HYDRATION BIOMARKERS AS PREDICTORS OF CHANGE IN BODY WATER STATUS

Ainsley E. Huffman, Evan C. Johnson, Mikell L. Hammer, Thomas Vidal, LynnDee Summers & Stavros A. Kavouras, FACSM Human Performance Laboratory, Department of Health, Human Performance and Recreation, University of Arkansas, Fayetteville, Arkansas Changes in body water status can be measured by change in body weight and changes in blood or urine concentration. Active dehydration drives urine and blood concentration to shift in parallel. However, the relationship between these two variables may differ during normal daily living when active dehydration is not occurring. PURPOSE: The purpose of this research was to define the relationship between plasma and urine osmolality (POsmo, UOsmo, respectively) and to compare the accuracy of plasma osmolality in predicting hypohydration (urine osmolality \u3e700mosm) as an indicator of body water status. METHODS: Forty-three healthy, but not athletic (week) adults (22 males, 21 females; age, 31.8±10.9 y; height, 1.71±0.08 m; body mass, 74.4±18.5 kg; body fat, 28.1±11.6%) provided morning urine samples, recorded body mass and provided blood samples on two separate occasions a week apart. The urine and plasma osmolality of the samples as well as the recorded body masses from two visits were evaluated by linear regression and receiver operator characteristic (ROC) analysis to determine predictive accuracy of hypohydration based on urine osmolality (≥700 mmolkg-1). RESULTS: Urine osmolality was weakly related to plasma osmolality on the second visit (F[1,41] = 4.716, p=0.038, R2=0.103), but not during the first (F[1,41] = 0.015, p=0.905, R2st visit (cut off point 289 mmolkg-1, sensitivity: 0.33, and specificity: 0.84), and 64% on second visit (cut-off point: 287mmolkg-1, sensitivity: 0.638, and specificity: 0.65). CONCLUSIONS: Plasma osmolality was weakly related to urine osmolality, while plasma osmolality had limited diagnostic ability of detecting hypohydration in free-living non-athletic individuals. Future research should seek to continue to identify markers related to sub-optimal hydration state outside of athletics