The purpose of this study was to compare daily calcium (Ca) losses in sweat (S) and urine (U) on an exercise day (E) with losses on the preceding day (i.e., a rest day) during which no exercise (NE) was performed. Ten healthy male volunteers (23.9 ± 3.2 years) performed a single bout of moderate exercise (running at 80% HRmax) for 45 min in a warm (32 °C, 58% relative humidity) environment on E. When E and NE were compared, neither Ca intake (1,232 ± 714 and 1,148 ±482 mg, respectively) nor urinary Ca excretion (206 ± 128 and 189 ± 130 mg, respectively) were different (p > .05). Sweat Ca losses during the exercise bout averaged 45 ± 12 mg. The results indicate that, although a small amount of Ca is lost in sweat during 45 min of moderate-intensity exercise, measured (sweat and urine losses combined) Ca losses (251 ±128 and 189 ± 130 mg) were not different (p > .05) between days (E and NE, respectively). These data suggest that moderate exercise for up to 45 min in a warm, humid environment does not markedly increase Ca intake requirements.
The authors are with the University of Tennessee-Campbell Clinic: D.B. Bullen and M.L. O’Toole are with the Department of Orthopaedic Surgery, and K.C. Johnson is with the Department of Preventive Medicine. Direct correspondence to Daryll Bullen, UT Memphis Department of Orthopaedics, Coleman Building A302, Memphis, TN 38163.