Age and Muscle Function Are More Closely Associated With Intracellular Magnesium, as Assessed by 31 P Magnetic Resonance Spectroscopy, Than With Serum Magnesium.
Level 4 - case-series / case-control
Cross-sectional observational analysis within a cohort
PubMed 31827445 · doi:10.3389/fphys.2019.01454
What was done
Researchers measured intramuscular ionized magnesium using phosphorus magnetic resonance spectroscopy (31P-MRS) and total serum magnesium in 441 participants (aged 24–98 years) from the Baltimore Longitudinal Study of Aging (BLSA). They analyzed cross-sectional associations between magnesium measures, chronological age, and knee-extension strength in men and women.
What was found
Intramuscular ionized magnesium was negatively associated with age (β = -0.29, p < 0.001, R2 = 0.08) and positively associated with knee-extension strength (women: β = 0.31, p < 0.001, R2 = 0.1; men: β = 0.2, p = 0.003, R2 = 0.04). Total serum magnesium showed no significant association with age (p = 0.27) or muscle strength (p = 0.1). Intramuscular ionized magnesium levels were significantly lower in women than in men (p < 0.001).
Why it matters
Serum magnesium reflects less than 1% of total body magnesium and may miss functional or intracellular depletion. Non-invasive 31P-MRS measurement of intramuscular magnesium may provide a more biologically relevant biomarker for investigating age-related muscle weakness and response to magnesium interventions.
Limits
The analysis is cross-sectional, so causality cannot be established. The variance explained was modest (R2 = 0.04 to 0.10 for strength), and the abstract does not report dietary magnesium intake, kidney function, medication use, or longitudinal changes.
Cited by
- supports Serum magnesium testing does not accurately reflect total body magnesium status because most magnesium resides intracellularly.