Underhydration Is Associated with Obesity, Chronic Diseases, and Death Within 3 to 6 Years in the U.S. Population Aged 51-70 Years

Abstract

Nationally representative data from the National Health and Nutrition Examination Survey (NHANES) indicate that over 65% of adults aged 51-70 years in the U.S. do not meet hydration criteria. They have hyponatremia (serum sodium < 135 mmol/L) and/or underhydration (serum sodium >145 mmol/L, spot urine volume <50 mL, and/or spot urine osmolality ≥500 mmol/kg). To explore potential public health implications of not meeting hydration criteria, data from the NHANES 2009-2012 and National Center for Health Statistics Linked Mortality Files for fasting adults aged 51-70 years (sample n = 1200) were used to determine if hyponatremia and/or underhydration were cross-sectionally associated with chronic health conditions and/or longitudinally associated with chronic disease mortality. Underhydration accounted for 97% of the population group not meeting hydration criteria. In weighted multivariable adjusted Poisson models, underhydration was significantly associated with increased prevalence of obesity, high waist circumference, insulin resistance, diabetes, low HDL, hypertension, and metabolic syndrome. Over 3-6 years of follow-up, 33 chronic disease deaths occurred in the sample, representing an estimated 1,084,144 deaths in the U.S. Alongside chronic health conditions, underhydration was a risk factor for an estimated 863,305 deaths. Independent of the chronic health conditions evaluated, underhydration was a risk factor for 128,107 deaths. In weighted multivariable Cox models, underhydration was associated with 4.21 times greater chronic disease mortality (95% CI: 1.29-13.78, p = 0.019). Zero chronic disease deaths were observed for people who met the hydration criteria and did not already have a chronic condition in 2009-2012. Further work should consider effects of underhydration on population health.

Keywords: chronic disease; hydration; mortality.

Figure 1

Directed acylic graph (DAG) representing the hypothesized joint effect of hydration classification and chronic health condition on death. The yellow circle highlights the joint exposure. The blue circles represent the outcome. The pink and grey circles represent covariates that were observed and unobserved by National Health and Nutrition Examination Survey (NHANES), respectively. The DAG assumes that the hydration classification is a function of water intake requirements, water intake, and health condition. Many unobserved covariates and interrelationships between covariates are not shown. Figure 1 was generated using DAGgity.net v2.3.

Figure 2

Distribution of serum sodium and urine osmolality in the study sample.

Figure 3

Kaplan–Meier curves for (a) all-cause and (b) chronic disease-associated mortality associated with hyponatremia, euhydration, or underhydration in 2009–2012 for U.S. adults aged 51–70 years. Hyponatremia: serum sodium below 135 mmol/L; euhydration: serum sodium 135–144 mmol/L, urine volume 50 mL or higher, and urine osmolality below 500 mmol/kg; underhydration: serum sodium 145 mmol/L or higher, urine volume below 50 mL, or urine osmolality 500 mmol/kg or higher.

Figure 4

Kaplan–Meier curves for (a) all cause and (b) chronic disease-associated mortality by chronic health condition and hydration classification in 2009–2012 for U.S. adults aged 51–70 years. Hyponatremia: serum sodium below 135 mmol/L; euhydration: serum sodium 135–144 mmol/L, urine volume 50 mL or greater, and urine osmolality below 500 mmol/kg; underhydration: serum sodium 145 mmol/L or higher, urine volume below 50 mL, or urine osmolality 500 mmol/kg or higher. Chronic health conditions: obesity, high waist circumference, insulin resistance, diabetes, elevated glucose, elevated HgA1c, elevated triglycerides, low HDL, hypertension, and metabolic syndrome in 2009–2012.