Effect of the menstrual cycle stage on the melatonin suppression by dim white light.

Patients with bipolar disorder have been shown to have a supersensitive melatonin suppression to dim white light (200 and 500 lux) compared to normal healthy subjects. Previous studies suggest menstrual cycle dependent changes in the melatonin rhythm, but it is not known if the melatonin sensitivity to light changes during the menstrual cycle. The present study investigated the melatonin suppression to dim white light (200 lux) in different stages of the menstrual cycle. No significant differences in the percent suppression of melatonin were found across the stages of the menstrual cycle (p = .97). Our findings suggest that the menstrual cycle hormonal changes do not affect the melatonin sensitivity to dim light in healthy controls.