Age-related differences in water and sodium handling following 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 (CH2 O) clearance would underlie greater beverage retention in older compared to 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 5 visits, 12 young (23±3y, 7M/5F) and 12 older (67±6y, 5M/7F) subjects consumed 1 L of distilled water or beverages with 6% CHO, 0.46 g/L Na+ (GAT), 2.5% CHO, 0.74 g/L Na+ (PED), 5 AA, 1.04 g/L Na+ (ENT-5), or 8 AA, 1.38 g/L Na+ (ENT-8) over 30 min. Blood and urine were collected every hour for 4h post-ingestion; retention, CH2 O, and CNa+ were calculated at 2h and 4h. Additional calculations adjusted CH2 O and CNa+ for estimated GFR (eGFR). Water yielded the lowest retention in both groups ( p≤0.02). Retention was higher in older vs. young except in ENT-8 at 4h ( p=0.73). CH2 O was higher for older vs. young in GAT 2h ( p<0.01), and GAT and PED 4h ( p<0.01), post-ingestion, but was otherwise similar between groups. CNa+ was lower in older vs. young except in ENT-8 ( p≥0.19). Adjusting for eGFR resulted in higher CH2 O for all beverages in older vs. young ( p<0.05), but did not influence CNa+ . Older adults may better retain beverages with less Na+ than young adults due to reduced CNa+ . AA- and CHO-based, electrolyte-rich beverages may similarly promote beverage retention.