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Extraocular light exposure does not suppress plasma melatonin in humans
S W Lockley1, D J Skene, K Thapan
1School of Biological Sciences, University of Surrey, Guildford, UK.
The Journal of Clinical Endocrinology and Metabolism
|September 24, 1998
Summary
Extraocular light exposure does not suppress melatonin synthesis. This study found that light applied to the skin, not the eyes, did not affect nighttime melatonin levels in humans.
Area of Science:
- Chronobiology
- Neuroendocrinology
- Human Physiology
Background:
- Light exposure influences the circadian axis through melatonin suppression and circadian oscillator phase-shifts.
- Recent research suggests extraocular light exposure may induce circadian clock phase-shifts.
Purpose of the Study:
- To investigate if extraocular light exposure can suppress pineal melatonin synthesis.
- To determine if light applied to the skin affects melatonin levels, similar to ocular light exposure.
Main Methods:
- Study 1: Ocular exposure to white light (2250 lux, 30 min) via fiber optic cable.
- Study 2: Extraocular exposure to higher intensity light (14,000-67,500 lux, 180 min) to the popliteal region, with eyes shielded.
Main Results:
- Ocular light exposure significantly suppressed nighttime plasma melatonin levels (61 +/- 6%).
- Extraocular light exposure did not suppress plasma melatonin levels (4 +/- 7%).
Conclusions:
- Extraocular light exposure does not appear to influence the suprachiasmatic nucleus-pineal pathway for melatonin synthesis.
- Mammalian extraocular photoreception, if present, does not mediate melatonin suppression.