Breast cancer and circadian disruption from electric lighting in the modern world


  • Richard G. Stevens PhD,

    Corresponding author
    1. Professor, Department of Community Medicine, University of Connecticut Health Center, Farmington, CT
    • Corresponding author: Richard G. Stevens, PhD, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-6325;

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  • George C. Brainard PhD,

    1. Professor, Department of Neurology, Thomas Jefferson Medical College, Philadelphia, PA
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  • David E. Blask PhD, MD,

    1. Professor, Department of Structural and Cellular Biology, Tulane University School of Medicine, Tulane University, New Orleans, LA
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  • Steven W. Lockley PhD,

    1. Associate Professor, Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
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  • Mario E. Motta MD

    1. Associate Professor, Department of Medicine, Tufts Medical School, Boston, MA
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  • DISCLOSURES: This work was supported in part by the Institute for Integrative Health to G.C.B. and in part by grant 1R21CA129875 from the National Cancer Institute to D.E.B. This work was also supported by the National Space Biomedical Research Institute through grant NASA NCC 9-58 to G.C.B. and S.W.L. Dr. Brainard reports grants from the Institute for Integrative Health and the National Space Biomedical Research Institute during the conduct of the study; an unrestricted gift from Philips Lighting to his institution; and nonfinancial support from Lutron, Lighting Sciences Group, and Litebook outside the submitted work. In addition, Dr. Brainard has a patent titled “Portable Light Unit for Stimulating the Neuroendocrine System and Achieving Phototherapy for Depression” (Canada/Japan) licensed to G.C. Brainard; a patent titled “Photoreceptor System for Melatonin Regulation and Phototherapy” issued to G.C. Brainard and G. Glickman; a patent titled “Photoreceptor System for Melatonin Regulation and Phototherapy” pending to G.C. Brainard and G. Glickman; and a patent titled “Method for Modifying or Resetting the Circadian Cycle Using Short Wavelength Light” pending to C.A. Czeisler, G.C. Brainard, S.W. Lockley, and R.E. Kronauer. He reports speaking honoraria and/or travel expenses received in 2011 from Illuminating Engineers Society, National Aeronautics and Space Administration Behavioral Health and Performance Working Group (NASA BHPWG), and Abington Hospital; in 2012 from Illuminating Engineering Society, Parsons New School, Noche Zero, University of Michigan, National Space Biomedical Institute, AlCon, Longwood Gardens, and NASA BHPWG; and in 2013 from Illuminating Engineering Society, Philips Lighting, International Association of Lighting Design, and the Association of Research and Enlightenment. Dr. Lockley reports consultancy fees from Wyle Integrated Science and Engineering, Naturebright, Headwaters, PlanLED, Blackrock, Cowen & Company, Endurant Capital Management, Fidelity, Frankel Group, Impax Labs, Kearney Venture Partners, Lazard Capital Markets, New Horizon Capital, Perceptive Advisors, Polar Capital, ResearchWorks Inc., and Wyvern Funds; fees as an expert witness from Armstrong Management Lawyers, Rothstein Law Firm, Hicks Morley Hamilton Steward Storie LLP, and Cox & Palmer; grants to his institution from Philips Lighting and Biological Illuminations LLC; honorarium for seminar from Harvard University; patent through his institution for short-wavelength light; book royalties from Oxford University Press; payment from MediCom Worldwide Inc. for developing educational presentations; compensation for travel/accommodation/meeting expenses from Wyle Integrated Science and Engineering, Ontario Association of Fire Chiefs, the Eighth International Conference on Managing Fatigue, Rio Tinto, New England College of Occupational and Educational Medicine (NECOEM), the Connecticut Business & Industry Association Health and Safety Conference, Emergency Services Steering Committee, Cantifix, and the Illuminating Engineering Society Conference; and unrestricted gifts of lighting equipment from Philips Lighting, Bionetics Corporation, and Biological Illuminations LLC.


Breast cancer is the leading cause of cancer death among women worldwide, and there is only a limited explanation of why. Risk is highest in the most industrialized countries but also is rising rapidly in the developing world. Known risk factors account for only a portion of the incidence in the high-risk populations, and there has been considerable speculation and many false leads on other possibly major determinants of risk, such as dietary fat. A hallmark of industrialization is the increasing use of electricity to light the night, both within the home and without. It has only recently become clear that this evolutionarily new and, thereby, unnatural exposure can disrupt human circadian rhythmicity, of which three salient features are melatonin production, sleep, and the circadian clock. A convergence of research in cells, rodents, and humans suggests that the health consequences of circadian disruption may be substantial. An innovative experimental model has shown that light at night markedly increases the growth of human breast cancer xenografts in rats. In humans, the theory that light exposure at night increases breast cancer risk leads to specific predictions that are being tested epidemiologically: evidence has accumulated on risk in shift workers, risk in blind women, and the impact of sleep duration on risk. If electric light at night does explain a portion of the breast cancer burden, then there are practical interventions that can be implemented, including more selective use of light and the adoption of recent advances in lighting technology and application. CA Cancer J Clin 2014;64:207–218. © 2013 American Cancer Society.