Figure 1.

Overall hourly mean values of casual urinary variables (urine specimens, N=13 277); Na/K ratios were highest from midnight to early morning, lower from mid-morning to mid-afternoon and higher toward evening, and statistical significance was observed between time zones (overnight, daytime, and evening) in overall participants (P<0.001) (a). Na and K concentrations were lowest from midnight to early morning, and higher from mid-morning to late evening (b, c). Urine volume was highest in the early morning and remained constant thereafter (d). Na excretion was highest in the early morning (around the time of first void after arising), and remained constant thereafter (e). K excretion increased between late morning and late afternoon, and decreased between late evening and before dawn (f). Bars indicate the 95% confidence interval of the mean.