The Severity of Obesity Promotes Greater Dehydration in Children: Preliminary Results

The state of hydration of the body depends on the balance between the amount of water and salt consumed and excreted (the urinary extraction of excess sodium requires water). Inappropriate nutrition, particularly consuming too much processed food, causes obesity in children and additionally causes excessive sodium consumption, thus increasing the risk of excessive water loss. The aim of this study was to assess the hydration status of children with obesity and the relation between hydration, body composition, urinary sodium extraction, and nutrient intake. The study group consisted of 27 patients with obesity, with a mean age of 12.89 ± SD 2.79. Each patient's height, weight, body composition (electrical bioimpedance (BIA)), diet (7-day record), and biochemical tests were assessed. The hydration status was assessed using 24-hour urine collection, 24-hour urine osmolality, and an ultrasound of the vena cava (IVC/Ao index). Overall, 55% of children (n = 15) had urine osmolality values above 800 mOsm/kgH₂O, which indicates significant dehydration, and 53% (n = 14) were dehydrated, based on the IVC/Ao index. Children with obesity and dehydration had a significantly higher BMI (31.79 vs. 27.32; p = 0.0228), fat mass percentage (37.23% vs. 30.07% p = 0.0051), and fat mass in kg (30.89 vs. 20.55; p = 0.0158), and significantly higher sodium intake from their diet (3390.0 mg vs. 2921.0 mg; p = 0.0230), as well as their sodium/potassium ratio (2.4 vs. 2.0; p = 0.0043). The 24-hour urinary sodium excretion and osmolality values were directly related to fat-mass percentage and fat-mass (in kg) in a simple linear correlation analysis. Our preliminary results confirm that obesity is related to dehydration. The overall high sodium excretion in children with obesity indicates an excessive salt intake along with low potassium intake, which is a significant predictor of dehydration, regardless of the total water intake (TWI).