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Melatonin-Suppression Action Spectrum and Human Health

by David M. Keith

Since the last century, information has been developed about the role of retinal ganglion cells in the control of the hormone melatonin.

Recent research has shown that:
- some retinal ganglion cells (RGCs) are non-visual photoreceptors
- the photopigment found in RGCs has been dubbed "melanopsin", and is recognized as different from any other photopigments
- radiant energy onto the retina can suppress the normal production of the neurochemical melatonin
- melatonin is the neurochemical that provides the primary control of the diurnal (day/night) cycle for most animals including humans
- the action spectrum for suppression of melatonin peaks around 464 nm, corresponding to sky blue
- disruption of the day/night cycle corresponds to increased risks for some health conditions including mood and sleep disorders, obesity, diabetes and some forms of cancer
- the presence of melatonin in the blood - as an "anti-oxidant" - reduces the start and growth of some forms of cancer
- disruption of the circadian cycle may be caused by light levels that are significantly lower than the currently-acknowledged threshold(s) for acute suppression of melatonin

A great deal of further information about these issues is available:
- one limited bibliography, compiled by D. Keith, about these issues is available here.
- an extensive, annotated bibliography, compiled by R. Wagner, is available here.
- an excellent summary of the science as of 2007 by JP Hanifin and GC Brainard is "Photoreception for circadian, neuroendocrine, and neurobehavioral regulation", J Physiol Anthropol. 2007 Mar;26(2):87-94..

The following diagram shows the action spectrum for suppression of melatonin (as developed by J. Hollan) as the blue line on the left side, along with the conventional photopic (white and gray) and scotopic (black) sensitivity functions.


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