Hydration and obesity among outpatient-based population: H2Ob study.

Recent evidence suggests that obese people are hypohydrated and that water consumption may be a useful indicator for the prevention and treatment of obesity. Nevertheless, there is no agreement regarding the best hydration status indicators and there are few data about the relationship between hydration and body weight. In the present study, we aim to analyze the correlation among hydration status with obesity measured by three different methods (plasma osmolarity, urinary specific gravity (USG) and urinary osmolarity) in a hospital-based outpatient population. We have carried out a cross-sectional study to evaluate the association between obesity and hydration status in 260 patients, average 56.5±15.7 years. Hydration status was estimated by means of plasma osmolarity, urine osmolarity and USG. We did show significant trend of higher urine osmolarity (P=0.03), USG (P=0.000) and plasma osmolarity (P=0.000) with an increase of weight status categories, more accurate in the case of plasma osmolarity. In a multivariate analysis, after controlled by confounders, we found that obesity was associated with plasma osmolarity (OR 1.09; 95% CI 1.02 to 1.17, P=0.009), urine osmolarity (OR 1.00; 95% CI 1.00 to 1.01, P=0.05) and USG (OR 1.02; 95% CI 1.00 to 1.04, P=0.05). Our results have shown a more accurate relationship between plasma osmolarity with all body mass index categories. This finding may have clinical implications that must be confirmed in further studies.