Where magnesium lives
Total body magnesium distribution:
- Bone: 50-60%
- Soft tissue: ~40%
- Serum: ~1%
Why serum misleads
The body tightly regulates serum magnesium. Cells release magnesium to maintain serum levels even during cellular depletion. Serum magnesium can be normal while cellular stores are substantially depleted.
Why RBC is better
Red blood cells reflect intracellular magnesium status better than serum. RBC magnesium captures depletion that serum misses. Optimal: 5.0-6.5 mg/dL.
Deficiency symptoms
- Muscle cramps and twitches
- Sleep difficulty
- Anxiety and irritability
- Fatigue
- Headaches/migraines
- Constipation
- Heart rhythm irregularities
- High blood pressure
Supplementation
- Magnesium glycinate (best absorbed, calming)
- Magnesium citrate (absorbed; can have laxative effect)
- Magnesium malate (energy support)
- Magnesium L-threonate (brain-permeable)
- Avoid magnesium oxide (poorly absorbed)
- Typical dose: 200-400 mg daily
- Take in evening for sleep benefit
The clinical pearl: Don't trust serum magnesium alone. Order RBC magnesium for accurate cellular status. Supplementation is safe and beneficial for most adults.
Bottom line
Serum magnesium misses cellular deficiency. RBC magnesium captures it. Most adults benefit from supplementation. Glycinate or citrate are preferred forms.
~1%
total body magnesium in serum
5.0-6.5
mg/dL optimal RBC magnesium
200-400
mg typical daily supplementation