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.
Purpose
To investigate age‐related differences in fluid retention and free water (CH 2 O) 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 CH 2 O 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.
Methods
Over 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, CH 2 O, and CNa ⁺ were calculated at each time point. Additional calculations were made to adjust CH 2 O and CNa ⁺ for estimated GFR (eGFR).
Results
Fluid 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. CH 2 O 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 CH 2 O for all beverages in O vs. Y ( p <0.05), but had no effect on CNa ⁺ or within‐group observations.
Conclusions
Beverages with higher Na ⁺ concentrations resulted in reduced CH 2 O 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 Information
Entrinsic Health Solutions, Inc; NIH T32 Grant #5T32AG049676‐03
This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .