Relationship of total water intake and specific components of water intake to hydration measures: National Health and Nutrition Examination Survey (NHANES) 2001–2010

Abstract

NHANES data were used to assess the relationship of usual intake of total water, water from food, fluid intake, and specifically water in the diets of those 19+ years of age to hydration measures: plasma osmolality (Posm), urine osmolality (Uosm) and specific gravity (USG). Intake was determined using the National Cancer Institute method and quartiles of intake were determined. Covariate adjusted regression analyses were used to assess p‐for‐trend of intake variables to hydration measures. Posm (N=22,662) was inversely (p<0.001) related to total water, fluid and water intake; Posm decreased 0.36 ± 0.05 mmol/kg, 0.32 ± 0.05 and 0.24 ± 0.05 mmol/kg for each quartile increase in total water, fluid and water intake respectively. Food moisture was not related to Posm. Uosm (N=5,126) and USG (N=4,615) measured on a spot urine collection were inversely (p<0.001) related to total water, fluid and water intake. For each quartile increase in total water intake, fluid intake and water intake, Uosm decreased 41.8 ± 6.1, 40.7 ± 5.9 and 31.2 ± 5.7 mOsm/kg, respectively and USG decreased 0.0010 ± 0.0002, 0.0009 ± 0.0002 and 0.0007 ± 0.0002, respectively. Food moisture was modestly related to Uosm (−12.9 ± 3.9; p=0.0015) and USG (−0.0003 ± 0.0001; p=0.0118). Given the physiological range of variation of Posm, Uosm and USG, Uosm appears to be the most sensitive marker of total water intake and best measure of hydration in the general population. Support: Danone Research.