Circadian rhythm in serum iron levels.

This study was aimed at assessing the circadian rhythm of serum iron levels in Chinese healthy subjects. The project was conducted in 19 healthy, Chinese male subjects following a 4-day diet equilibration. Blood samples were collected on day 5 at 0800, 1000, 1200, 1400, 1600, 1800, 2000, and 2400 hours to determine endogenous serum iron concentrations. Iron concentrations were determined using an inductively coupled plasma mass spectrometry. Iron concentration was decreased from morning to afternoon. The minimum value of iron level was 1,987 μg/L at 2000 hours while the maximum was 2,229 μg/L at 1000 hours, and 2,278 μg/L at 1400 hours, respectively, the amplitude was 291 μg/L. This study indicates that when assessing the bioequivalence of iron formulations, baseline levels of iron (obtained before dosing) should not be subtracted simply from the amount obtained on the drug dosing day to yield the net effect of iron formulation administration. More valid methods to optimize the design of such bioequivalence studies should be taken into consideration.