Total water intake guidelines are sufficient for optimal hydration in United States adults.

Abstract

Recent studies suggest that 24-h urine osmolality (UOsm) for optimal water intake should be maintained < 500mmol·kg-1. The purpose of this study was to determine the total water intake (TWI) requirement for healthy adults to maintain optimal hydration as indicated by 24-h urine osmolality < 500mmol·kg-1. Twenty-four-hour UOsm was assessed in 49 men and 50 women residing in the United States (age: 41 ± 14 y, body mass index: 26.3 ± 5.2kg·m-2). TWI was assessed from 7-day water turnover, using a dilution of deuterium oxide, corrected for metabolic water production. The diagnostic accuracy of TWI to identify UOsm < 500mmol·kg-1 was evaluated using receiver operating characteristic (ROC) analysis in men and women separately. Twenty-four-hour UOsm was 482 ± 229 and 346 ± 182mmol·kg-1 and TWI was 3.57 ± 1.10L·d-1 and 3.20 ± 1.27L·d-1 in men and women, respectively. ROC analysis for TWI detecting 24-h UOsm < 500mmol·kg-1 in men yielded an area under the curve (AUC) of 77.4% with sensitivity, specificity, and threshold values of 83.3%, 64.5%, and 3.39L·d-1, respectively. The AUC was 82.4% in women with sensitivity, specificity, and threshold values of 85.7%, 72.1%, and 2.61L·d-1. Considering threshold values in men and women of 3.4L·d-1 and 2.6L·d-1, respectively, maintaining TWI in line with National Academy of Medicine guidelines of 3.7L·d-1 in men and 2.7L·d-1 in women should be sufficient for most individuals in the United States to maintain 24-h UOsm < 500mmol·kg-1.