An exploratory study of the relationship between the midday-midnight law and electrical conduction properties of corresponding acupuncture points.

The midday-midnight law is a well-known empirical law in Oriental medicine stating that the circadian rhythm of internal organs influences their paired organs according to the time of day. However, there has been little research to test the purported relationship between the time of day and organ function. The purpose of this preliminary study was to investigate whether the midday-midnight law applies to the meridian activity and the electrical conduction properties of the acupuncture points. We used the digital readout instrument (MERIDIAN) to measure electrical conduction properties at 12 acupuncture points corresponding to the 12 meridians at four times: 12:00, 14:00, 22:00, and 24:00 hours. There were no significant differences in the electrical current values measured at the four times in any meridian. However, the mean current values of 12 acupuncture points changed significantly over time (P < 0.0001). The mean current values were significantly higher at 14:00 (P < 0.001), 22:00, and 24:00 hours (P < 0.001) than at 12:00 hours. The highest current value occurred at 22:00 hours and was significantly higher than 24:00 hours (P < 0.05). Although these do not conclusively support the traditional midday-midnight theory, our data suggest the existence of some type of daily variability in electrical current.