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

(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.

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.

(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.

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).

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