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: The association of NTLI with cardiovascular disease (CVD) risk factors identify NTLi as a potentially important tool for exploring urbanisation-related health and consistent associations of moderate increases in urbanisation levels with important CVD risk factors warrant prevention strategies to curb expected large public health impacts from continued and rapid urbanisation in India.
Abstract: Objectives To explore associations of night-time light intensity (NTLI), a novel proxy for continuous urbanisation levels, with mean systolic blood pressure (SBP), body mass index (BMI), fasting serum low-density lipoprotein (LDL) and fasting plasma glucose (FPG), among adults in early-stage urbanisation in Telangana, South India. Design Cross-sectional analysis of the third wave of the Andhra Pradesh Children and Parents Study cohort. Setting 28 villages representing a continuum of urbanisation levels, ranging from rural settlement to medium-sized town in Telangana, South India. Participants Data were available from 6944 participants, 6236 of whom were eligible after excluding pregnant women, participants younger than 18 years of age and participants missing data for age. Participants were excluded if they did not provide fasting blood samples, had implausible or missing outcome values, were medicated for hypertension or diabetes or had triglyceride levels invalidating derived LDL. The analysis included 5924 participants for BMI, 5752 participants for SBP, 5287 participants for LDL and 5328 participants for FPG. Results Increasing NTLI was positively associated with mean BMI, SBP and LDL but not FPG. Adjusted mean differences across the range of village-level NTLI were 1.0 kg/m2 (95% CI 0.01 to 1.9) for BMI; 4.2 mm Hg (95% CI 1.0 to 7.4) for SBP; 0.3 mmol/L (95% CI −0.01 to 0.7) for LDL; and −0.01 mmol/L (95% CI −0.4 to 0.4) for FPG. Associations of NTLI with BMI and SBP were stronger in older age groups. Conclusion The association of NTLI with cardiovascular disease (CVD) risk factors identify NTLI as a potentially important tool for exploring urbanisation-related health. Consistent associations of moderate increases in urbanisation levels with important CVD risk factors warrant prevention strategies to curb expected large public health impacts from continued and rapid urbanisation in India.
12 citations
TL;DR: The comparative assessment revealed significant differences of objective results and public risk perception, and puts EMF risks into perspective, and highlights the necessity for individual's responsible behavior in terms of prudent avoidance.
Abstract: Comparative health risk assessment of electromagnetic fields (EMFs) has been performed in their entire frequency range from static fields until ionizing radiation. Due to considerable change of physical and biologic interaction and the nature of potential adverse health effects comparison was based on the carcinogenic potential of environmental EMF exposure levels. There was a need for sophisticated discrimination of levels of evidence as well as the available database. Conclusions were based on a synoptic view to results of different scientific approaches such as theoretical and biologic interaction modeling, evidence for accumulative effects, in vitro and in vivo investigations and epidemiologic studies. The comparative assessment revealed significant differences of objective results and public risk perception, and puts EMF risks into perspective. It highlights the necessity for individual's responsible behavior in terms of prudent avoidance. The comparison indicates where risk awareness might merit priority. This is not restricted to the UV range but includes also other exposures such as to nocturnal light or within infrared cabins.
12 citations
TL;DR: A set of configurations is presented to determine optimal electric lighting configuration based on natural light conditions in order to ensure a suitable circadian stimulus and the electric lighting flux threshold for different scenarios, benefiting occupants' health while also ensuring energy conservation.
Abstract: Light, especially daylight, plays a critical role in human health as the main timer for circadian rhythms. Indoor environments usually lack the correct exposure to daylight and are highly dependent on electric lighting, disrupting the circadian rhythm and compromising the health of occupants. The methodology proposed assesses the combination of natural and electric lighting on circadian rhythms for operational environments. The case study chosen examines a 24/7 laboratory area representing an open-plan shift-work area. Several electric lighting scenarios under different sky conditions have been assessed, considering a variable window size and resulting in a spectrum which establishes the indoor circadian regulation performance according to the amount of light perceived. A set of configurations is presented to determine optimal electric lighting configuration based on natural light conditions in order to ensure a suitable circadian stimulus and the electric lighting flux threshold for different scenarios, benefiting occupants’ health while also ensuring energy conservation.
12 citations
TL;DR: Investigation of the effect of exposure to dim light at night when sleeping on functional brain activation during a working-memory tasks revealed less activation in the right inferior frontal gyrus (IFG) after exposure to 10-lux light.
Abstract: The aim of this study was to investigate the effect of exposure to dim light at night (dLAN) when sleeping on functional brain activation during a working-memory tasks. We conducted the brain functional magnetic resonance imaging (fMRI) analysis on 20 healthy male subjects. All participants slept in a polysomnography laboratory without light exposure on the first and second nights and under a dim-light condition of either 5 or 10 lux on the third night. The fMRI scanning was conducted during n-back tasks after second and third nights. Statistical parametric maps revealed less activation in the right inferior frontal gyrus (IFG) after exposure to 10-lux light. The brain activity in the right and left IFG areas decreased more during the 2-back task than during the 1- or 0-back task in the 10-lux group. The exposure to 5-lux light had no significant effect on brain activities. The exposure to dLAN might influence the brain function which is related to the cognition.
12 citations
TL;DR: Evidence is reviewed relevant to the hypothesis that natural selection for shorter sleep time in humans has compromised the efficacy of physiological mechanisms that protect against AD during sleep, and possible long-term side effects of medications that reduce sleep are highlighted.
Abstract: Compared with other primates, humans sleep less and have a much higher prevalence of Alzheimer 's disease (AD) pathology. This article reviews evidence relevant to the hypothesis that natural selection for shorter sleep time in humans has compromised the efficacy of physiological mechanisms that protect against AD during sleep. In particular, the glymphatic system drains interstitial fluid from the brain, removing extra-cellular amyloid beta (eAβ) twice as fast during sleep. In addition, melatonin - a peptide hormone that increases markedly during sleep - is an effective antioxidant that inhibits the polymerization of soluble eAβ into insoluble amyloid fibrils that are associated with AD. Sleep deprivation increases plaque formation and AD, which itself disrupts sleep, potentially creating a positive feedback cycle. These and other physiological benefits of sleep may be compromised by short sleep durations. Our hypothesis highlights possible long-term side effects of medications that reduce sleep, and may lead to potential new strategies for preventing and treating AD.
12 citations
Cites background from "Light-at-night, circadian disruptio..."
...Reduced MEL levels, because of lack of sleep or sleeping with lights on, increases the risk of breast cancer [66], as confirmed in mice [67]....
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