Why Magnesium Matters

Magnesium is involved in over 300 enzymatic reactions in the body. It helps muscles contract and relax, keeps your heartbeat steady, supports nerve transmission, and is part of how your bones store calcium. The kidneys are the regulator: extra magnesium gets filtered out and excreted in urine, which is why magnesium levels stay stable in healthy adults even if intake varies.

Most Canadians get magnesium from food: pumpkin seeds, almonds, spinach, black beans, dark chocolate, and whole grains. Supplements (magnesium glycinate, citrate, oxide) are common and usually safe at the recommended dose. The problem starts when intake outpaces the kidneys' ability to clear it.

What Counts as Hypermagnesemia

Normal serum magnesium runs 0.7 to 1.0 mmol/L (about 1.7 to 2.2 mg/dL). Anything above that is hypermagnesemia, though symptoms usually don't appear until levels exceed 2.0 mmol/L (4.9 mg/dL). Severe symptoms typically need levels above 3.0 mmol/L.

The usual causes:

• Kidney disease. By far the most common cause. If your eGFR is below 30, the kidneys can't clear magnesium fast enough, and even modest supplement use can push levels up.
• Magnesium-containing medications. Maalox, Mylanta, milk of magnesia, magnesium-based laxatives. Long-term high-dose use, especially in older adults with declining kidney function, is a classic setup.
• IV magnesium in hospital. Used to treat preeclampsia and certain heart rhythm problems. Closely monitored, but levels can climb fast.
• Supplement overuse. Less common, but possible with very high oral doses (multiple grams per day) on top of a magnesium-rich diet.

Higher risk groups include people with chronic kidney disease, older adults taking multiple medications, hypothyroidism, adrenal insufficiency, and anyone on lithium.

Symptoms by Severity

Symptoms scale with the magnesium level:

Mild (2.0 to 3.0 mmol/L): Nausea, flushing, headache, drowsiness, mild muscle weakness.

Moderate (3.0 to 5.0 mmol/L): Slow heart rate (bradycardia), low blood pressure, deep tendon reflexes disappearing, more pronounced weakness, mental fog.

Severe (above 5.0 mmol/L): Respiratory depression, complete loss of reflexes, cardiac arrest. This is a medical emergency.

If you're on a magnesium-containing antacid or laxative and you start feeling unusually sleepy or weak, or your face suddenly feels warm and flushed, that's worth calling about, especially if you have kidney trouble. Symptoms can creep up gradually and easily get blamed on something else.

How It's Diagnosed

A single blood test measures serum magnesium. If it's elevated, your doctor will usually run:

• Creatinine and eGFR (kidney function)
• Electrolytes (sodium, potassium, calcium, phosphate)
• ECG if the level is significantly high, since severe hypermagnesemia changes the heart's electrical pattern

The medication list is just as important as the lab work. Long-term laxative or antacid use is often the cause, but only if someone thinks to ask.

Treatment

Mild cases usually just need the source removed: stop the supplement, switch to a non-magnesium antacid (calcium carbonate works), and the kidneys do the rest within a day or two.

Moderate cases may need IV fluids to flush magnesium through the kidneys, plus IV calcium gluconate, which is a fast antidote that counteracts magnesium's effect on the heart and muscles.

Severe cases or patients with kidney failure may need hemodialysis, which clears magnesium quickly and reliably.

Prevention is straightforward if you're high risk: check labels (a surprising number of OTC heartburn and constipation products contain magnesium), don't stack supplements with magnesium-containing medications, and let your pharmacist know about every supplement you take.

The Bottom Line

Hypermagnesemia is rare in healthy people but very real if you have reduced kidney function or take magnesium-containing OTC medications regularly. Early signs (flushing, drowsiness, mild weakness) are easy to miss, and severe cases can be life-threatening. If you have CKD or you're using magnesium-based laxatives or antacids long term, ask your doctor to check a magnesium level at your next visit.

FAQ Section

1. How much magnesium should adults get daily?
   The RDA is 400 to 420 mg for adult men and 310 to 320 mg for adult women. Pregnancy needs are slightly higher.
2. Can you get too much from food alone?
   Almost never. Healthy kidneys excrete the excess. The problem is supplements and magnesium-based OTC medications, not diet.
3. What are the risks of magnesium supplements?
   For healthy people, the main risk is loose stools at higher doses. For people with kidney disease, even modest doses can push levels into the toxic range.
4. How do I know if my magnesium is high?
   The only reliable way is a blood test. Symptoms like weakness or flushing can suggest it, but they're not specific.
5. Is hypermagnesemia common?
   Uncommon in healthy adults, more common in patients with CKD, on dialysis, or using magnesium-containing antacids and laxatives long term.
6. What other conditions does it affect?
   High magnesium can slow the heart, lower blood pressure, blunt muscle reflexes, and at very high levels stop breathing.
7. When should I get to a doctor?
   Anytime you have severe weakness, slow or irregular heartbeat, shortness of breath, or confusion, particularly if you're on magnesium-containing medications or have known kidney disease. Don't wait it out.

Disclaimer: This blog post is intended for educational purposes only and should not be taken as medical advice. Always consult your healthcare provider for personal health concerns.