Racial Differences in 24 Hour Urinary Hydration Markers

Abstract

Prior literature has investigated racial/ethnic differences in hydration status based on spot urine samples, however, no literature has examined these differences using 24 h urinary hydration measures. PURPOSE: To examine 24 h urinary hydration markers in college-aged non-Hispanic White (WH) and non-Hispanic Black (BL) men and women. METHODS: Thirteen men (BL, n=6; WH, n=7) and nineteen women (BL, n=16, WH, n=3) (mean±SD; age, 20±4y; height, 169.2±12.2cm; body mass, 71.3±12.2kg; body fat, 20.8±9.7%), combined from two separate research projects were included. Participants provided a 24 h urine sample across 7 (n=13) or 3 (n=19) consecutive days (148 d total) for assessment of urine volume (UVOL), urine osmolality (UOSM), urine specific gravity (USG), and urine color (UCOL). Differences in 24 h hydration status between sex and ethnicity were assessed using linear mixed effects models with associated Bonferroni post hoc analyses. Significance was set a-priori at p<0.05. RESULTS: UVOL was significantly lower in BL (0.85±0.43 L) compared to WH college students (2.03±0.70 L) (p<0.001). Conversely measures of UOSM, USG, and UCOL, were significantly greater in BL (716±263 mOsm•kg-1, 1.020±0.007, and 4.2±1.4, respectively) compared to WH college students (473±194 mOsm•kg-1, 1.013±0.006, 3.0±1.2, and respectively) (p<0.05). Independent of race, women were significantly less hydrated than men by measures of UVOL(MD [95% CI];.-0.56 L [-0.823, -0.308], p<0.001), UOSM(107 mOsm•kg-1 [24, 190], p=0.012), USG(0.003 [0.001, 0.005], p=0.017), and UCOL(-0.6 [-1.2, -0.1], p=0.012). CONCLUSIONS: Based on 24 h urinary hydration markers, college-aged non-Hispanic Black men and women were inadequately hydrated compared to their non-Hispanic White counterparts when assessed over consecutive days. Furthermore, women were significantly less hydrated than men, independent of racial background. Given the importance of hydration on acute and long-term health, identifying populations that are inadequately hydrated may allow for the development of targeted strategies to improve habitual fluid intake. Future research examining 24 h hydration status coupled with fluid intake behaviors across a broader sample of races or ethnicities is warranted to further understand the determinants that guide drinking behaviors.