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Lights at night and Prostate Cancer Risks in Men

There are many organizations and web pages out there that strive to collect money from you to find a cure for some cancer. These pages are not one of them. It is the philosophy of this page to help prevent health problems by raising the awareness of a man-made factor that can increase their risk of occurring, of which seems to include certain cases of cancer. Just as there are many different paths that one can take to get to a particular designation, there are many possible sources or factors that can cause errors in our cell's genetic coding that lead to cancer. Understanding those sources and avoiding should be our first step to maintain health. However, light pollution is one factor that is increasingly hard to avoid due to its pervasiveness in society and the fact that it is growing exponentially. It is one factor that we inflict upon each other, near and far. It is one factor that we pay each and every night to make. And it is one factor that anyone can help correct.

Disclaimer: I am not an expert in the fields of biology, neuroscience, endocrinology, or oncology. I am, by training, a physicist. What I'll try to cover here is predominately based on my introductory understanding of articles that I have read. These pages then are a limited and a quite incomplete coverage of the evolution of thought regarding this issue, in what little time I have to devote to it. Whether or not the evidence presented here proves to be true or not, I find it to be of sufficient importance, that I thought that it was a worthy usage of that time. This evolving web page contains a growing collection of papers about the issue. Each of the papers, reviewed here, will have key findings highlighted, and the citations to the paper, with online links if possible, so that you can follow up and corroborate what I understand.

As a quick introduction (or just for those who are impatient), here is a recently covered article in a series about night work on CNN.com. Then, if you want to know what to do to correct this problem from affecting yourself or your neighbors, head over to our Light Pollution Prevention page for ideas and tips.


The science in a nutshell: Researchers are concerned that certain health problems can be caused by a long term decrease in the naturally and nightly occurring hormone melatonin, which is only secreted when it is dark and which regulates our sleep/wake cycles and other hormonal glands. While there are different factors that can prevent melatonin from being made by the pineal gland under our brains, such as its calcification due to old age, this web page has been following the particular factor of light pollution at night. Researchers are finding that exposure to bright nocturnal light decreases the human body's production of melatonin, A decrease in melatonin production has been linked to higher rates of breast cancer in women and higher rates of prostate cancer in men. A bit more details on these steps follows.

Light prevents the production of melatonin through primitive ganglion eye cells in our retinas, which we have recently learned are photosensitive. These photosensitive ganglion eye cells are active at or have a peak sensitivity to particular blue wavelengths which does not match the same peak sensitivities of the retinal rod or cone cells. Rod and cone cells are the same retinal cells which you may remember learning about in biology class. While certain cones and rods can see this same spectral region, they just don't react to it as strongly as the ganglion cells do. So blue light, just like blue daytime skies, triggers these ganglion cells, and that makes blue light is our zietgeber (time-giver). These cells send this information to our brain's suprachiasmatic nuclei (SCN), which is a collection of brain cells that is the center of our biological clocks or our circadian system. The SCN turns off the pineal gland, a small endocrine organ that lies just under our brains. However, when it is dark, the ganglion cells do not detect blue light, so the SCN lets the pineal gland produce its hormone melatonin. This melatonin is the chemical message that is released to our body in the blood which causes/activates certain health inducing activities.

Once in the blood, melatonin can not only suppress cancer cell growth or even cause cancer cell death, it also reaches other hormone producing glands, such as the ovaries in women and the pituitary gland, and stops the production of their hormones. The hormones that come from these glands in women are estrogen, progesterone, follicle stimulating hormone (F.S.H.), and the luteinizing hormone (L.H.), can cause rapid breast tissue cell growth. It is the cellular growth and turnover can can allow errors to occur in their genetic coding, which can lead to cancer. Ever greater growth and turnover means more frequent chances for coding errors, and so, greater chances of cancer.

Also, melatonin has been found to absorb a free radicals, such as hydroxyl ( OH ) , ionized oxygen molecule ( O2- ), and nitric oxide ( NO ). Free radicals are generated by ionizing radiation and are is estimated to cause almost 70% of biological damage to DNA, proteins, and cellular membranes, the hydroxyl radical most especially. While there are antioxidants that can clean these oxidized radicals up, many of them do not do so permanently. They can release the radical and recapture it and release it and ... (called redox cycling) back into the body to cause damage again, for example vitamin C. However, melatonin, once oxidized by such a radical, terminally breaks apart, but does not release the radical. Its pieces apparently can also consume more free radical, in fact, a single melatonin molecule can consume up to ten free radical molecule species!


Background: So why be concerned with these cancers, especially breast cancer? Well, after skin cancer, breast cancer is the most common cancer among women in the US, and it is the second leading cause of cancer death in women, after lung cancer. Those issues are better covered in our Light Pollution and Breast Cancer pages. How it affects men and their prostates is still being worked out.

The problem is that even weak amounts of light impedes our pineal gland from creating the beneficial melatonin. Without melatonin, other glands produce hormones unchecked, which lead to greater cancer rates. In our industrialized societies, light pollution or light at nights becomes harder and harder to avoid, even if you knew to avoid it. Everyone's impression is that it is only light. And this apathetic acceptance may be a reason for the ever greater breast cancer rates in industrialized societies. Technology is only good when it is properly used. So while we may herald modern and super-lit technological society, when it threatens our health, it needs to be called into question, even if it is just light.

Summary: Does light pollution directly cause cancer? No. Unlike in astronomy, light itself is not the problem.

It is our biological reactions to the light that is the problem.

So, the next time that someone says to you but it's just light, tell them: no, light is our biological triggering input that suppresses a cascade of subtle, health improving functions that should naturally and nightly occur in our bodies. These functions include those that promote better sleep, fight depression, fight obesity, and consume free radicals which damage DNA and cells and negate some risk factors for certain cancers. It is NOT just light.

Because more of us are sleeping in overly lit nights, light pollution has been found to be a missing, aggravating factor that suppresses melatonin levels in humans at night. This change pulls out the stops to cancer cell growth. The hormone melatonin normally suppresses cancer cell growth and can even cause cancer cell death. In women, it does this by inhibiting the sex ovaries from growing too fast and from releasing hormones can cause breast tissue cells to multiply faster. This would increase the chance that they become cancerous. The papers mentioned below examine this effect in detail. Once you are done here, you may want to head over to our Prevent Light Pollution page to find steps you can take to end this problem to yourself and others.

The papers that have been reviewed are reorganized by subject and by date in this listing. I have commented on them in a chronological sequence below.

Lights at night, melatonin levels and prostate cancer in men:

Back to Light Pollution vs. Human Health


Prospective Cohort Study of the Risk of Prostate Cancer among Rotating-Shift Workers: Findings from the Japan Collaborative Cohort Study

Source: American Journal of Epidemiology, 2006, Vol. 164, No. 6, pages 549 - 555.

Tatsuhiko Kubo1,2, Kotaro Ozasa3, Kazuya Mikami4, Kenji Wakai5, Yoshihisa Fujino6, Yoshiyuki Watanabe7, Tsuneharu Miki4, Masahiro Nakao7, Kyohei Hayashi3, Koji Suzuki8, Mitsuru Mori9, Masakazu Washio9, Fumio Sakauchi9, Yoshinori Ito10, Takesumi Yoshimura11, and Akiko Tamakoshi10

1Dept. of Clinical Epidemiology, University of Occupational and Environmental Health, Kitakyushu, Japan.
2Dept. of Urology, University of Occupational and Environmental Health, Kitakyushu, Japan.
3Dept. of Epidemiology for Community Health and Medicine, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
4Dept. of Urology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
5Div. of Epidemiology and Prevention, Aichi Cancer Center Research Institute, Nagoya, Japan.
6Fukuoka Institute of Occupational Health, Fukuoka, Japan.
7Dept. of Urology, Meiji University of Oriental Medicine, Kyoto, Japan.
8Dept. of Public Health, Fujita Health University School of Health Sciences, Toyoake, Japan.
9Dept. of Public Health, Sapporo Medical University School of Medicine, Sapporo, Japan.
10Dept. of Preventive Medicine/Biostatistics and Medical Decision Making, Nagoya University Graduate School of Medicine, Nagoya, Japan.
11Fukuoka Institute of Health and Environmental Sciences, Dazaifu, Japan.

Shift workers have been reported to have an increased risk of some cancers. However, the risk of prostate cancer in shift workers is not known to have been examined previously. This study prospectively examined the association between shift work and risk of prostate cancer incidence among 14,052 working men in Japan enrolled in a large-scale prospective cohort. A baseline survey was conducted between 1988 and 1990. Subjects were asked to indicate the most regular work schedule they had undertaken previously: day work, rotating-shift work, or fixed-night work. During 111,974 person-years, 31 cases of prostate cancer were recorded. The Cox proportional hazards model was used to estimate the risk, with adjustments for age, family history of prostate cancer, study area surveyed, body mass index, smoking, alcohol drinking, job type, physical activity at work, workplace, perceived stress, educational level, and marriage status. Compared with day workers, rotating-shift workers were significantly at risk for prostate cancer (relative risk = 3.0, 95% confidence interval: 1.2, 7.7), whereas fixed-night work was associated with a minor increase in risk. This report is the first known to reveal a significant relation between rotating-shift work and prostate cancer.


Global Co-Distribution of Light at Night (LAN) and Cancers of Prostate, Colon, and Lung in Men.

Source: Chronobiology International: The Journal of Biological & Medical Rhythm Research, 2009, Vol. 26, Issue 1, p108-125.

Kloog, Itai1, Haim, Abraham2, Stevens, Richard G.3 and Portnov, Boris A.1

1Department of Natural Resources & Environmental Management, Faculty of Social Sciences, University of Haifa, Haifa, Israel.
2Departments of Biology & Evolutionary and Environmental Biology, University of Haifa, Haifa, Israel.
3University of Connecticut Health Center, Farmington, Connecticut, USA.

The rates of cancer are different for men the world over. The researchers examined the rates of the three most common cancers, prostate, lung, and colon, that strike men all over the world and compared those rates with the men's exposure to light at night (LAN). They took into account population density and developmental and environmental indicators, including per capita income, percent urban population, and electricity consumption. Using different mathematical models, they found a definite association between LAN exposure and prostate cancer, but not so between lung and colon cancer. This supports the theory that LAN causes melatonin levels to decrease allowing for cancer stimulating hormones to flourish. They found that those populations that had the highest LAN exposures incurred more than double the risk of prostate cancer compared to the lowest LAN exposed populations. However, the researchers also caution that the linkage is still not as clear as they would like as there still are other factors that still need to be examined.


Melatonin May Lower Prostate Cancer Risk

Title: Urinary melatonin levels, sleep disruption, and risk of prostate cancer

Source: American Association for Cancer Research, Prostate Cancer Foundation Conference, Advances in Prostate Cancer Research, January 18-21, 2014, San Diego, CA

Sarah C. Markt1, Lara G. Sigurdardóttir2, Jennifer R. Rider1, Sebastien Haneuse1, Katja Fall3, Eva S. Schernhammer4, Erin E. Flynn-Evans5, Julie L. Batista1, Lenore Launer6, Tamara Harris6, Thor Aspelund7, Meir J. Stampfer4, Vilmundur Gudnason7, Charles A. Czeisler5, Steven W. Lockley5, Unnur A. Valdimarsdóttir2, Lorelei A. Mucci1.

1Harvard School of Public Health, Boston, MA
2University of Iceland, Reykajvik, Iceland
3Örebro University Hospital, Orebro, Sweden
4Channing Division of Network Medicine, Boston, MA
5Harvard Medical School, Boston, MA
6National Institute on Aging, Bethesda, MD
7Icelandic Heart Association, Kopavogur, Iceland.

Higher levels of melatonin, a hormone involved in the sleep-wake cycle, may suggest decreased risk for developing advanced prostate cancer, according to results presented by Sarah C. Markt, M.P.H. at the AACR-Prostate Cancer Foundation Conference on Advances in Prostate Cancer Research, held on Jan. 18-21.

Melatonin is a hormone that is produced exclusively at night in the dark and is an important output of the circadian rhythm, or the body's inherent 24-hour clock. Many biological processes are regulated by the circadian rhythm, including the sleep-wake cycle. Melatonin may play a role in regulating a range of other hormones that influence certain cancers, including breast and prostate cancers.

"Sleep loss and other factors can influence the amount of melatonin secretion or block it altogether, and health problems associated with low melatonin, disrupted sleep, and/or disruption of the circadian rhythm are broad, including a potential risk factor for cancer," said Sarah C. Markt, M.P.H., doctoral candidate in the Department of Epidemiology at Harvard School of Public Health in Boston. "We found that men who had higher levels of melatonin had a 75 percent reduced risk for developing advanced prostate cancer compared with men who had lower levels of melatonin."

"Our results require replication, but support the public health implication of the importance of maintaining a stable light-dark and sleep-wake cycle," added Markt. "Because melatonin levels are potentially modifiable, further studies of melatonin and prostate cancer risk and progression are warranted."

To investigate the association between urine levels of the main breakdown product of melatonin, 6-sulfatoxymelatonin, and risk of prostate cancer, Markt and colleagues conducted a case-cohort study of 928 Icelandic men from the AGES-Reykjavik cohort between 2002 and 2009. They collected first morning void urine samples at recruitment. The morning urine samples are a considered to be a good marker of melatonin production in both men and women. They also asked the participants to answer a questionnaire about their usual sleep patterns. However, because "the sleep questionnaire did not ask men whether they used the dietary supplement melatonin as a sleep aid, there was no way to tell if the men's melatonin levels resulted from the naturally occurring form of the hormone or melatonin supplements," Markt said.

The researchers found that one in seven men reported problems falling asleep, one in five men reported problems staying asleep, and almost one in three reported taking sleeping medications.

The median value of 6-sulfatoxymelatonin in the study participants was 17.14 nanograms per milliliter of urine. Men who reported taking medications for sleep, problems falling asleep, and problems staying asleep had significantly lower 6-sulfatoxymelatonin levels compared with men without sleep problems, according to Markt.

Of the study participants, 111 men were diagnosed with prostate cancer, including 24 with advanced disease. The researchers found that men whose 6-sulfatoxymelatonin levels were higher than the median value had a 75 percent decreased risk for advanced prostate cancer. A 31 percent decreased risk for prostate cancer overall was observed as well, but this finding was not statistically significant.

"This is the first study to show a link between melatonin levels and prostate-cancer risk using urine samples collected before the men were diagnosed with the disease. Although the study was small and the results need to be replicated, these findings are important because they provide further support for the idea that men's circadian rhythms influence prostate-cancer development. Two of the best ways to preserve melatonin production are to keep a regular sleep schedule and to avoid light at night from sources like a television, computer screen, lamp or other type of indoor lighting," Markt said.

"Further prospective studies to investigate the interplay between sleep duration, sleep disturbance, and melatonin levels on risk for prostate cancer are needed," said Markt.

This study was funded by the Harvard Catalyst. Markt declared no conflicts of interest.


Department of Physics
Florida Atlantic University
Boca Raton, Florida
E-mail: vandernoot at sci dot fau dot edu
Phone: 561 297 STAR (7827)

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