Prevalence of voluntary dehydration according to urine osmolarity in elementary school students in the metropolitan region of São Paulo, Brazil

OBJECTIVES: To evaluate the prevalence of voluntary dehydration based on urine osmolarity in elementary school students from two public educational institutions in the metropolitan region of São Paulo and evaluate whether there is a relationship between voluntary dehydration and nutritional status or socioeconomic status. METHODS: Analytical cross-sectional study with students from two public schools in the city of Osasco. The determination of urine osmolarity was performed using the freezing method of the Advanced® Osmometer Model 3W2. Urine osmolarity greater than 800 mOsm/kg H2O was considered voluntary dehydration. During data collection, the weights and heights of the students, environmental temperatures and air humidity levels were obtained. RESULTS: A total of 475 students aged six to 12 years were evaluated, of whom 188 were male. Voluntary dehydration occurred in 63.2% of the students and was more frequent in males than in females. The prevalence of voluntary dehydration was more frequent in males aged six to nine years than in females. However, no statistically significant difference was observed between males and females aged 10 to 12 years. No association was found between voluntary dehydration and nutritional status or socioeconomic status. CONCLUSION: The prevalence of voluntary dehydration was high in elementary school students and was more frequent in males. No association was found between voluntary dehydration and nutritional or socioeconomic status.

Relationship between Nocturnal Polyuria and Antidiuretic Hormone in Chronic Spinal Cord Injury

OBJECTIVE: To delineate the role of antidiuretic hormone (ADH) in relation to nocturnal polyuria, and to identify the factors influencing on the diurnal antidiuretic hormone level. METHOD: The ADH was measured by radioimmuoassay at daytime (2:00 PM) and at nighttime (2:00 AM) with nocturnal polyuria group (11) and without nocturnal polyuria group (8). Urine volume, serum osmolarity, urine osmolarity, and blood pressure were also measured at the same time. RESULTS: 1) The ADH at 2:00 AM did not increase in nocturnal polyuria group, although it increased in no-symptom group. 2) There was a statistically significant correlation between wheelchair ambulation time and daytime ADH level. 3) The difference of ADH level between daytime and nighttime showed decrease in orthostatic hypotension group. CONCLUSION: There was relationship between nocturnal polyuria and diurnal variation of ADH level. The ADH concentration seems to be influenced by the postural factors and sympathetic factors.