Inhibition of melatonin secretion onset by low levels of illumination

Abstract

Melatonin is a hormone released during darkness under the control of the hypothalamic circadian pacemaker. It has been shown that melatonin is suppressed by light as a function of intensity, with low levels of illumination producing small effects and more intense light greater, but not complete inhibition. The studies which lead to these conclusions administered light subsequent to the secretion pattern being well established. Light as low as 250 lux administered during the normal onset of secretion can reduce melatonin to below detectable levels. The onset of melatonin secretion was delayed for at least an hour during 250 lux exposure and did not rise until termination of light exposure (two hours after control melatonin onset) with higher illumination (500, 1000 and 2500 lux). This tentatively indicates that duration of the inhibition is intensity dependent. It is suggested that the experimental paradigm used in the present study may be a more realistic representation of the effect of normal light exposure (both natural and artificial) on the circadian system, and that findings may be pertinent to the aetiology of certain sleep onset insomnias, which would include delayed sleep phase syndrome (DSPS) and adaptation to shift work.

The Influence of Light at Night Exposure on Melatonin Levels among Canadian Rotating Shift Nurses

“…Experimental studies have shown a dose-response relationship between light exposure and melatonin levels, in which increased light is associated with decreased melatonin production (31)(32)(33)(34)(35). Epidemiologic studies, primarily among shift workers, have used multiple methods to assess exposure (36)(37)(38)(39)(40)(41) and results generally show an inverse relationship between light and melatonin (36)(37)(38)(39)(40)(41).…”

“…Therefore, observational studies with comparisons of chronologic time points between shift groups are needed to determine whether the relationship between light and melatonin in experimental work (31)(32)(33)(34)(35) is also seen in the context of an observational study. Recent work also indicates a need to incorporate other factors related to melatonin production, such as chronotype, when investigating these relationships (42).…”

Western lifestyle and immunopathology of multiple sclerosis

“…Interestingly, in a mouse model of MS, sleep fragmentation before and after EAE induction led to a worse disease outcome by promoting leukocyte infiltration across the BBB and impairing immune regulation, but termination of sleep fragmentation improved EAE scores in these mice compared with mice that had normal sleep pattern 178. Light exposure at night and sleep deprivation suppress circulating levels of melatonin,179, 180 a hormone released by the pineal gland during the dark phase that plays a critical role in the regulation of circadian and seasonal rhythms 181. A role for melatonin in MS has been suggested by several clinical observations.…”

Effects of Electromagnetic Radiation (Bright Light, Extremely Low-Frequency Magnetic Fields, Infrared Radiation) on the Circadian Rhythm of Melatonin Synthesis, Rectal Temperature, and Heart Rate.

“…This rather low illumination suppressed melatonin synthesis nevertheless completely in any of the 7 subjects. This is explained by the fact that the period between the onset and the acrophase of melatonin synthesis is particularly sensitive against melatonin suppressive stress 3,4) . Exposure in the present study was terminated well before the (usual) offset of melatonin synthesis, thus allowing rebound effects, which are differently understood in the literature.…”

“…The period of the usual onset and rise of nocturnally elevated melatonin synthesis seems to be particularly sensitive not only to light but also to the impact of magnetic fields 3,4) . Similar, but far smaller effects were evoked in animal experiments by other parts of the electromagnetic spectrum 5) , namely by UV-A radiation 6) and extremely low-frequency magnetic fields 7) .…”