"On a daily basis, millions of people choose to keep the lights on prior to bedtime and during the usual hours of sleep," said Joshua Gooley, PhD, of Brigham and Women's Hospital and Harvard Medical School in Boston, Mass. and lead author of the study. "Our study shows that this exposure to indoor light has a strong suppressive effect on the hormone melatonin. This could, in turn, have effects on sleep quality and the body's ability to regulate body temperature, blood pressure and glucose levels."
The study is reported here and the abstract is below. It gets a bit scary:
"Given that chronic light suppression of melatonin has been hypothesized to increase relative risk for some types of cancer and that melatonin receptor genes have been linked to type 2 diabetes, our findings could have important health implications for shift workers who are exposed to indoor light at night over the course of many years," said Gooley. "Further research is still needed to both substantiate melatonin suppression as a significant risk factor for breast cancer and determine the mechanisms by which melatonin regulates glucose metabolism."But this is all standard Robb Wolf / Lights Out stuff.
Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans.
Context: Millions of individuals habitually expose themselves to room light in the hours before bedtime, yet the effects of this behavior on melatonin signaling are not well recognized. Objective: We tested the hypothesis that exposure to room light in the late evening suppresses the onset of melatonin synthesis and shortens the duration of melatonin production. Design: In a retrospective analysis, we compared daily melatonin profiles in individuals living in room light (<200 lux) vs. dim light (<3 lux). Patients: Healthy volunteers (n = 116, 18-30 yr) were recruited from the general population to participate in one of two studies. Setting: Participants lived in a General Clinical Research Center for at least five consecutive days. Intervention: Individuals were exposed to room light or dim light in the 8 h preceding bedtime. Outcome Measures: Melatonin duration, onset and offset, suppression, and phase angle of entrainment were determined. Results: Compared with dim light, exposure to room light before bedtime suppressed melatonin, resulting in a later melatonin onset in 99.0% of individuals and shortening melatonin duration by about 90 min. Also, exposure to room light during the usual hours of sleep suppressed melatonin by greater than 50% in most (85%) trials. Conclusions: These findings indicate that room light exerts a profound suppressive effect on melatonin levels and shortens the body's internal representation of night duration. Hence, chronically exposing oneself to electrical lighting in the late evening disrupts melatonin signaling and could therefore potentially impact sleep, thermoregulation, blood pressure, and glucose homeostasis.