Best Magnesium Form for Absorption
Magnesium citrate demonstrates superior bioavailability compared to other magnesium formulations, with the highest serum magnesium concentrations after both acute and chronic supplementation.
Evidence-Based Ranking of Magnesium Forms
Highest Bioavailability
- Magnesium citrate shows the greatest mean serum magnesium concentration following both acute (P = 0.026) and chronic (P = 0.006) supplementation compared to other forms 1
- Organic magnesium salts (citrate, aspartate, lactate) have higher bioavailability than inorganic compounds like magnesium oxide or hydroxide 2, 3
- Magnesium citrate led to superior absorption at 60 days (P = 0.033) and the highest salivary magnesium concentration (P = 0.027) compared to all other treatments 1
Moderate Bioavailability
- Magnesium glycinate (amino acid chelate) shows greater absorption than magnesium oxide but less than citrate 1
- Magnesium acetyl taurate specifically increases brain magnesium levels in animal studies, suggesting tissue-specific benefits 4
- Magnesium malate (organic acid-bound) has better absorption than inorganic forms 4
Lowest Bioavailability
- Magnesium oxide resulted in no differences compared to placebo in bioavailability studies 1
- Despite containing more elemental magnesium per dose, magnesium oxide is poorly absorbed and primarily works through osmotic effects in the GI tract rather than systemic absorption 5
Clinical Context Matters
For Systemic Magnesium Repletion
- Use magnesium citrate at 12-24 mmol daily as first-line therapy for mild hypomagnesemia 2, 3
- Intestinal absorption of magnesium is typically 35-50%, making the choice of highly bioavailable forms critical 5
- Dividing doses throughout the day may improve absorption, though high single doses divided into multiple administrations did not significantly increase tissue levels in animal studies 4
For Constipation Management
- Magnesium oxide is the recommended form specifically for constipation, as its poor absorption creates the desired osmotic effect in the GI lumen 5
- The 2023 AGA/ACG guidelines recommend magnesium oxide 1.5 g/day for chronic idiopathic constipation, though lower doses of 500 mg-1 g/day are commonly used in practice 5
Important Dosing Considerations
- Timing: Administering magnesium at night when intestinal transit is slowest can maximize absorption 2
- Dose-response: The relative magnesium uptake is higher with multiple low doses throughout the day compared to a single large intake 6
- Renal function: Avoid magnesium supplementation in patients with creatinine clearance <20 mg/dL due to hypermagnesemia risk 5
Common Pitfalls to Avoid
- Don't assume elemental magnesium content equals bioavailability - magnesium oxide contains the most elemental magnesium but has the poorest absorption 5, 1
- Most magnesium salts are poorly absorbed and may worsen diarrhea in patients with GI disorders 2, 3
- Reducing excess dietary lipids can help improve magnesium absorption 2
- Monitor for secondary electrolyte abnormalities, particularly potassium and calcium, which often accompany hypomagnesemia 3
When Oral Therapy Fails
- Consider IV magnesium sulfate for severe deficiency (<1.2 mEq/L) or symptomatic patients 2, 3
- For cardiac arrhythmias associated with hypomagnesemia, administer 1-2 g IV magnesium bolus regardless of measured serum levels 2, 3
- Oral 1-alpha hydroxy-cholecalciferol in gradually increasing doses can improve magnesium balance in refractory cases, though serum calcium must be monitored regularly 2, 3