesium
- Hypocalcaemia — magnesium is required for PTH secretion
- Muscle cramps, weakness, fatigue
- Migraine — low magnesium associated with migraine frequency
- Insulin resistance and type 2 diabetes
Correct Magnesium FirstIn patients with both hypokalaemia and hypomagnesaemia, potassium levels will not correct until magnesium is replaced. Always check magnesium when treating low potassium.
What are symptoms of low magnesium?
Muscle cramps and twitching, fatigue, irritability, insomnia, irregular heartbeat, anxiety, and numbness/tingling. Often non-specific and attributed to other causes.
How is magnesium deficiency treated?
Mild deficiency: oral magnesium supplements (glycinate or citrate forms are better absorbed than oxide). Severe or symptomatic deficiency: IV magnesium sulphate.
Does magnesium help with migraines?
Evidence supports magnesium supplementation (400 mg/day magnesium oxide or citrate) for migraine prevention. Intravenous magnesium is also used to treat acute migraine in emergency settings.
Can high magnesium be dangerous?
Yes — hypermagnesaemia is almost always due to over-supplementation or renal failure. Symptoms: nausea, low BP, respiratory depression, cardiac arrest at very high levels. Treat with IV calcium and supportive care.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.