Category: Studies

2011 study

Laura K. Fonken, Randy J. Nelson

Department of Neuroscience and The Institute for Behavioral Medicine Research, The Ohio State University

Technological advances, while providing many benefits, often create circumstances that differ from the conditions in which we evolved. With the wide-spread adoption of electrical lighting during the 20^thcentury, humans became exposed to bright and unnatural light at night for the first time in their evolutionary history. Electrical lighting has led to the wide-scale practice of 24-hour shift-work and has meant that what were once just “daytime” activities now run throughout the night; in many ways Western society now functions on a 24-hour schedule. Recent research suggests that this gain in freedom to function throughout the night may also come with significant repercussions. Disruption of our naturally evolved light and dark cycles can result in a wide range of physiological and behavioral changes with potentially serious medical implications. In this article we will discuss several mechanisms through which light at night may exert its effects on cancer, mood, and obesity, as well as potential ways to ameliorate the impact of light at night.

At different times during our respective childhoods, we both toured Carlsbad Caverns in New Mexico. As part of the tour, the lights in the cave were turned off. The darkness was incredible, engulfing absolutely everything. In our society, we rarely experience such profound darkness; every night, our homes, work places, and streets are brightly illuminated by the glow of electric lights. We will of course always be naturally illuminated by the stars and the moon on a clear night, but we can safely say that most of the light we experience at night is unnatural.

Humans are diurnal, that is, we evolved to be active during the day and to sleep at night. As such, we never developed the ability to see well in the dark. Over time, we have, however, developed the desire to do more and more during the time we are awake, be it night or day, and so we have created an environment that corrects for our relative night blindness. Since the advent of electrical lighting around the turn of the 20^thcentury, humans have become increasingly exposed to bright and unnatural light at night. Urban development has further exacerbated the issue, with lighting from infrastructure straying into the atmosphere nightly (Figure 1). Today, 99% of the population in the United States and Europe, and 62% of the world’s remaining population, are exposed to this “light pollution” [1]. There is no denying that the invention of electrical lighting was a boon for developing industry and technology, allowing the extension of the workday into the night and boosting economic development. However, the use of light at night continues to rapidly increase (by 6% per year) [1] without thorough (or any) consideration of its biological implications.

.

.

.

A common risk factor in many of the pathologies associated with exposure to light at night is a change in immune function, notably inflammatory responses, and recent research has demonstrated that light at night may detrimentally affect the immune system [18]. Thus, in addition to investigating the influence of melatonin and circadian disruption as mechanisms contributing to the maladaptive affects of light at night, characterization of the inflammatory response is also warranted.

One important population that is often neglected when considering light at night is patients in hospitals. While multiple epidemiological studies have been conducted on nurses, there are no studies on the impact of light at night on the patients with whom they work. Many in-patients are already at high risk of increased inflammation and disrupted physiology, which may be exacerbated by light at night.

Preventing the general population from excessive exposure to light at night can be achieved with relatively low-cost manipulations, such as using curtains to block out street lights, turning off hallway lights, and removing all light sources, including televisions and computers, from bedrooms. However, these methods do not prevent the extension of daytime hours that many of us experience, but by no means do we recommend that everyone go to bed at sunset. Rather, it may be important for people to try to keep a consistent schedule and avoid rapid shifts in their waking hours. This is often unavoidable in shift-working populations, and there are ongoing studies currently comparing visual aids that may alleviate some of the maladaptive effects of exposure to light at night in shift workers. More specifically, not all lighting has an equal effect; the intrinsically photosensitive retinal ganglion cells that project to the master circadian clock in the brain contain melanopsin and are most responsive to the blue region of the visible spectrum (ranging from 450 to 485 nm), with longer wavelengths of lighting minimally impacting the circadian system. Manipulation of wavelength may prove effective in blocking out some of the light-induced physiological changes. Current research investigating the effectiveness of goggles designed to block out blue wavelength lighting on preventing light-induced melatonin suppression is ongoing. Furthermore, work environments could potentially use lighting sources that emit less blue light, which unfortunately is at odds with the push for energy-saving compact fluorescent bulbs.

Modern society now functions on a 24-hour schedule. Although there are many economic and other societal benefits to such a schedule, there is converging evidence from epidemiological and experimental work that light at night has unintended, maladaptive consequences. In many ways, this field of study is just beginning; further characterization of the impact of light at night is needed along with effective interventions to ameliorate the unintended negative effects of light at night on health.

The entire study, the effect of exposure to light at night can be read at this link.

Educational materials of VŠCHT

Biofyzika – Ústav fyziky a měřicí techniky, VŠCHT PRAHA

Fotorecepce

I v oku jsou molekulární akceptory energie – pigmenty. Příjem a zpracování informace o
vnějším světě označujeme jako vidění. Zprostředkovávají nám ho fotony viditelného světla
(elektromagnetické záření o λ = 380-780 nm). Jedná se o fyzikálně-fyziologicko-psychologický
proces, zpracovávaný zrakovým analyzátorem – okem, v němž obraz vnějšího světa
vzniká optickou a fotochemickou cestou. K tomu abychom tento obraz vnímali, je informace
z oka přenášena nervovými buňkami (optickými drahami) do zrakového centra mozku, kde
jsou akční potenciály zpracovány.

…….

Celou studii si můžete přečíst zde.

2007 study

Richard G. Stevens, David E. Blask, George C. Brainard, Johnni Hansen, Steven W. Lockley, Ignacio Provencio, Mark S. Rea, Leslie Reinlib

abstract:

Light, including artificial light, has a range of effects on human physiology and behavior and can therefore alter human physiology when inappropriately timed. One example of potential light-induced disruption is the effect of light on circadian organization, including the production of several hormone rhythms. Changes in light–dark exposure (e.g., by nonday occupation or transmeridian travel) shift the timing of the circadian system such that internal rhythms can become desynchronized from both the external environment and internally with each other, impairing our ability to sleep and wake at the appropriate times and compromising physiologic and metabolic processes. Light can also have direct acute effects on neuroendocrine systems, for example, in suppressing melatonin synthesis or elevating cortisol production that may have untoward long-term consequences. For these reasons, the National Institute of Environmental Health Sciences convened a workshop of a diverse group of scientists to consider how best to conduct research on possible connections between lighting and health. According to the participants in the workshop, there are three broad areas of research effort that need to be addressed. First are the basic biophysical and molecular genetic mechanisms for phototransduction for circadian, neuroendocrine, and neurobehavioral regulation. Second are the possible physiologic consequences of disrupting these circadian regulatory processes such as on hormone production, particularly melatonin, and normal and neoplastic tissue growth dynamics. Third are effects of light-induced physiologic disruption on disease occurrence and prognosis, and how prevention and treatment could be improved by application of this knowledge.

Humans have evolved over millions of years and adapted to a solar day of approximately 12 hr of light and 12 hr of dark, latitude and season permitting. Our ability to artificially light the night began about 250,000 years ago when we discovered how to use fire. Candles were introduced about 5,000 years ago, and gas street lighting was possible beginning in the mid-1700s. However, only in the last 120 years has environmental illumination begun to change on a pervasive scale for the masses of people through the introduction of electric lighting. One of the defining features of the built environment in the modern world is this artificial lighting. Electricity has made it possible to light the inside of large buildings and light the night for work, recreation, and security. The benefits of this lighting are obvious and enormous. It has become apparent, however, that although of obvious benefit, it may not be completely innocuous.

Keywords: breast cancer, circadian rhythms, clock genes, lighting, melatonin, phototransduction, pineal gland

……

Summary:

One of the defining characteristics of life in the modern world is the altered patterns of light and dark in the built environment made possible by use of electric power. A rapidly growing and very exciting body of basic science is uncovering the mechanisms for phototransduction in the retina for environmental control of circadian and other neurobehavioral responses and the makeup and functioning of the clock physiology that exert genetic control of the endogenous rhythms. It is beginning to be realized by the larger scientific community that maintenance of these circadian rhythms is important to health and well-being. Our challenge for the future is to integrate the basic science with studies in experimental animals and clinical and epidemiologic research to advance our understanding of the impact of circadian disruption from lighting, and what then can be done to minimize or eliminate the adverse consequences for human health.
The entire study can be read on this page.

2007 study

Faculty of Health and Medical Sciences, Human Chronobiology Group, University of Surrey, Guildford, Surrey, UK

The relative contribution of rods, cones, and melanopsin to non-image-forming (NIF) responses under light conditions differing in irradiance, duration, and spectral composition remains to be determined in humans. NIF responses to a polychromatic light source may be very different to that predicted from the published human action spectra data, which have utilized narrow band monochromatic light and demonstrated short wavelength sensitivity. To test the hypothesis that only melanopsin is driving NIF responses in humans, monochromatic blue light (lambda(max) 479 nm) was matched with polychromatic white light for total melanopsin-stimulating photons at three light intensities. The ability of these light conditions to suppress nocturnal melatonin production was assessed. A within-subject crossover design was used to investigate the suppressive effect of nocturnal light on melatonin production in a group of diurnally active young male subjects aged 18-35 yrs (24.9+/-3.8 yrs; mean+/-SD; n=11). A 30 min light pulse, individually timed to occur on the rising phase of the melatonin rhythm, was administered between 23:30 and 01:30 h. Regularly timed blood samples were taken for measurement of plasma melatonin. Repeated measures two-way ANOVA, with irradiance and light condition as factors, was used for statistical analysis (n=9 analyzed). There was a significant effect of both light intensity (p<0.001) and light condition (p<0.01). Polychromatic light was more effective at suppressing nocturnal melatonin than monochromatic blue light matched for melanopsin stimulation, implying that the melatonin suppression response is not solely driven by melanopsin. The findings suggest a stimulatory effect of the additional wavelengths of light present in the polychromatic light, which could be mediated via the stimulation of cone photopigments and/or melanopsin regeneration. The results of this study may be relevant to designing the spectral composition of polychromatic lights for use in the home and workplace, as well as in the treatment of circadian rhythm disorders.
The study can be found at this link.