High Sensitivity of Human Melatonin, Alertness, Thermoregulation, and Heart Rate to Short Wavelength Light

Abstract

Light can elicit acute physiological and alerting responses in humans, the magnitude of which depends on the timing, intensity, and duration of light exposure. Here, we report that the alerting response of light as well as its effects on thermoregulation and heart rate are also wavelength dependent. Exposure to 2 h of monochromatic light at 460 nm in the late evening induced a significantly greater melatonin suppression than occurred with 550-nm monochromatic light, concomitant with a significantly greater alerting response and increased core body temperature and heart rate ( approximately 2.8 x 10(13) photons/cm(2)/sec for each light treatment). Light diminished the distal-proximal skin temperature gradient, a measure of the degree of vasoconstriction, independent of wavelength. Nonclassical ocular photoreceptors with peak sensitivity around 460 nm have been found to regulate circadian rhythm function as measured by melatonin suppression and phase shifting. Our findings-that the sensitivity of the human alerting response to light and its thermoregulatory sequelae are blue-shifted relative to the three-cone visual photopic system-indicate an additional role for these novel photoreceptors in modifying human alertness, thermophysiology, and heart rate.

What Keeps Us Awake?—the Role of Clocks and Hourglasses, Light, and Melatonin

“…In fact, a change in the timing of the external LD cycle leads to a shift in endogenous phase of circadian rhythms (Brainard et al, 1997). Besides these long-term effects on circadian phase, many acute effects of light have been consistently shown for a wide range of physiological processes, such as hormonal secretion, heart rate, sleep propensity, alertness, body temperature, pupillary constriction, and gene expression (Aalto and Hilakivi, 1986;Badia et al, 1991;Berson, 2003;Cajochen et al, 1992Cajochen et al, , 1996Cajochen et al, , 2005Cajochen et al, , 2006Lavoie et al, 2003;Muñoz et al, 2005). Both long-term and acute effects of light are usually referred to as non visual (or non-image forming, NIF) effects, since they drift apart from the classical involvement of rod and cone photopigments in the visual responses to light.…”

Artificial light-at-night – a novel lifestyle risk factor for metabolic disorder and cancer morbidity

“…ALAN, as the most prominent circadian disruptor, vigorously ceases pineal MLT synthesis and secretion and consequently disrupts circadian rhythms [31,41]. The melanopsin-containing ipRGCs, which regulate the pineal MLT synthesis via the SCN, are extremely sensitive to short wavelength light exposure even at low irradiance [42] and for a short period [43] as they can suppress the synthesis of the pineal hormone MLT. The spectral sensitivity of MLT synthesis suppression demonstrates wavelength-dependent sensitivity with robust effects in response to short wavelength (450-500 nm) exposure [44,45].…”

La lumière comme stimulant de l’activité cognitive cérébrale

“…Nos résultats pointent vers un élargissement graduel de l'impact de la lumière avec sa durée et son intensité, qui se traduit progressivement par un effet comportemental. En accord avec ces propositions, d'autres études utilisant uniquement des variables comportementales ou électroencéphalographiques (EEG) ont rapporté un impact significatif au bout de 30 min d'illumination avec des lumières bleues, ou enrichies en bleu, de longueur d'onde et d'intensité comparables à celles que nous avons employées [15,16,21,22]. La durée, l'intensité et la longueur d'onde ne sont cependant pas les seuls aspects à prendre en considé-ration lors de l'administration d'une exposition lumineuse.…”

“…Tout comme d'autres travaux utilisant des lumières de différentes longueurs d'onde et de différentes intensités avec d'autres protocoles [15,16,21,22], elles mettent en avant l'impact non visuel de la lumière. Elles renforcent l'idée selon laquelle il est important de considérer la lumière et ses fonctions non visuelles lorsqu'on s'expose à la lumière.…”