Associations between urinary hydration markers and metabolic dysfunction: a cross-sectional analysis of NHANES data, 2008–2010

PURPOSE: Growing evidence suggests hydration plays a role in metabolic dysfunction, however data in humans are scarce. This study examined the cross-sectional association between hydration and metabolic dysfunction in a representative sample of the US population. METHODS: Data from 3961 adult NHANES (National Health and Nutrition Examination Survey) participants (49.8% female; age 46.3 ± 0.5 years) were grouped by quartile of urine specific gravity (U(SG), 2007–2008 cohort) or urine osmolality (U(Osm), 2009–2010 cohort) as measures of hydration. Metabolic dysfunction was assessed by glycemic and insulinemic endpoints and by components of the metabolic syndrome. Multivariate-adjusted linear and logistic regression models were used. RESULTS: Increasing quartiles of U(SG) but not U(Osm) was associated with higher fasting plasma glucose (FPG), glycated hemoglobin (all P < 0.01), HOMA-IR and elevated insulin (all P < 0.05). Compared with the lowest quartile, those with the highest U(SG) but not U(Osm) had greater risk of metabolic syndrome (Q4 vs. Q1, OR (99% CI): 1.6 (1.0, 2.7), P = 0.01) and diabetes (Q4 vs. Q1, OR: 1.8 (1.0, 3.4), P < 0.05). Additionally, those with U(SG) > 1.013 or U(Osm) > 500 mOsm/kg, common cut-off values for optimal hydration based on retrospective analyses of existing data, had less favorable metabolic markers. In a subset of participants free from diabetes mellitus, impaired kidney function, hypertension and diuretic medication, U(SG) remained positively associated with FPG (P < 0.01) and elevated FPG (P < 0.05). CONCLUSION: These analyses provide population-based evidence that U(SG) as a proxy for hydration is associated with glucose homeostasis in NHANES 2007–2008. The same association was not significant when U(Osm) was used as a proxy for hydration in the 2009–2010 wave. CLINICAL TRIAL REGISTRY: Not applicable, as this was a reanalysis of existing NHANES data. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00394-021-02575-3.