In normal healthy individuals, there is a 12-hour and 24-hour circadian rhythm of serum phosphorus (serum P) with a nadir in early-mid morning, a rise to a minor peak in the afternoon (around 4:00PM), and a further rise to a major peak just after midnight. In a study of 6 healthy male patients, Portale et al found that the 12-hour component is modified by dietary P intake whereas the 24-hour rhythm in serum P is independent of the intake of phosphorus. Additionally, this trial demonstrated a large swing in amplitude between peak and nadir serum P in the normal healthy subjects (1.2 mg/dL) and also demonstrated a large difference in mean 24-hour serum P with normal vs. high dietary P intake, however no difference in fasting AM serum P results was observed. These findings may suggest the poor performance of serum P as a biomarker of intervention aimed at P load reductions via treatment options such as phosphate binders or salivary P-binder chewing gum.