Background: The purpose of this study was to investigate the relationship between salt intake and urinary salt excretion and to examine the validity of a self-monitoring device for estimating 24-h urinary salt excretion from overnight urine samples. Methods: Twelve young, healthy female volunteers consumed test meals from days 1 to 14 and estimated urinary salt excretion on days 2-15 by using a self-monitoring device. The salt content of the test meals was as follows: 10 g (days 1-5), 6 g (days 6-8), 13 g (days 9-11), 6 g (day 12), 13 g (day 13), and 6 g (day 14). Results: The average 24-h urinary salt excretion (the ratio of urinary salt excretion to salt intake of the previous day) estimated from the overnight urine samples was as follows: 8.01±1.15 g (0.73±0.11) on days 2-6, 5.86±0.85 g (1.01±0.15) on days 7-9, 9.69±1.64 g (0.74±0.13) on days 10-12, 6.51±1.56 g (1.03±0.25) on day 13, 8.60±3.25 g (0.71±0.14) on day 14, and 6.28±1.31 (1.05±0.22) on day 15. Thus, the salt excretion/salt intake ratio was approximately 0.8 during the high-salt phase and 1.0 during the low-salt phase. Conclusion: The estimation of 24-h urinary salt excretion from overnight urine samples by using a self-monitoring device is a reasonably valid method in this young and healthy female population for detecting daily changes in salt intake.
