High Sensitivity of the Human Circadian Melatonin Rhythm to Resetting by Short Wavelength Light

Abstract

The endogenous circadian oscillator in mammals, situated in the suprachiasmatic nuclei, receives environmental photic input from specialized subsets of photoreceptive retinal ganglion cells. The human circadian pacemaker is exquisitely sensitive to ocular light exposure, even in some people who are otherwise totally blind. The magnitude of the resetting response to white light depends on the timing, intensity, duration, number and pattern of exposures. We report here that the circadian resetting response in humans, as measured by the pineal melatonin rhythm, is also wavelength dependent. Exposure to 6.5 h of monochromatic light at 460 nm induces a two-fold greater circadian phase delay than 6.5 h of 555 nm monochromatic light of equal photon density. Similarly, 460 nm monochromatic light causes twice the amount of melatonin suppression compared to 555 nm monochromatic light, and is dependent on the duration of exposure in addition to wavelength. These studies demonstrate that the peak of sensitivity of the human circadian pacemaker to light is blue-shifted relative to the three-cone visual photopic system, the sensitivity of which peaks at approximately 555 nm. Thus photopic lux, the standard unit of illuminance, is inappropriate when quantifying the photic drive required to reset the human circadian pacemaker.

Light-induced melatonin suppression: age-related reduction in response to short wavelength light

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Circadian genes, rhythms and the biology of mood disorders

“…This could be due to the ability of certain wavelengths of light to more effectively control circadian rhythms (Foster and Helfrich-Forster, 2001). Recent studies have found that light in the blue spectrum (446-477) outperforms other wavelengths in melatonin suppression, circadian phase shifting, and antidepressant effects (Brainard et al, 2001;Thapan et al, 2001;Lockley et al, 2003;Glickman et al, 2006). While there have been several studies that have investigated the mechanism by which light shifts the circadian clock and the specific photoreceptors involved in this effect (Foster and Helfrich-Forster, 2001;Foster et al, 2003), few studies have examined the effects of light-induced circadian phase shifting as an antidepressant in animal models.…”

Effects of Artificial Dawn on Subjective Ratings of Sleep Inertia and Dim Light Melatonin Onset

“…In our study, light was not only in the low range of intensities (Zeitzer et al, 2005), but it was also shifted to the long wavelength range of the visible spectrum. It has been extensively shown that the circadian system is more sensitive to short wavelengths (Brainard et al, 2001;Cajochen et al, 2005;Lockley et al, 2003;Revell et al, 2005Revell et al, , 2006Thapan et al, 2001). Higher intensities of long wavelengths of light could have shifted the DLMO (Hanifin et al 2006;Zeitzer et al 1997), but they may also lead to undesired earlier wakefulness.…”