Timing of Calcium Supplementation Relative to Exercise Alters the Calcium Homeostatic Response to Vigorous Exercise

Presentation Number: OR43-6
Date of Presentation: June 18th, 2013

Vanessa D Sherk*1, Daniel W Barry1, Karen L Villalon1, Kent C Hansen2, Pamela Wolfe1 and Wendy M Kohrt1
1University of Colorado - Anschutz Medical Campus, Aurora, CO, 2Winona State University

Abstract

Larger than expected decreases in bone mineral density have been observed in road cyclists over a year of training. This may be partly mediated by calcium (Ca) losses during exercise bouts. An exercise-induced decrease in serum ionized calcium (iCa) is thought to trigger an increase in parathyroid hormone (PTH), which may stimulate bone resorption. The ingestion of a Ca-fortified beverage before and during exercise has been found to attenuate the PTH and bone resorption responses to an acute cycling bout. The purpose of this study was to determine whether taking Ca and vitamin D before versus after a vigorous bout of exercise influenced disruptions in Ca homeostasis and bone resorption in competitive male cyclists. Fifty-two men aged 18-45 yr were randomized to take a chew containing 1000 mg Ca and 1000 IU vitamin D either 30 minutes BEFORE or 1 hour AFTER a simulated 35-km cycling time trial. Patches were used for collection of sweat during exercise and dermal Ca loss was estimated. Sweat volume was assumed to be the change in body weight adjusted for fluid loss and intake. Serum iCa and PTH were measured before and immediately after exercise, and a marker of bone resorption (Collagen Type-1 C-Telopeptide; CTX) was measured before and 30 minutes after. Sweat and Ca losses were 1.41±0.22 L (mean±SD) and 89.6±34.3 mg in the BEFORE group and 1.43±0.25 L and 94.6±49.0 mg in the AFTER group.  Decreases in serum iCa occurred in both groups (BEFORE: 1.22±0.04 to 1.19±0.03; AFTER: 1.23±0.04 to 1.16±0.06; p≤0.001), but decreases were greater (p=0.03) in the AFTER group. There was a trend for Ca before exercise to attenuate the increase in PTH compared to Ca after exercise (162±331% vs. 244±351%; p=0.07). There were no treatment effects on the change in CTX; both groups showed increases (p<0.05) after the time trial (BEFORE: 50±91%; AFTER: 50±101%). Ca supplementation before exercise reduced, but did not prevent changes in iCa and PTH during exercise. Further studies are needed to determine whether the magnitude of bone resorption response is indicative of acute serum Ca needs during and after exercise that are unmet by Ca availability in the gut.

 

Nothing to Disclose: VDS, DWB, KLV, KCH, PW, WMK