11, 12, 13, 14 However, it is not known whether these estimation methods are applicable to adolescents whose body size varies depending on their developmental stage. Because a 24-h mineral and creatinine excretion is associated with adult height, weight and age, these have been used to estimate daily sodium and potassium excretion. One downfall of the 24-h urine collection is the inconvenience it poses for study participants. 9, 10 Thirty years ago, Moriyama and Saito 9 studied 24-h sodium and potassium excretion in children aged 1–18 years, but the age range was wide, and the variance in excretion increased as the age increased. However, among Japanese children and adolescents, correct measurements of dietary salt intake using 24-h urinary excretion are scarce. 4 Considering the maintenance of similar dietary habits from childhood into adulthood, 8 it is important to have an adequate understanding of salt intake and to control dietary salt intake from a very young age. In children, dietary salt intake is also related to blood pressure, 7 and the WHO strongly recommends a low salt intake, as well as a high, energy-based potassium intake to prevent adult hypertension. 4 In Japan, although dietary salt intake has decreased over the past several decades, it exceeds the Japanese recommendations of <8.0 g for men and <7.0 g for women, which are higher than the WHO recommendations. 3 The World Health Organization (WHO) recommends a salt intake <5 g per day to decrease blood pressure and reduce the risk of cardiovascular diseases. High salt intake is a possible cause of adult hypertension, 1 cardiovascular diseases 2 and gastric cancer. Therefore, the estimation methods used in adults are not applicable for use in adolescents. Excretion was associated more with physical activity than with bodyweight. We described daily sodium and potassium excretion in Japanese secondary schoolchildren.
Potassium excretion was associated with height and physical activity. Sodium excretion was associated with sodium and potassium concentrations in overnight urine samples and physical activity. Estimated usual potassium intake was 2195±4☖30 mg per day for the boys and girls, respectively. The 24-h potassium excretion was 43.4☑0.8 and 45.8☑4.4 mmol per 24 h for the boys and girls, respectively.
Considering daily habits and loss from sweat, intake was assumed to be 10.6☑.2 and 10.0☒.4 g per day for the boys and girls, respectively. The 24-h sodium excretion was 163.2☓6.8 and 149.8±45.1 mmol per 24 h for the boys and girls, respectively. We analyzed the 24-h samples with a >20-h collecting period and no missed voiding. Body height and weight were measured, and menstruation and physical activity were assessed via questionnaires. Sodium, potassium and creatinine concentrations were analyzed. The 24-h urine samples and first morning voiding (overnight) samples were collected twice from 68 secondary schoolchildren in Suo-Oshima Town, Japan. Some evidence indicates that sodium and potassium intake has been correctly measured, but information concerning these associated factors is scarce.
Data on the sodium and potassium intake using dietary records among schoolchildren are sorely lacking in the Japanese literature.
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