From the Guidelines
Excessive magnesium supplementation can lead to hypermagnesemia, a condition characterized by serum magnesium concentrations >2.2 mEq/L, which can cause severe side effects.
Side Effects of Excessive Magnesium Supplementation
- Neurological symptoms: muscular weakness, paralysis, ataxia, drowsiness, and confusion 1
- Cardiovascular effects: vasodilation, hypotension, bradycardia, cardiac arrhythmias, and cardiorespiratory arrest 1
- Gastrointestinal symptoms: nausea and vomiting 1
- Electrolyte and fluid abnormalities: hypophosphatemia, hyperosmolar dehydration 1
- Respiratory depression: can occur at high serum concentrations 1
Magnesium Toxicity
Magnesium toxicity can occur at levels of 2.5–5 mmol/L, presenting with ECG interval changes, AV nodal conduction block, bradycardia, hypotension, and cardiac arrest at levels of 6–10 mmol/L 1. Patients with renal failure and metabolic derangements are at higher risk of developing toxicity after relatively lower magnesium doses 1.
Prevention and Treatment
Empirical calcium administration may be lifesaving in cases of magnesium toxicity 1. Monitoring of serum magnesium levels and electrocardiographic monitoring can help prevent and intervene in lethal cardiac rhythms 1.
The FDA Drug Labels for magnesium (PO) do not address this question.
From the Research
Side Effects of Excessive Magnesium Supplementation
- Excessive ingestion of magnesium may lead to hypermagnesemia even without kidney dysfunction, as reported in a case study 2.
- Overdose of magnesium hydroxide can induce diarrhea, which is followed by excessive magnesium loss, and may lead to paradoxical hypomagnesemia 2.
- Long-term excessive magnesium supplementation has been shown to be deleterious for bones in rats, with significant reductions in bone volume, density, and strength 3.
- High levels of magnesium supplementation may also lead to an increase in urinary excretion of magnesium, without significant changes in serum magnesium levels 4.
- Potential adverse effects of magnesium overload have been raised in major trials of supplementation with magnesium, although the exact nature of these effects is not fully understood 5.
Potential Health Risks
- Excessive magnesium supplementation may lead to cardiovascular problems, as magnesium plays a key role in modulating neuronal excitation, intracardiac conduction, and myocardial contraction 5.
- High levels of magnesium may also affect vascular tone, atherogenesis, and thrombosis, which can increase the risk of cardiovascular disease 5.
- Additionally, excessive magnesium supplementation may lead to changes in bone mineral density and vascular calcification, although the exact effects are not fully understood 4, 3.