Age‐Related Differences in Water and Sodium Handling Following Commercial Hydration Beverage Ingestion

Abstract

Advancing age is associated with alterations in renal function, in particular water, electrolyte, and glucose handling. Glucose‐containing oral rehydration beverages may not be ideal choices for older adults (O) and alternative commercial hydration beverages are available.PurposeTo investigate age‐related differences in fluid retention and free water (CH2O) and sodium clearance (CNa+) after ingestion of water and 4 hydration beverages. We hypothesized that (1) fluid retention would be greater in O compared to young (Y) adults, (2) increased fluid retention in O would be mediated by reduced CNa+ and/or CH2O secondary to a reduced glomerular filtration rate (GFR), and (3) amino acid‐based beverages and glucose‐based beverages would be better than water in promoting fluid retention.MethodsOver 5 separate visits, 12 Y (23±3 yr, 7M/5F) and 12 O (67±6 yr, 5M/7F) subjects consumed 1 L of distilled water, or beverages with 6% glu, 20 mmol/L Na+ (G‐20), 2.5% glu, 45 mmol/L Na+ (G‐45), 5 AA, 30 mmol/L Na+ (AA‐30), or 8 AA, 60 mmol/L Na+ (AA‐60) over a 30 min period. Blood and urine samples were collected 2 and 4 h post‐ingestion; fluid retention, CH2O, and CNa+ were calculated at each time point. Additional calculations were made to adjust CH2O and CNa+ for estimated GFR (eGFR).ResultsFluid retention was lower in the water trial vs. all 4 other beverages at 2 (p<0.01) and 4 (p≤0.02) h post‐ingestion in both Y and O. Retention was higher in O vs. Y 2 h post‐ingestion of all 5 beverages (p<0.01), and for all beverages (p<0.01) except AA‐60 (p=0.73) at 4h. In Y, retention was higher after ingestion of AA‐60 or G‐45 (beverages with the 2 highest Na+ concentrations) vs. all other beverages at both time points (p<0.01). In O, retention was lower in AA‐60 vs. G‐20 and G‐45 (p<0.01), but not AA‐30 (p=0.06), 2 h post‐ingestion, and was similar between G‐20, G‐45, AA‐30, and AA‐60 (p>0.05) 4 h post‐ingestion. CH2O was higher in O vs. Y 2 h (p<0.01) post‐ingestion of G‐20, and 4 (p<0.01) h post‐ingestion of G‐20 and G‐45 (p<0.01). CNa+ was lower in O vs. Y 2 h after ingestion of water, G‐20, G‐45, and AA‐30 (p<0.01) and 4 h after ingestion of G‐20, G‐45, and AA‐30 (p<0.01). Adjusting for eGFR resulted in a higher CH2O for all beverages in O vs. Y (p<0.05), but had no effect on CNa+ or within‐group observations.ConclusionsBeverages with higher Na+ concentrations resulted in reduced CH2O and improved fluid retention in Y. Improved retention in O compared to Y was likely due to both a lower GFR and reduced CNa+. These results suggest that (1) older adults may be better able to retain beverages with lower Na+ loads than young adults, and (2) amino acid‐based beverages may be equally efficacious for promoting fluid retention compared to those containing glucose.Support or Funding InformationEntrinsic Health Solutions, Inc; NIH T32 Grant #5T32AG049676‐03This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.