Sodium Loading, Treadmill Walking and the Acute Redistribution of Bone Mineral Content on Dual Energy X-ray Absorptiometry Scans
American Journal of Physiology. Regulatory Integrative and Comparative Physiology
To assess relationships between plasma sodium concentration ([Na+]) and bone mineral content (BMC) after an acute sodium load plus treadmill walking and quantify the amount of sodium the dual energy x-ray absorptiometry (DXA) scan could detect. The primary study was a single-blind randomized control crossover trial under two Conditions: ingestion of six flour tablets (P: placebo trial) or six 1g-NaCl tablets (S: salt intervention trial). Tablets were ingested after baseline blood and urine
... ction followed immediately by the DXA scan. After 60 minutes of rest, a 45-minute treadmill walk was conducted. Immediately post-exercise, blood and urine collected and the DXA scan repeated. Main outcomes included changes (∆: post minus pre) in plasma [Na+] and BMC. Additionally, six 1g-NaCl tablets were superimposed over a DXA spine phantom for separate quantification of sodium as BMC. 14 subjects completed the primary study. Two-way repeated-measures ANOVA tests revealed significant Interaction (F=13.06;p=0.0007), Condition (F=21.88;p<0.001) and Time (F=6.51;p=0.014) effects in plasma [Na+]. Significant Condition (F=6.46;p=0.014) effect also noted in urine [Na+]. Total body BMC∆ negatively correlated with plasma [Na+]∆ (r=-0.43;p=0.02) and urine [Na+]∆ (r=-0.47;p=0.01). Total body BMC∆ in the S trial (-5.5±27g) closely approximated the amount of NaCl ingested and subsequently absorbed into the bloodstream. The DXA scan quantified 67% of NaCl tablets as BMC, in spine phantom analyses. Total body BMC∆ negatively related to plasma and urine [Na+]∆ after treadmill walking. Reductions in total body BMC closely approximated the amount of NaCl ingested (~6g). The DXA scan quantified NaCl as BMC.