Intracellular magnesium — far more sensitive to deficiency than serum magnesium, which the body defends aggressively.
Serum magnesium is tightly regulated — the body will cannibalize bone and intracellular stores to keep serum in range. This is why most people with real magnesium deficiency have normal serum levels. RBC magnesium reflects intracellular status and catches deficiency far earlier.
Magnesium is a cofactor in 300+ enzymatic reactions, including ATP synthesis, insulin signaling, and muscle contraction. Insufficient magnesium correlates with cramps, poor sleep, arrhythmia susceptibility, and insulin resistance.
RBC magnesium is influenced by: dietary intake (dark leafy greens, nuts, seeds), GI absorption (alcohol, PPIs, and chronic diarrhea all reduce it), renal wasting (diuretics, some diabetes drugs), and supplementation (glycinate, malate, citrate are well absorbed; oxide is poorly absorbed).
Useful baseline marker for anyone with cramps, sleep issues, or metabolic syndrome. Retest 3 months after supplementation change. Oral magnesium supplementation at 300–400 mg elemental daily (glycinate or malate) is well tolerated.
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Start tracking →Informational only — not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.