Magnesium metabolism after a full-marathon race

Abstract

Japan Journal of Physical Fitness Sports Medicine; Volume 47:221-230, 1998 Abstract: We examined the relationship between serum magnesium (sMg) change and urinary Mg (uMg) excretion, lipid metabolism, and hormonal responses induced by prolonged physical exercise. Six recreational runners voluntary participated in the study, and their sMg uMg, serum lipid, and circulatory levels of plasma hormones (ACTH, cortisol, ADH, and aldosterone) were determined during a 1-wk recovery period after a full-marathon race. Immediately after the race, fall of sMg was significant but recovered to the prerace level in the next day. Urinary Mg excretion decreased significantly after the race, and the tubular reabsorption rate (%TRMg) was elevated for 1 wk. The negative correlation between sMg and %TRMg suggested that a decreased level of sMg enhanced tubular reabsorption of Mg. On the other hand, no correlation was observed between the plasma hormone levels and %TRMg; thus, hormonal responses induced by prolonged exercise had less effect on the tubular reabsorption of Mg. Therefore, fall of sMg after the full marathon race may not be a reflection of Mg depletion but seems to be the result of a Mg shift to other regions (muscle, erythrocytes, and adipose cells) from the serum. Increased level of serum FFA after the race suggested enhanced lipolysis, which might be a cause of sMg reduction.