Belgian primary school children's hydration status at school and its personal determinants.

Purpose: Dehydration has been related to several health aspects, and children are especially vulnerable. Since children spend a large time at school, we aim to examine children's hydration status at school-start and its change during the school-day by objective measures. To identify subpopulations at risk, determinants of hydration were tested.
Methods: In 371 Belgian 7-13-year-old children, hydration was measured by (1) urinary osmolality at school-start and by a pooled school-day sample; (2) body water% by impedance; (3) parental reported beverage consumption; (4) urination frequency. Linear regression analyses were used to test putative predictors of hydration status: age, sex, parental education, region (Dutch-speaking versus French-speaking part of Belgium), diet quality and adiposity.
Results: A mean osmolality of 888 mosmol/kg was found in the school-start sample and 767 mosmol/kg in the school-day sample. This resulted in, respectively, 76 and 54 % of the children being dehydrated (>800 mosmol/kg). In 45 % of the children, the hydration level decreased over the school-day. Also the body water% as derived from bio-impedance (57 % ±4), the reported average daily beverage intake (911 ml) and the lower urination frequency during weekdays versus weekend days confirmed the low hydration status in our school population. Boys, Walloon children and those with higher adiposity were at increased risk of low hydration level. Diet quality was not the predictor of hydration status.
Conclusions: Hydration status at school appeared problematic in this population. This emphasizes the need for more resources and attention by school management and governmental organizations. Herein, especially Walloon schools and boys should be reached.