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Journal ArticleDOI

Light-at-night, circadian disruption and breast cancer: assessment of existing evidence

01 Aug 2009-International Journal of Epidemiology (Oxford University Press)-Vol. 38, Iss: 4, pp 963-970

TL;DR: If a consensus eventually emerges that LAN does increase risk, then the mechanisms for the effect are important to elucidate for intervention and mitigation and will provide for the development of lighting technologies at home and at work that minimize circadian disruption, while maintaining visual efficiency and aesthetics.

AbstractBackground Breast cancer incidence is increasing globally for largely unknown reasons. The possibility that a portion of the breast cancer burden might be explained by the introduction and increasing use of electricity to light the night was suggested >20 years ago. Methods The theory is based on nocturnal light-induced disruption of circadian rhythms, notably reduction of melatonin synthesis. It has formed the basis for a series of predictions including that non-day shift work would increase risk, blind women would be at lower risk, long sleep duration would lower risk and community nighttime light level would co-distribute with breast cancer incidence on the population level. Results Accumulation of epidemiological evidence has accelerated in recent years, reflected in an International Agency for Research on Cancer (IARC) classification of shift work as a probable human carcinogen (2A). There is also a strong rodent model in support of the light-at-night (LAN) idea. Conclusion If a consensus eventually emerges that LAN does increase risk, then the mechanisms for the effect are important to elucidate for intervention and mitigation. The basic understanding of phototransduction for the circadian system, and of the molecular genetics of circadian rhythm generation are both advancing rapidly, and will provide for the development of lighting technologies at home and at work that minimize circadian disruption, while maintaining visual efficiency and aesthetics. In the interim, there are strategies now available to reduce the potential for circadian disruption, which include extending the daily dark period, appreciate nocturnal awakening in the dark, using dim red light for nighttime necessities, and unless recommended by a physician, not taking melatonin tablets.

Topics: Circadian rhythm (52%), Shift work (52%)

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Citations
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Journal ArticleDOI
TL;DR: Control of electron flux, prevention of bottlenecks in the respiratory chain and electron leakage contribute to the avoidance of damage by free radicals and seem to be important in neuroprotection, inflammatory diseases and, presumably, aging.
Abstract: Melatonin, the neurohormone of the pineal gland, is also produced by various other tissues and cells. It acts via G protein-coupled receptors expressed in various areas of the central nervous system and in peripheral tissues. Parallel signaling mechanisms lead to cell-specific control and recruitment of downstream factors, including various kinases, transcription factors and ion channels. Additional actions via nuclear receptors and other binding sites are likely. By virtue of high receptor density in the circadian pacemaker, melatonin is involved in the phasing of circadian rhythms and sleep promotion. Additionally, it exerts effects on peripheral oscillators, including phase coupling of parallel cellular clocks based on alternate use of core oscillator proteins. Direct central and peripheral actions concern the up- or downregulation of various proteins, among which inducible and neuronal NO synthases seem to be of particular importance for antagonizing inflammation and excitotoxicity. The methoxyindole is also synthesized in several peripheral tissues, so that the total content of tissue melatonin exceeds by far the amounts in the circulation. Emerging fields in melatonin research concern receptor polymorphism in relation to various diseases, the control of sleep, the metabolic syndrome, weight control, diabetes type 2 and insulin resistance, and mitochondrial effects. Control of electron flux, prevention of bottlenecks in the respiratory chain and electron leakage contribute to the avoidance of damage by free radicals and seem to be important in neuroprotection, inflammatory diseases and, presumably, aging. Newly discovered influences on sirtuins and downstream factors indicate that melatonin has a role in mitochondrial biogenesis.

619 citations


Cites background from "Light-at-night, circadian disruptio..."

  • ...The precise mechanisms of cancer prevention remain to be elucidated (Stevens, 2009)....

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Journal ArticleDOI
TL;DR: A framework that focuses on the cross‐factoring of the ways in which artificial lighting alters natural light regimes (spatially, temporally, and spectrally), and the ways that light influences biological systems, particularly the distinction between light as a resource and light as an information source is proposed.
Abstract: The ecological impacts of nighttime light pollution have been a longstanding source of concern, accentuated by realized and projected growth in electrical lighting. As human communities and lighting technologies develop, artificial light increasingly modifies natural light regimes by encroaching on dark refuges in space, in time, and across wavelengths. A wide variety of ecological implications of artificial light have been identified. However, the primary research to date is largely focused on the disruptive influence of nighttime light on higher vertebrates, and while comprehensive reviews have been compiled along taxonomic lines and within specific research domains, the subject is in need of synthesis within a common mechanistic framework. Here we propose such a framework that focuses on the cross-factoring of the ways in which artificial lighting alters natural light regimes (spatially, temporally, and spectrally), and the ways in which light influences biological systems, particularly the distinction between light as a resource and light as an information source. We review the evidence for each of the combinations of this cross-factoring. As artificial lighting alters natural patterns of light in space, time and across wavelengths, natural patterns of resource use and information flows may be disrupted, with downstream effects to the structure and function of ecosystems. This review highlights: (i) the potential influence of nighttime lighting at all levels of biological organisation (from cell to ecosystem); (ii) the significant impact that even low levels of nighttime light pollution can have; and (iii) the existence of major research gaps, particularly in terms of the impacts of light at population and ecosystem levels, identification of intensity thresholds, and the spatial extent of impacts in the vicinity of artificial lights.

560 citations


Cites background from "Light-at-night, circadian disruptio..."

  • ...Exposure to light at night has been shown to disrupt the circadian cycle of hormone production in humans, particularly melatonin, which has been linked to an increase in cancer risk in shift-workers (Stevens, 1987, 2009; Megdal et al., 2005; Reiter et al., 2011)....

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Journal ArticleDOI
TL;DR: Findings on shift work, in relation to risks of CVD, metabolic syndrome and diabetes are also suggestive but not conclusive for an adverse relationship, making it difficult to draw general conclusions.
Abstract: Background Shift work, including night work, has been hypothesized to increase the risk of chronic diseases, including cancer, cardiovascular disease (CVD), metabolic syndrome and diabetes. Recent reviews of evidence relating to these hypotheses have focussed on specific diseases or potential mechanisms, but no general summary of the current data on shift work and chronic disease has been published. Methods Systematic and critical reviews and recent original studies indexed in PubMed prior to 31 December 2009 were retrieved, aided by manual searches of reference lists. The main conclusions from reviews and principle results from recent studies are presented in text and tables. Results Published evidence is suggestive but not conclusive for an adverse association between night work and breast cancer but limited and inconsistent for cancers at other sites and all cancers combined. Findings on shift work, in relation to risks of CVD, metabolic syndrome and diabetes are also suggestive but not conclusive for an adverse relationship. Conclusions Heterogeneity of study exposures and outcomes and emphasis on positive but non-significant results make it difficult to draw general conclusions. Further data are needed for additional disease endpoints and study populations.

462 citations


Cites background from "Light-at-night, circadian disruptio..."

  • ...responsible for the rise in breast cancer incidence seen in the industrialized world [3]....

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Journal ArticleDOI
TL;DR: The amount of pollution is strongly dependent on the spectral characteristics of the lamps, with the more environmentally friendly lamps being low pressure sodium, followed by high pressure sodium and most polluting are the lamps with a strong blue emission, like Metal Halide and white LEDs.
Abstract: Light pollution is one of the most rapidly increasing types of environmental degradation. Its levels have been growing exponentially over the natural nocturnal lighting levels provided by starlight and moonlight. To limit this pollution several effective practices have been defined: the use of shielding on lighting fixture to prevent direct upward light, particularly at low angles above the horizon; no over lighting, i.e. avoid using higher lighting levels than strictly needed for the task, constraining illumination to the area where it is needed and the time it will be used. Nevertheless, even after the best control of the light distribution is reached and when the proper quantity of light is used, some upward light emission remains, due to reflections from the lit surfaces and atmospheric scatter. The environmental impact of this "residual light pollution", cannot be neglected and should be limited too. Here we propose a new way to limit the effects of this residual light pollution on wildlife, human health and stellar visibility. We performed analysis of the spectra of common types of lamps for external use, including the new LEDs. We evaluated their emissions relative to the spectral response functions of human eye photoreceptors, in the photopic, scotopic and the 'meltopic' melatonin suppressing bands. We found that the amount of pollution is strongly dependent on the spectral characteristics of the lamps, with the more environ- mentally friendly lamps being low pressure sodium, followed by high pressure sodium. Most polluting are the lamps with a strong blue emission, like Metal Halide and white LEDs. Migration from the now widely used sodium lamps to white lamps (MH and LEDs) would produce an increase of pollution in the scotopic and melatonin suppression bands of more than five times the present levels, supposing the same photopic installed flux. This increase will exacerbate known and possible unknown effects of light pollution on human health, environment and on visual perception of the Universe by humans. We present quantitative criteria to evaluate the lamps based on their spectral emissions and we suggest regulatory limits for future lighting.

395 citations


Cites background from "Light-at-night, circadian disruptio..."

  • ...As seen, circadian disruption is also induced by light exposure at night and light at night is becoming a public health issue (Pauley, 2004; Stevens, 2009)....

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Journal ArticleDOI
TL;DR: The possible multiple and interconnected cancer-promoting mechanisms as a consequence of shift work are examined, i.e., repeated disruption of the circadian system, pineal hormone melatonin suppression by exposure to light at night, sleep-deprivation-caused impairment of the immune system, plus metabolic changes favoring obesity and generation of proinflammatory reactive oxygen species.
Abstract: Shift work that includes a nighttime rotation has become an unavoidable attribute of today's 24-h society. The related disruption of the human circadian time organization leads in the short-term to an array of jet-lag-like symptoms, and in the long-run it may contribute to weight gain/obesity, metabolic syndrome/type II diabetes, and cardiovascular disease. Epidemiologic studies also suggest increased cancer risk, especially for breast cancer, in night and rotating female shift workers. If confirmed in more controlled and detailed studies, the carcinogenic effect of night and shift work will constitute additional serious medical, economic, and social problems for a substantial proportion of the working population. Here, we examine the possible multiple and interconnected cancer-promoting mechanisms as a consequence of shift work, i.e., repeated disruption of the circadian system, pineal hormone melatonin suppression by exposure to light at night, sleep-deprivation-caused impairment of the immune system, plus metabolic changes favoring obesity and generation of proinflammatory reactive oxygen species.

346 citations


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