A randomized trial to assess beverage hydration index in healthy older adults

Abstract

Background: The beverage hydration index (BHI) is a composite measure of fluid balance after consuming a test beverage relative to water. BHI is a relatively new measure that has been explored in young, but not yet older, adults.

Objective: The aim of this study was to investigate potential differences in BHI between euhydrated younger and older adults after drinking 4 different commercial beverages. We hypothesized that 1) older subjects would remain in positive fluid balance longer than young subjects after ingestion of each test beverage due to decreased urinary excretion rates, 2) glucose (glu)- and amino acid (AA)-based hydration beverages with sodium would have a BHI greater than water in both groups, and 3) the traditional 2-h postingestion BHI may be inappropriate for older adults.

Methods: On 5 separate visits, 12 young (23 ± 3 yr, 7 M/5F) and 12 older (67 ± 6 yr, 5 M/7F) subjects consumed 1 L of distilled water, G-20 (6% CHO, 20 mmol/L Na+), G-45 (2.5% CHO, 45 mmol/L Na+), AA-30 (5 AAs, 30 mmol/L Na+), or AA-60 (8 AAs, 60 mmol/L Na+) over 30 min. Blood and urine samples were collected before ingestion and at 0, 60, 120, 180, and 240 min postingestion with additional venous blood sampling at 5, 10, 15, and 30 min postingestion.

Results: In young subjects, BHI increased with increasing beverage Na+ concentration, and AA-60 had the highest BHI (AA-60 = 1.24 ± 0.10 compared with water = 1.00, P = 0.01). For older subjects, BHI was highest in AA-30 (AA-30; 1.20 ± 0.13 compared with water, P < 0.01) and was still in flux beyond 2 h in AA-60 (P < 0.05).

Conclusions: Beverage Na+ content progressively increased BHI in young adults independent of glucose or AA content. For older adults, the AA-30 beverage had the highest BHI. A 4-h BHI may be more appropriate for older adults due to attenuated urine excretion rates. This trial was registered at clinicaltrials.gov as NCT03559101.

Keywords: BHI; eGFR; healthy aging; net fluid balance; plasma volume.

FIGURE 3

Relation between estimated glomerular filtration rate (eGFR) and time spent in positive fluid balance in young compared to older adults. Separate ordinary least-squares regression analyses assessed the correlation between eGFR and time in positive fluid balance in young and older adults. Older: R² = 0.47,P = 0.01; young: R² = 0.10, P = 0.38.

FIGURE 1

Cumulative (A, B) and time point (C, D) urine output and fluid balance (E, F) in young and older adults. Values are means ± SEM. Differences within and between groups were assessed by 2-way and 3-way ANOVA, respectively, with Bonferroni post hoc analyses performed to correct for multiple comparisons. ^aP < 0.05 G-20 compared to water; ^bP < 0.05 G-45 compared to water; ^cP < 0.05 AA-30 compared to water; ^dP < 0.05 AA-60 compared to water; ¹P < 0.05 water compared to young; ²P < 0.05 G-20 compared to young; ³P < 0.05 G-45 compared to young; ⁴P < 0.05 AA-30 compared to young; ⁵P < 0.05 AA-60 compared to young.

FIGURE 2

Beverage hydration index (BHI) for the 4 test beverages in young and older adults at 2 h (A, B) and 4 h (C, D). Values are means ± SEM. Differences within and between groups were assessed by 2-way and 3-way ANOVA, respectively, with Bonferroni post hoc analyses performed to correct for multiple comparisons. *P < 0.05 compared to water; †P < 0.05 compared to AA-60; ^XP < 0.05 compared to young; ‡P < 0.05 compared to 2 h.

FIGURE 4

Comparison of free water clearance (CH₂O; index of solute reabsorption) at varying urine flows (V̇; index of solute delivery) between old and young subjects. Ordinary least-squares regression analyses assessed the correlation between CH₂O and V̇ in young and older adults. Each subject is represented a total of 5 times, once for each test beverage, at the 2-h time point. Older: R² = 0.59, P < 0.01; young: R² = 0.76, P < 0.01. Neither the slope (P = 0.40) nor the intercept (P = 0.34) was different between groups.

FIGURE 5

Plasma volume changes (% baseline) across the 4 h protocol in young (A) and older (B) adults. Values are means ± SEM. Differences within and between groups were assessed by 2-way and 3-way ANOVA, respectively, with Bonferroni post hoc analyses performed to correct for multiple comparisons. Additional plasma volume measurements were made in a subgroup of subjects at 5-, 10-, and 15-min time points, with the following sample sizes. Water: young n = 6, older n = 7; G-20: young n = 3, older n = 6; G-45: young n = 5, older n = 6; AA-30: young n = 3, older n = 8; AA-60: young n = 4, older n = 4. ^aP < 0.05 G-20 compared to water; ^bP < 0.05 G-45 compared to water; ^cP < 0.05 AA-30 compared to water; ^dP < 0.05 AA-60 compared to water; ³P < 0.05 G-45 compared to young; ⁴P < 0.05 AA-30 compared to young. The inset bar graph is the mean of the 60 min to 240 min %PV change for each beverage to represent the plateau phase. *P < 0.05 compared to water. †P < 0.05 compared to water, G-20, G-45, and AA-60.