Age-related differences in water and sodium handling after commercial hydration beverage ingestion

Aging is associated with altered water, electrolyte, and glucose handling. Alternative beverages to those containing carbohydrate (CHO) should be considered for older adults. We hypothesized that reduced sodium (CNa⁺) and/or water (CH₂O) clearance would underlie greater beverage retention in older compared with young adults, secondary to reduced glomerular filtration rate (GFR). We further hypothesized that amino acid (AA)- and CHO-based beverages would promote retention better than water. Over five visits, 12 young (23 ± 3 yr; 7 men, 5 women) and 12 older (67 ± 6 yr; 5 men, 7 women) subjects consumed 1 liter of distilled water or beverages with 6% CHO, 0.46 g/l Na⁺ [Gatorade (GAT)]; 2.5% CHO, 0.74 g/l Na⁺ [Pedialyte (PED)]; 5 AA, 1.04 g/l Na⁺ [enterade (ENT)-5]; or 8 AA, 1.38 g/l Na⁺ (ENT-8) over 30 min. Blood and urine were collected every hour for 4 h after ingestion; retention, CH₂O, and CNa⁺ were calculated at 2 and 4 h. Additional calculations adjusted CH₂O and CNa⁺ for estimated GFR (eGFR). Water yielded the lowest retention in both groups ( P ≤ 0.02). Retention was higher in older vs. young adults except for ENT-8 at 4 h ( P = 0.73). CH₂O was higher for older vs. young adults for GAT at 2 h ( P < 0.01) and GAT and PED at 4 h ( P < 0.01) after ingestion but was otherwise similar between groups. CNa⁺ was lower in older vs. young adults except for ENT-8 ( P ≥ 0.19). Adjusting for eGFR resulted in higher CH₂O for all beverages in older vs. young adults ( P < 0.05) but did not influence CNa⁺. Older adults may better retain beverages with less Na⁺ than young adults because of reduced CNa⁺. AA- and CHO-based electrolyte-rich beverages may similarly promote beverage retention. NEW & NOTEWORTHY Commercially available amino acid (AA)-containing beverages may provide an alternative to traditional carbohydrate (CHO)-containing beverages, particularly for older adults with attenuated water, electrolyte, and glucose handling. We compared beverage retention and free water and sodium clearance between young and older adults after ingestion of water, two CHO-based beverages, and two AA-based beverages. Our data suggest that older adults better retain beverages with less sodium compared with young adults and that AA-based and CHO-based electrolyte-containing beverages similarly promote retention.