Abstract
Food habits during infancy may affect salt intake in adulthood. Therefore it is important to determine dietary salt intake in normal infants, for which estimation based on urinary sodium excretion can be regarded as the gold standard. Accurate estimation of 24-hour urine volume is a prerequisite of this method. Therefore, we used this method to collect 24-hour urine and estimated the 24-hour urine volume in healthy infants. We collected overnight urine and 24-hour urine from healthy infants aged 3 to 5 years in Miyagi prefecture, Japan, three times from February to December, 2003, and once in 2005. In the latter examination, we modified the method so as to encourage infants to cooperate. Means were compared by analysis of variance and multiple. Differences between means were considered significant at p<0.05. We used data from 237 infants. Volumes of overnight urine and 24-hour urine were higher in measurements conducted in 2005 than in 2003, although there was no difference between the sexes. The difference in 24-hour urine volume between 2003 and 2005 was likely due to the loss of urine in 2003, which was overcome by the methodological improvement in 2005. The correlation coefficient between overnight urine volume and 24-hour urine volume was not very high (r<0.60). The correlation coefficient between 24-hour urine volume and parameters such as age, body height and body mass was significant (p<0.001) but not very high (r<0.26). The overnight urine volume, 24-hour urine volume and 24-hour urine volume per body height were estimated to be 165 mL/d, 533 mL/d and 518 mL/m/d in the present study.
