Transcranial bright light exposure via ear canals does not suppress nocturnal melatonin in healthy adults – A single-blind, sham-controlled, crossover trial

Abstract

We investigated whether transcranial bright light (TBL) affects nocturnal melatonin and cortisol secretion in sham-controlled crossover trial. Young healthy adults were exposed in random order to 24 minutes of TBL or sham exposure via ear canals at 01:10 h. Saliva and urine samples were collected hourly between 21 h–03 h and 06 h–09 h. There were no significant differences in melatonin or cortisol concentrations between TBL and sham exposures at any sampling point indicating that TBL via ear canals does not suppress nocturnal melatonin secretion. Thus, non-visual effects of TBL are mediated via a pathway not involving melatonin suppression.

• Circadian rhythm
• cortisol
• ear light
• melatonin
• opsins
• saliva

Acknowledgments

The authors thank laboratory technicians Ms. Helka Koisti and Ms. Marja-Liisa Martimo-Halmetoja for their contribution with the laboratory analyses.