xxxvi. PRC for melatonin12 July 2007 at 18:36 | Posted in Circadian rhythm | Leave a comment
Tags: Melatonin, Phase response curve
Finally! I found a picture of the Phase-Response Curve for Melatonin in humans in a presentation from ten years ago. (If you click the link and find Figure 8, you’ll also see the corresponding curves for lizards and rats.) The peak is maximum 7 hours before bedtime. Taking a melatonin pill 5-6 hours before bedtime should advance one’s circadian rhythms by upwards of an hour.
Above, I’ve added the melatonin PRC (green) to the old illustration of the light PRC (purple). Clearly, light has the greater effect. However, the effects have been shown to be additive.
Now, for some reason I’ve not seen explained, one is to ignore the rising portion of the curves. So while it looks as though the period between 4 hours and 2 hours before wake-up would give a phase advance, that is not true.