Removing masking factors from urinary rhythm data in humans.

We have previously developed simple models that enable the exogenous and endogenous components of the circadian rhythm of body temperature to be separated. The present paper extends the method to urinary data. First, we have shown that the basic superiority of the two-component model over the one-component model persists when temperature data are converted into a format that is appropriate for urine sampling (that is, a single overnight sample and two-hourly samples during waking). Second, we provide normative endogenous data for urinary sodium, potassium and urate, data obtained from about 80 constant routines. These data are required for the two-component model. Third, we have compared the rate of adjustment to a simulated eastward time-zone transition of 8 hr in 8 subjects. This showed that the rate of adjustment assessed by the two-component model was significantly less than that assessed by the one-component model and much closer to that assessed in separate experiments (n = 15 subjects) using constant routines. We conclude that the two-component model can be used upon urinary data to give a closer approximation to the shift of the endogenous component, as assessed by constant routines, than can estimates that do not take into account the problem of masking caused by exogenous factors.