Light At Night (LAN) and Health
Skykeepers founded
September 1, 1999
This page is under construction
This page is dedicated to a survey of web links, reports, studies, and news stories relating to Light at Night (LAN), melatonin, circadian rhythm, action spectrum, etc. and human health.

Introduction -
Light Pollution and Light at Night (LAN) is now a true public health issue.  In 2007 the World Health Organization (WHO) (through the IARC)  listed shift work as a "probable carcinogen".  
We are as part of the whole of Nature as is every other living thing, and that we have eons-old melatonin rhythms just like algae.  We are beings who, up until 1879 and Edison's light bulb, lived within a natural light-dark cycle. Our optimum physiology depends on that.  Today, because we're born into a world where, in the name of "safety", darkness has been turned nearly into daylight, we don't appreciate the connections to our evolutionary past. We've become a 24-7 society that is getting sicker due in part to disrupted sleep and melatonin rhythms.
With the introduction of Mercury Vapor (MV), Florescent, Metal Halide (MV) and now some LED light sources into our society and environment an even more intrusive and destructive force has been unleashed.  It is white light which contains a considerable quantity of blue light, the same blue light that controls our circadian rhythm.   While it is true blue light is important and natural during the day, it totally unnatural and disruptive at night.
Much of this page references, links to, or is based on the work of  Blask, Brainard, Reiter, Stevens and many others.

Related Internal Links -
Echolocical Light Pollution -  
Danger Blue Light Ahead - under development or sub section of this page.
Danger LED Light Ahead - under development
Photobiology and Pathology -
Lighting for the human circadian clock: recent research indicates that lighting has become a public health issue ( .pdf  167k ),  
Dr.  Stephen M. Pauley,  Medical Hypotheses (2004) 63, 588 596,
Summary   The hypothesis that the suppression of melatonin (MLT) by exposure to light at night (LAN) may be one reason for the higher rates of breast and colorectal cancers in the developed world deserves more attention. The literature supports raising this subject for awareness as a growing public health issue. Evidence now exists that indirectly links exposures to LAN to human breast and colorectal cancers in shift workers. The hypothesis begs an even larger question: has medical science overlooked the suppression of MLT by LAN as a contributor to the overall incidence of cancer?  ...

Light at night and working the graveyard shift linked to increased risk of breast cancer 16 OCT 2001

Artificial light at night stimulates breast cancer growth in laboratory mice, NIH/National Institute of Environmental Health Sciences , 19-Dec-2005
Results from a new study in laboratory mice show that nighttime exposure to artificial light stimulated the growth of human breast tumors by suppressing the levels of a key hormone called melatonin. The study also showed that extended periods of nighttime darkness greatly slowed the growth of these tumors.   The study results might explain why female night shift workers have a higher rate of breast cancer. It also offers a promising new explanation for the epidemic rise in breast cancer incidence in industrialized countries like the United States.  ...

State of the Evidence What - is the Connection Between.... (.pdf)  (see Melatonin) 2006 update. 
... Research has shown that exposure to light at night also decreases melatonin levels. This finding led to the hypothesis that night-shift work (working
at night in a lighted environment) may increase the risk of breast cancer by lowering melatonin levels. Although this hypothesis remains controversial,
at least three studies suggest a link between night-shift work and increased risk of breast cancer.356,357,358 A recent prospective study from
Harvard indicated that higher melatonin levels were associated with a lower risk of breast cancer.359 ...

Hormone Melatonin Slows Breast Cancer,  Bright Light at Night Linked to Increased Risk - WebMD

Night-Shift Work and Risk of Colorectal Cancer in the Nurses’ Health Study JNCI,, Vol. 95, No. 11, 825-828, June 4, 2003
...Exposure to light at night suppresses the physiologic production of melatonin, a hormone that has antiproliferative effects on intestinal cancers. Although observational studies have associated night-shift work with an increased risk of breast cancer, the effect of night-shift work on the risk of other cancers is not known. ...   These data suggest that working a rotating night shift at least three nights per month for 15 or more years may increase the risk of colorectal cancer in women.  

Light, Endocrine Systems and Cancer A Meeting Report (.pdf), International Symposium Light, Endocrine Systems and Cancer held May 2-3, 2002
Light. pollution at night reduces melatonin synthesis and secretion and hence .... suppression and cancer progression” results were presented on the ...

The potential of melatonin in reducing morbidity–mortality after craniocerebral trauma,   M.D. Maldonado,  R. J. Reiter and others
Melatonin reduces the toxicity... Finally, melatonin crosses the blood–brain barrier and reduces contusion volume and stabilizes cellular membranes preventing vasospasm and apoptosis of endothelial cells that occurs as a result of CCT.
Journal of Pineal Research, Volume 42 Issue 1 Page 1-11, January 2007

Towards rational and evidence-based use of melatonin in prostate cancer prevention and treatment,   Stephen Y. W. Shiu
The rational use of melatonin in prostate cancer prevention, stabilization of clinically localized favourable-risk prostate cancer and palliative treatment of advanced or metastatic tumour is discussed within the context of the molecular pathogenesis of the disease.
Journal of Pineal Research,  Volume 43 Issue 1 Page 1-9, August 2007

Signaling mechanisms of melatonin in antiproliferation of hormone-refractory 22Rv1 human prostate cancer cells: implications for prostate cancer chemoprevention,   Chun W. Tam, Chi W. Mo, Kwok-Ming Yao, Stephen Y. W. Shiu
"Taken together with the known molecular mechanisms of prostate cancer progression and transition to androgen independence, our data provide strong support for melatonin to be a promising small-molecule useful for prostate cancer primary prevention and secondary prevention of the development and progression of hormone refractoriness."
Journal of Pineal Research,  Volume 42 Issue 2 Page 191-202, March 2007

Melatonin-Depleted Blood from Premenopausal Women Exposed to Light at Night Stimulates Growth of Human Breast Cancer Xenografts in Nude Rats, David E. Blask, PhD, MD, George C. Brainard, Ph.D., others,  [Cancer Research 65, 11174-11184, December 1, 2005]  "The increased breast cancer risk in female night shift workers has been postulated to result from the suppression of pineal melatonin production by exposure to light at night. Exposure of rats bearing rat hepatomas or human breast cancer xenografts to increasing intensities of white fluorescent light during each 12-hour dark phase (0-345 µW/cm2) resulted in a dose-dependent suppression of nocturnal melatonin blood levels and a stimulation of tumor growth and linoleic acid uptake/metabolism to the mitogenic molecule 13-hydroxyoctadecadienoic acid. " ...
Requests for reprints: David E. Blask, Laboratory of Chrono-Neuroendocrine Oncology, Bassett Research Institute, The Mary Imogene Bassett Hospital, Cooperstown, NY 13326. Phone: 607-547-367Light At Night (LAN) and HealthLight At Night (LAN) and HealthLight At Night (LAN) and HealthLight At Night (LAN) and Health7; Fax: 607-547-3061; E-mail: david.blask ((at))

News Stories in the Popular Press --

Graveyard Shift Work Linked to Cancer,
FoxNews (AP Story), Friday, November 30, 2007
Like UV rays and diesel exhaust fumes, working the graveyard shift will soon be listed as a "probable" cause of cancer.
It is a surprising step validating a concept once considered wacky. And it is based on research that finds higher rates of breast and prostate cancer among women and men whose work day starts after dark.
Next month, the International Agency for Research on Cancer, the cancer arm of the World Health Organization, will add overnight shift work as a probable carcinogen.
The higher cancer rates don't prove working overnight can cause cancer. There may be other factors common among graveyard shift workers that raise their risk for cancer.
However, scientists suspect that overnight work is dangerous because it disrupts the circadian rhythm, the body's biological clock. The hormone melatonin, which can suppress tumor development, is normally produced at night.   ...

Night shift a 'probable' carcinogen, The Boston Globe (AP story), By Associated Press, November 30, 2007
Prostate, breast cancers likelier among those working overnight ...
Among the first to spot the night shift-cancer connection was Richard Stevens, a cancer epidemiologist and professor at the University of Connecticut Health Center. In 1987, Stevens published a paper suggesting a link between light at night and breast cancer.
Back then, he was trying to figure out why breast cancer incidence suddenly shot up starting in the 1930s in industrialized societies, where night work was considered a hallmark of progress. Most scientists were bewildered by his proposal.
But in recent years, several studies have found that women working at night over many years were indeed more prone to breast cancer. Also, animals that have their light-dark schedules switched develop more cancerous tumors and die earlier.  ...
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Seeing the Light of Day, Washington Post
Artificial Illumination Can Affect More Than Your Mental Health. As Daylight Saving Time Comes to an End, What Happens to Our Internal Clocks?
Oh, the light! The autumn light! Is there anything more glorious than an October day, awash in the sun's low-slung amber rays? ...
Much more than mental health is at stake. Women who work at night, out of sync with the light, have recently been shown to have higher rates of breast cancer -- so much so that an arm of the World Health Organization will announce in December that it is classifying shift work as a "probable carcinogen."
That will put the night shift in the same health-risk category as exposure to such toxic chemicals as trichloroethylene, vinyl chloride and polychlorinated biphenyls (PCBs).

Light 'risk' to premature babies, BBC News, 21 August 2006, 09:24 GMT 10:24 UK,  "Constant exposure to artificial hospital lighting may damage the development of premature babies' biological clocks, research suggests.  Tests showed exposing baby mice to constant light keeps the master biological clock in their brains from developing properly.  ...

Study: Harsh Lighting May Damage Embryos, San Jose Mercury News (AP News)  - Aug 14, 2007   ( Bad Link - link has changed)
"Sunlight and cool-white fluorescent lights caused the most damage to mice embryos in the study, even when exposure was limited to a few minutes, said Dr. Ryuzo Yanagimachi, a retired University of Hawaii researcher known for his expertise in reproductive biology."
Cool-white fluorescents, which are blue-white in appearance, are commonly used in office environments.
Warm-white lights, which are yellow-white in color and popular in residential settings, resulted in "far more" eggs developing into babies, Yanagimachi said.    "We found that warm-white light is less damaging," Yanagimachi said.  ...    
"People do not pay much attention to light as a negative environmental factor," he said.
Alternate URL=,4670,LightEmbryos,00.html, FOXNEWS.COM Science, Tuesday, August 14, 2007
Alternate URL=,  First Coast News Health
Alternate URL=, Discovery Channel News

Turning Out the Lights - the dangers of a bright night are becoming more apparent, US NEWS & World Reports, By Ben Harder, Posted March 14, 2008
... "People who are working while others are stargazing may face the greatest risks. Hormonal disturbances triggered by nighttime exposure to white or bluish light can disrupt circadian rhythms and fuel the growth of tumors, experiments show. Two decades of research indicate that women who work night shifts have unusually high rates of breast cancer, and some data suggest a parallel effect on male workers' prostate cancer rates. Last December, a unit of the World Health Organization deemed shift work a probable human carcinogen." ...

Scientists Discuss Possible Dangers of Nighttime Light Kansas City infoZine, MO - Feb 23, 2007
Are the streetlights and security lights the Western world takes for granted causing breast cancer, killing sea turtles and blocking views of the constellations? ...  George C. Brainard, a professor of neurology and pharmacology at Jefferson Medical College in Philadelphia, said some research points to a rise in breast cancer for women living in industrialized countries.
The bombardment of light may prevent the brain from producing melatonin, a hormone some researchers think combats cancer, Brainard said. ...
"Melatonin follows the pattern of dark time," he added.More than 100 scientists, lighting technicians and government workers registered for the two-day conference hosted by the Carnegie Institution, a non-profit research center. ...
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Other Related Links -
Danger LED Light Ahead - saved links
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U.S. Bank Tower’s light show to debut in Sacramento, By Jon Ortiz, Published 12:00 am PDT Monday, April 28, 2008 (Print Ver.)
Extra LEDs will add to Sacramento building's artistic lighting, By Jon Ortiz, Published 12:00 am PDT Saturday, May 24, 2008  (Print Ver.)
Giant LED screen is sign of new times at Downtown Plaza, By Bob Shallit ,  Published 12:00 am PDT Wednesday, June 4, 2008 (Print Ver.)  / Lighting Science Group / LED Effects

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18 JUN 2008
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