Urinary calcium losses during high‐impact and resistance exercise training

Abstract

Mechanisms responsible for exercise‐induced bone mineralization and potential effects of activity on dietary calcium requirements are not completely understood. We investigated the effects of a high‐impact and resistance training exercise program versus a period of restricted physical activity on urinary calcium excretion. Ten healthy, moderately active, men (27.0 ± 5.8 years) participated in a 3‐week randomized, cross‐over study. Subjects were assigned to complete 7‐day periods of a) daily exercise (EX) including high‐impact and resistance training activities and b) exercise restriction with a one‐week washout period between trials. During both phases, subjects consumed four, 8‐ounce servings of low‐fat (1%) milk daily and avoided other dietary and supplemental sources of calcium. Urine was collected throughout the final 72 hours of each study phase. Urinary calcium and sodium excretions (mean ± SEM) were 14.7 ± 5.2 % and 15.8 ± 3.0 % lower (P<0.05), respectively, during the EX phase. This occurred despite subjects consuming more (~300 mg/d; P<0.05) sodium during the EX phase. These data suggest that healthy, moderately active men excrete significantly less urinary calcium during a period of exercise training versus inactivity. Therefore, renal conservation of calcium may be partially responsible for improved bone mineralization that has been observed during periods of greater physical activity.