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

Abstract

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.