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.
Abstract: Background 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.
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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.
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...The precise mechanisms of cancer prevention remain to be elucidated (Stevens, 2009)....
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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.
706 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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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.
514 citations
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...responsible for the rise in breast cancer incidence seen in the industrialized world [3]....
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...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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TL;DR: Understanding the daily rhythm of the immune system could have implications for vaccinations and how the authors manage infectious and inflammatory diseases.
424 citations
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...It has also been concluded that ‘shift work that involves circadian disruption is probably carcinogenic to humans’ (Straif et al., 2007) and can lead to higher incidence of cardiovascular disease and obesity (Karlsson et al., 2001; Stevens, 2009)....
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References
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TL;DR: In this paper, the authors evaluated and critically analyzed all randomized clinical trials (RCTs) of ''alternative cancer cures'' (ACCs) for breast cancer and found that in most cases their methodological quality was low, with only two RCTs scoring ''4'' and four RCTS scoring ''3'' out of 5 possible points for methodological quality.
Abstract: The objectives of this study was to evaluate and critically analyze all randomized clinical trials (RCTs) of ''alternative cancer cures'' (ACCs) for breast cancer. The electronic databases Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, Allied and Complementary Medicine, Scirus, BIOSIS, CancerLit and CINAHL and for ongoing trials the MetaRegister at http://www.controlled-trials.com/ and the National Research Register at http://www.update-software.com/national/ were searched from their inception. Bibliographies of located studies were scanned. Unpublished or ongoing trials were identified through correspondence with experts in the field. Our own files were hand searched for further RCTs. Review methods included a systematic review of RCTs involving breast cancer patients treated with ACCs, survival, parameters indicative of tumor burden, disease progression, cancer recurrence, and cancer cure. Results were tabulated and summarized. Thirteen RCTs met the inclusion criteria. In most cases their methodological quality is low, with only two RCTs scoring ''4'' and four RCTs scoring ''3'' out of 5 possible points for methodological quality. The treatments tested included various methods of psychosocial support such as group support therapy, cognitive behavioral therapy cognitive existential group therapy, a combination of muscle relaxation training and guided imagery, the Chinese herbal remedy Shi Quan Da Bu Tang, thymus extract, transfer factor, melatonin, and factor AF2. Encouraging but not fully convincing results emerged for melatonin.
37 citations
TL;DR: In this paper, the melatonin hypothesis states that excess exposure to environmental light may contribute to breast cancer risks via impaired pineal secretion of melatonin and a corollary, not considered previously, is that a net annual increase in oncostatic melatonin would be expected in persons who experience a light deficit during extended winter darkness periods; thus, hormone-dependent cancers should occur less frequently in people who reside north, rather than south, of the Arctic circle.
35 citations
TL;DR: A relatively high physical activity and a diet rich in fish may in part explain the low cancer incidence of the Sami population in North Norway.
Abstract: The Sami population in North Norway constitutes an ethnic minority with a lifestyle that diverges from that of the rest of the population. A cohort of 19 801 people of Sami origin was followed for cancer incidence over the period 1970-1997 by the Norwegian Cancer Registry. Among the Sami 1340 cases of cancer were observed versus 1658.2 expected, based on a regional reference population. For both sexes a significantly decreased incidence of colon cancer was observed. The standardized incidence ratio (SIR) for men was 0.50 (95% confidence interval (CI) 0.34-0.71) and for women 0.62 (95% CI 0.43-0.85). Low SIRs were observed for lung cancer: 0.63 (95% CI 0.51-0.77) and 0.60 (95% CI 0.37-0.91), for men and women, respectively. Men of Sami ancestry had a decreased risk of prostate cancer: SIR 0.57 (95% CI 0.45-0.71). Among women 127 cases of breast cancer were observed versus 149.6 expected. A relatively high physical activity and a diet rich in fish may in part explain the low cancer incidence. Some Sami were exposed to radioactivity as a result of their diet based on reindeer products. Adverse effects on their cancer incidence were not observed.
35 citations
TL;DR: This book focuses on reports about knowledge and concepts of action of light in healthy and sick persons in medical science since Hippocratkv, the ancient Arabian physicians up to the contemporaries of the author, and references of knowledge of circadian and seasonal rhythms in living nature, especially in the normal and sick human being who seems to be dependent on daily change of light and darkness.
Abstract: The court-bookqeller of Osnabriick (a small residence town in northwestern Germany) published a book in 1799 entitled Essay of Q History of the Light Concerned with its Influence on the Whole Nature andWithout the Sense of Sight Especially on the Human Body by Johann Christof Ebermaier.l In this book our attention is called to (1) reports about knowledge and concepts of action of light in healthy and sick persons in medical science since Hippocratkv, the ancient Arabian physicians up to the contemporaries of the author; (2) references of knowledge of circadian and seasonal rhythms in living nature, especially in the normal and sick human being who seems to be dependent on daily change of light and darkness; (3) a thorough overview of photophysiologic concepts of the author and his contemporaries. In the climatic conditions of the Mediterranean region the ancient Arabian physicians seemed to have discovered very early the importance of the circadian chaltge in light and darkness and of its seasonal variation. They were not yet able to divide totally or in part between the action of light or of temperature. The action of light was thought to be transmitted not by the eyes but communicated by the whole body surface. The author a t the end of the eighteenth century came to the same conclusion: Impressed by the activity of plant metabolism just discovered in which oxygen was released (known to be vital for any type of animal life) and the expired carbon dioxide was absorbed, action of light was explained by communication of the whole organism with a “vital atmosphere,” which was thought to result from a chemical Kinding between oxygen and a gaslike, light material. Because in blind people, activity and sleeping periods were the same in regard to normal people, this experience should be evidence for the efficiency of this light-dependent “vital atmosphere,” mostly active by inspiration. Ebermaier mentioned the opinion of Fontana, first published in Berlin in 1787, who stated that light would act only on the retina, but rejected this idea. His observation of the persistence of leaf motion activity in plants under constant temperature conditions and permanent darkness was correct, and his question if there are similar correlations with the periodic activity in animals was remarkable. He gave correct descriptions of circadian rhythms in birth and death, of body temperature in healthy and sick men, of the crisis in numerous diseases in the evening, which is caused by change in
33 citations
TL;DR: It seems likely that the Sami ethnicity carries a reduced cancer incidence level, and although many Sami have been exposed to radioactive fallout from the nuclear weapon tests via their reindeer‐rich diet, this does not seem to affect their cancer risk.
Abstract: The Sami population living in Northern Finland represents a specific genetic background and a way of life that is different from other Finns. A cohort of 2,100 Sami and 4,174 non-Sami people from the 2 northernmost municipalities of Finland on 31 December 1978 was identified from the national Population Register and followed up through the Finnish Cancer Registry for cancer incidence during 1979-1998. There were 111 cancer cases among the Sami, while the expected number based on the average cancer incidence in the Finnish population was 173. Among the non-Sami cohort members, there were 226 cases of cancer vs. 224 expected cases. The Sami had significantly decreased incidence of cancers of the prostate [standardised incidence ratio (SIR) 0.25; 95% confidence interval (CI) 0.08-0.58] and breast (SIR 0.36; 95% CI 0.14-0.73), similarly for both localised and nonlocalised tumours. Low SIRs were also observed for bladder cancer (SIR 0.28; 97% CI 0.03-0.99) basal cell carcinoma of the skin (SIR 0.12; 95% CI 0.03-0.30) and other nonmelanoma skin cancers (SIR 0; 95% CI 0-0.63). In contrast to other subcategories of the Sami, the Skolts, whose lifestyle stems from areas that now belong to Russia, showed a nonreduced overall cancer risk and a significantly elevated risk for stomach cancer (SIR 3.8; 95% CI 1.5-7.8). The low cancer incidence among the other Sami populations in Finland cannot be fully explained by their specific way of life. It seems likely that the Sami ethnicity carries a reduced cancer incidence level. Although many Sami have been exposed to radioactive fallout from the nuclear weapon tests via their reindeer-rich diet, this does not seem to affect their cancer risk.
33 citations