Multicompartmental analysis of magnesium and calcium kinetics during growth: relationships with body composition

Stable isotope techniques permit a unique approach to the assessment of magnesium metabolism, including absorption, excretion, pool sizes, and turnover. Findings from our recent studies on magnesium and calcium kinetics indicate close relationships between the mass of the magnesium exchangeable pool, efflux from this pool, and body weight. In this report, we further evaluate these data by relating the kinetic values with other measures of body composition. We found that fat-free mass represents the single body composition parameter that most closely correlates with magnesium kinetic data. Body composition has a stronger relationship with magnesium kinetics than with calcium kinetics. These relationships provide justification for basing dietary magnesium requirements in children on body composition measures such as body weight or, where available, fat-free mass. Further studies to evaluate these relationships are indicated in situations where either magnesium status or body composition is abnormal.