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

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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.