Association Between Increased Dietary Sodium Intake and Higher Water Intake from Fluid and Food in Children

Background and Objectives: Maintaining an appropriate hydration status is crucial for promoting health. Children, who are in the process of growth and development, are at a higher risk of insufficient water intake and dehydration. This study aimed to compare water intake among children with different levels of dietary sodium intake, and explore the relationship between hydration status, and dietary sodium intake and water intake. Methods: In this cross-sectional survey, 155 students in grades 4-6 from a primary school in Binyang County, Nanning, Guangxi, were recruited. Water intake from fluid was assessed using a validated 7-Day 24 h Fluid Intake Survey Questionnaire (days 1-7). Food intake was recorded and weighed using the duplicate diet method on days 5, 6, and 7. The water content in food was determined using the direct drying method, and dietary sodium intake was measured using inductively coupled plasma-optical emission spectrometry (ICP-OES). Urine osmolality was measured at two time points (morning and before afternoon classes) on days 5, 6, and 7 to assess hydration status. Results: A total of 155 participants (87 boys and 68 girls) completed the study, with a completion rate of 100%. The average dietary sodium intake, total water intake (TWI), water intake from fluid, and water intake from food were 1647 mg, 2039 mL, 956 mL, and 1175 mL, respectively. Among the participants, 19.4% exceeded the recommended sodium intake (2000 mg/day), 41.9% did not meet the adequate daily water intake from fluid, and 63.2% did not meet the adequate daily total water intake. When participants were divided into quartiles based on dietary sodium intake, significant differences were observed in water intake from fluid (p = 0.031) and food (p < 0.001). The water intake from fluid among participants in the HS1 (982 mL) and HS2 groups (997 mL) was higher than that among participants in LS2 (759 mL). Water intake from food increased progressively with increasing sodium intake (851 mL, 1075 mL, 1224 mL, and 1550 mL). Urine osmolality was associated with meeting the daily adequate water intake from fluid (p = 0.006), but not with exceeding the sodium intake standard (p = 0.787). There was no interaction between meeting the daily adequate water intake from fluid and exceeding the sodium intake standard (p = 0.413). Conclusions: Insufficient water intake was common among children. Children with a higher dietary sodium intake had a higher water intake from fluid and food. Urine osmolality was closely related to daily water intake from fluid, but not to sodium intake.