What magnesium supplement is recommended?

Recommended Magnesium Supplement

For general supplementation, organic magnesium salts (magnesium citrate, aspartate, or lactate) are recommended over magnesium oxide due to superior bioavailability, though magnesium oxide remains appropriate for constipation or when higher elemental magnesium content is needed. 1

Formulation Selection by Clinical Context

For General Magnesium Supplementation or Deficiency

Organic magnesium salts are the preferred choice:

• Magnesium citrate, aspartate, or lactate have significantly higher bioavailability than magnesium oxide or hydroxide 1, 2, 3
• These organic forms are better absorbed throughout the gastrointestinal tract and cause fewer gastrointestinal side effects 1
• Start with the recommended daily allowance: 320 mg elemental magnesium for women, 420 mg for men 4
• Liquid or dissolvable magnesium products are generally better tolerated than pills 4

For Chronic Constipation

Magnesium oxide is specifically recommended:

• The American Gastroenterological Association conditionally recommends magnesium oxide for chronic idiopathic constipation 4
• Start with 400-500 mg daily and titrate based on symptom response 4
• The osmotic effect that causes diarrhea with magnesium oxide is actually therapeutic in this context 4
• Avoid in patients with creatinine clearance <20 mL/min due to hypermagnesemia risk 4

For Bartter Syndrome or Tubular Disorders

Organic magnesium salts are strongly recommended:

• Use magnesium aspartate, citrate, or lactate specifically due to superior bioavailability 1
• Target plasma magnesium level >0.6 mmol/L 1, 2
• Spread doses throughout the day to maintain stable levels 1

For Short Bowel Syndrome or Malabsorption

Magnesium oxide is the initial choice, with specific administration timing:

• Use 12-24 mmol daily (approximately 480-960 mg elemental magnesium) 4, 2
• Administer at night when intestinal transit is slowest to maximize absorption 4, 2, 3
• First correct water and sodium depletion with IV saline to address secondary hyperaldosteronism before supplementing magnesium 4, 2, 3
• If oral supplementation fails, consider IV or subcutaneous magnesium sulfate 4, 3

Dosing Algorithm

Step 1: Assess Renal Function

• Check creatinine clearance before initiating any magnesium supplementation 4
• Absolute contraindication if creatinine clearance <20 mL/min 4

Step 2: Identify Clinical Context

• For general supplementation or mild deficiency: organic salts (citrate, aspartate, lactate) 1, 2
• For constipation: magnesium oxide 4
• For malabsorption syndromes: magnesium oxide given at night 4, 2, 3

Step 3: Initiate Appropriate Dose

• General supplementation: 320 mg (women) or 420 mg (men) elemental magnesium daily 4
• Constipation: 400-500 mg magnesium oxide daily 4
• Deficiency states: 12-24 mmol daily (480-960 mg elemental magnesium) 4, 2

Step 4: Divide Doses Throughout Day

• Spread supplementation into multiple doses to maintain stable serum levels and improve tolerance 1, 3
• Exception: malabsorption patients should take at night 4, 2, 3

Step 5: Monitor Response

• Check magnesium levels 2-3 weeks after starting supplementation 4
• Reassess every 3 months once on stable dose 4
• Monitor for diarrhea, abdominal distension, and gastrointestinal intolerance 4

Important Caveats

Bioavailability differences are clinically significant:

• Magnesium oxide contains more elemental magnesium per tablet (60% elemental content) but has poor absorption 5
• Organic salts have lower elemental magnesium content but superior absorption 1, 2
• The net bioavailable magnesium may be similar, but organic salts cause fewer GI side effects 1

Common pitfall to avoid:

• Do not attempt magnesium supplementation in volume-depleted patients without first correcting sodium and water status with IV saline 4, 2, 3
• Secondary hyperaldosteronism from volume depletion causes renal magnesium wasting that will negate oral supplementation 4

Hypokalemia consideration:

• Hypomagnesemia causes refractory hypokalemia that will not respond to potassium supplementation until magnesium is corrected 4
• Always check and correct magnesium when treating persistent hypokalemia 4