The effect of voluntary dehydration on cognitive functions of elementary school children

Acta Paediatr. 2005 Nov;94(11):1667-73. doi: 10.1080/08035250500254670.


Aims: (1) To describe the occurrence of voluntary dehydration in two classes of elementary school students as expressed by their morning and noon-time urine osmolality; and (2) to determine the relationship between the children's scores on cognitive tests and their state of hydration.

Methods: Group comparison among fifty-eight sixth-grade students (age range 10.1-12.4 y old) during mid-June at two schools in a desert town. Morning and noon-time urine samples were collected in school, and five cognitive tests were scored in the morning and at noon-time.

Main outcome measures: (1) morning and noon-time urine osmolality; (2) scores of five cognitive tests (hidden figures, auditory number span, making groups, verbal analogies, and number addition) that were applied in the morning and at noon-time.

Results: Thirty-two students were dehydrated (urine osmolality above 800 mosm/kg H(2)O) in the morning. An individual's noon-time urine osmolality was highly related to morning osmolality (r=0.67, p=0.000). The morning cognitive scores were similar in the hydrated and dehydrated students (p=0.443). The adjusted mean scores of the noon-time tests, with the morning test scores as covariates, demonstrated an overall positive trend in four of the five tests in favor of the hydrated group (p=0.025). The effect was mainly due to the auditory number span test (p=0.024).

Conclusion: Voluntary dehydration is a common phenomenon in school-aged children that adversely affects cognitive functions.

Publication types

  • Multicenter Study

MeSH terms

  • Child
  • Cognition*
  • Dehydration / epidemiology
  • Dehydration / psychology*
  • Drinking Behavior*
  • Female
  • Humans
  • Israel / epidemiology
  • Male
  • Multivariate Analysis
  • Osmolar Concentration
  • Prevalence
  • Students / psychology*
  • Urine / chemistry