Inadequate Hydration, BMI, and Obesity Among US Adults: NHANES 2009–2012

PURPOSE Improving hydration is a strategy commonly used by clinicians to prevent overeating with the goal of promoting a healthy weight among patients. The relationship between weight status and hydration, however, is unclear. Our objective was to assess the relationship between inadequate hydration and BMI and inadequate hydration and obesity among adults in the United States.

METHODS Our study used a nationally representative sample from the National Health and Nutrition Examination Survey (NHANES) 2009 to 2012, and included adults aged 18 to 64 years. The primary outcome of interest was body mass index (BMI), measured in continuous values and also categorized as obese (BMI ≥30) or not (BMI <30). Individuals with urine osmolality values of 800 mOsm/kg or greater were considered to be inadequately hydrated. Linear and logistic regressions were performed with continuous BMI and obesity status as the outcomes, respectively. Models were adjusted for known confounders including age, race/ethnicity, sex, and income-to-poverty ratio.

RESULTS In this nationally representative sample (n = 9,528; weighted n = 193.7 million), 50.8% were women, 64.5% were non-Hispanic white, and the mean age was 41 years. Mean urine osmolality was 631.4 mOsm/kg (SD = 236.2 mOsm/kg); 32.6% of the sample was inadequately hydrated. In adjusted models, adults who were inadequately hydrated had higher BMIs (1.32 kg/m²; 95% CI, 0.85–1.79; P <.001) and higher odds of being obese (OR = 1.59; 95% CI, 1.35–1.88; P <.001) compared with hydrated adults.

CONCLUSION We found a significant association between inadequate hydration and elevated BMI and inadequate hydration and obesity, even after controlling for confounders. This relationship has not previously been shown on a population level and suggests that water, an essential nutrient, may deserve greater focus in weight management research and clinical strategies.