Effect of Dietary Sodium on Fluid/Electrolyte Regulation During Bed Rest
Document Type
Article
Publication Date
1-1-2003
Description
Background: A negative fluid balance during bed rest (BR) is accompanied by decreased plasma volume (PV) which contributes to cardiovascular deconditioning. Hypothesis: We hypothesized that increasing dietary sodium while controlling fluid intake would increase plasma osmolality (POSM), stimulate fluid conserving hormones, and reduce fluid/electrolyte (F/E) losses during BR; conversely, decreasing dietary sodium would decrease POSM, suppress fluid conserving hormones, and increase F/E losses. Methods: We controlled fluid intake (30 ml · kg-1 · d-1) in 17 men who consumed either a 4.0 ± 0.06 g · d-1 (174 mmol · d-1) (CONT; n = 6), 1.0 ± 0.02 g · d-1 (43 mmol · d-1) (LS; n = 6), or 10.0 ± 0.04 g · d-1 (430 mmol · d-1) (HS; n = 5) sodium diet before, during, and after 21 d of 6° head-down BR. PV, total body water, urine volume and osmolality, POSM, and F/E controlling hormone concentrations were measured. Results: In HS subjects, plasma renin activity (-92%), plasma/urinary aldosterone (-59%; -64%), and PV (-15.0%; 6.0 ml · kg-1; p < 0.05) decreased while plasma atrial natriuretic peptide (+34%) and urine antidiuretic hormone (+24%) increased during BR (p < 0.05) compared with CONT. In LS, plasma renin activity (+166%), plasma aldosterone (+167%), plasma antidiuretic hormone (+19%), and urinary aldosterone (+335%) increased with no change in PV compared with CONT (p < 0.05). Total body water did not change in any of the subjects. Conclusions: Contrary to our hypothesis, increasing dietary sodium while controlling fluid intake during BR resulted in a greater loss of PV compared with the CONT subjects. Reducing dietary sodium while controlling fluid intake did not alter the PV response during BR compared with CONT subjects.
Citation Information
Williams, W. Jon; Schneider, Suzanne M.; Gretebeck, Randall J.; Lane, Helen W.; Stuart, Charles A.; and Whitson, Peggy A.. 2003. Effect of Dietary Sodium on Fluid/Electrolyte Regulation During Bed Rest. Aviation Space and Environmental Medicine. Vol.74(1). 37-46. https://pubmed.ncbi.nlm.nih.gov/12546297/ PMID: 12546297 ISSN: 0095-6562