The Light Pollution Factor in Human Breast and Prostate Cancers

Just as there are many different pathes that one can take to get to a particular desination, 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 them is what we often try to do. However, light pollution is one factor that is increasingly hard to escape from due to its pervasiveness in society. 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 correct.

As a quick introduction (or just for those who are impatient), here is an audio report from Heartbeat Radio about the health problems with light pollution. Another is recently covered in a series about night work on CNN.com

For those that want to know what to do to correct this problem from affecting them or their neighbors, head over to our Light Pollution Prevention page for ideas and tips.

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. In 2007, it was estimated that 178,000 new breast cancer cases would occur and that 40,000 women would die as a result. That is according to the American Cancer Society's Cancer Facts & Figures 2009 report.

The suspicion that health problems in humans are connected with lights on at night or light pollution started quite a while ago. What I'll try to cover here is predominately based on my understanding and so is a selected and rather incomplete coverage of the evolution of thought regarding this issue. It covers some key topics in what limited time I have to devote to it. But as I find it to be so important, then it is a worthy usage of that time. This page is a growing collection of papers that is still being worked on. So tune in again later on as it too evolves. Each of the papers chronologically reviewed here will have key findings highlighted, and the citations to the paper, online if possible, so that you can follow up and corroborate what is covered.

The science in a nutshell: At night, the hormone melatonin should naturally be secreted by the pineal gland, which lies just under our brains. The pineal gland has a link to the retinal cells in our eyes through the brain's suprachiasmatic nuclei (SCN), which is a collection of brain cells that is the center of our biological clocks or our circadian system. These photosensitive eye cells are active or sensitive to a particular blue wavelength which does not activate the retinal rods or cones cells that you may have learned about in biology class, hence they seem to be an entirely new photosensitve cell in the eyes. These cells inform the brain's SCN that it is night and the SCN tells the pineal gland to make melatonin, but it does it only when it is dark. Thus, melatonin is the chemical signal our body's use to understand that it is nighttime and to then start certain health inducing activities.

Once in the blood, melatonin also reaches other hormone producing glands, such as the ovaries and the pitutary gland, and stops the production of their hormones. The hormones that come from these glands: estrogen, progestrone, focille stimulating hormone (F.S.H.), and the lutenizing hormone (L.H.), can cause rapid breast tissue cell growth. Cellular growth and turnover can create errors in their genetic coding, which can leads to cancer. Ever greater growth means ever greater and more frequent chances for error, and so, ever greater chances of cancer. Note that a common approach to fighting cancer is to use hormone suppressant therapies Instead of society expecting that a pill will be one day invented that will cure breast cancer, it seems to me that we should avoid causing it in the first place by using our own natural suppressant abilities. This should be everyone's first step even before cancer occurs.

The problem is that even weak amounts of light impedes our pineal gland from creating the beneficial melatonin. Without melatonin, those glands produce hormones unchecked and out of control and that leads to ever greater breast 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. For everyone's impression has been that it is only light. However, this seems to be the 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: So does light pollution directly cause cancer? No. Unlike in astronomy, light itself is not the problem.

Because more of us are sleeping in overly lit nights, that 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. 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.

• Factors and conditions that reduce human melatonin levels, which then stimulates breast cancer
• Excerpt of the Melatonin Summary from the National Cancer Institute
• Geographic Patterns of Breast Cancer in the U.S.
• Role of pineal gland in aetiology and treatment of breast cancer.
• Two letters responded to pineal gland aetiology and breast cancer.
• Cohen, Lippman and Chabner reply to the two letters about their Pineal Gland and Breast Cancer review
• Effect of Melatonin on Mammary Carcinogenesis in Intact and Pinealectomized Rats in Varying Photoperiods
• Light pollution, lights at night, melatonin levels and breast cancer in women
• Electric Power Use and Breast Cancer: A Hypothesis
• Inverse association between breast cancer incidence and degree of visual impairment in Finland
• Night Shift Work, Light at Night, and Risk of Breast Cancer
• Rotating Night Shifts and Risk of Breast Cancer in Women Participating in the Nurses' Health Study
• Blocking Low-Wavelength Light Prevents Nocturnal Melatonin Suppression with No Adverse Effect on Performance during Simulated Shift Work
• Melatonin-Depleted Blood from Premenopausal Women Exposed to Light at Night Stimulates Growth of Human Breast Cancer Xenografts in Nude Rats
• Light at Night Co-distributes with Incident Breast but not Lung Cancer in the Female Population of Israel.
• Light-at-night, circadian disruption and breast cancer: assessment of existing evidence
• Lights at night, melatonin levels and prostate cancer in men
• Prospective Cohort Study of the Risk of Prostate Cancer among Rotating-Shift Workers: Findings from the Japan Collaborative Cohort Study
• Global Co-Distribution of Light at Night (LAN) and Cancers of Prostate, Colon, and Lung in Men.
• Responses to health hazards by lights at night
• IARC Monographs Evaluates the Carcinogenic Risks of Shiftwork to Humans
• American Medical Association UNANIMOUSLY passes Resolution 516 against Light Pollution -- New Page
• A New Possible Link Between Light Pollution and Obesity!
• Other sites about the negative health effects of light pollution

Excerpt of the Melatonin Summary from the National Cancer Institute

The risk effect surrounds the signaling hormone melatonin whose production is dark dependent. Its usage in the body is numerous. From the U.S. government's website on cancer about melatonin is this quote:

Melatonin is involved in circadian rhythm regulation, sleep, hormonal expression of darkness, seasonal reproduction, retinal physiology, antioxidant free-radical scavenging, cardiovascular regulation, immune activity, cancer control, and lipid and glucose metabolism. It is also a new member of an expanding group of regulatory factors that control cell proliferation and loss and is the only known chronobiotic hormonal regulator of neoplastic cell growth.

At physiological concentrations, melatonin suppresses cell growth and multiplication and inhibits cancer cell proliferation in vitro through specific cell-cycle effects. At pharmacological concentrations, melatonin suppresses cancer cell growth and multiplication. At physiological and pharmacological concentrations, melatonin acts as a differentiating agent in some cancer cells and lowers their invasive and metastatic status by altering adhesion molecules and maintaining gapjunction intercellular communication. In other cancer cell types, melatonin, alone or with other agents, induces programmed cell death.

David Blask, M.D., Ph.D.
Laboratory of Experimental Neuroendocrinology/Oncology
Bassett Research Institute
Cooperstown, NY.

South Florida residents please take note! You can probably contact the FAU library via your local libraries to get access to the included journal papers. The FAU Library is participating in the Sunshine Library Card program. So you may be able to follow up on these or any other journal we have here.

Geographic Patterns of Breast Cancer in the U.S.

Journal of the National Cancer Institute, 1977, Vol. 59, p1407-1411.

William J. Blot, Joseph R. Fraumeni Jr, B. J. Stone

Environmental Epidemiology Branch, National Cancer Inst.,
National Institute of Health, Public Health Service
U.S. Dept. of Health, Education and Welfare, Bethesda, MD

The researchers calculated correlations between the mortality rates for premenopausal and postmenopausal women and demographic data for the 3,056 U.S. counties from 1950 to 1969. They found a northern predominance of the tumors in postmenopausal women and a particular high rate of breast cancer mortality in the northeast and other urban centers, but a uniform tumor distribution in premenopausal women across the country. Income status, German ethnicity and colon cancers where strong indicators for postmenopausal women, but it only partially explained the geographic distribution, this suggests an extrinsic risk factor that they did not find. Fertility patterns and ovarian cancers were more likely to be linked to premenopausal women's breast cancer, which suggests the importance of reproductive and genetic determinants.

The data told them that the mortality rates:

• increased with urbanization across the country, only in the South were rates in large population centers not high.
• increased with the median family income, and to a lesser extent, education levels.
• decreased with high birth rates, especially for younger mothers (rates for 1st time mothers younger than 18 were 1/3rd the rate for 1st time mothers older than 35).
• grew stronger for migrant groups, such as Japanese-Americans, as they westernized.

Blot, Fraumeni and Stone suggested that environmental factors lead to the changes of breast cancer risk. But what those factors are they could only suggest temperature (because of a latitudinal gradient) or diet (because of the increased risk due to the westernizing of migrant groups). Their paper discusses the effect of urbanization, but a direct correlation between increased light pollution and breast cancer risk is not mentioned, nor does not occur to the authors.

To help you see this affect of the light pollution concept, I have collected and tried to match the data maps from two different studies. I chose to focus on the northeastern quarter of the U.S. for it is my understanding is that the population demographics there for the study's time period did not change much, thus any demographic differences should not affect the comparison. What is difficult in the comparisons, however, is that the data maps use two different projections for their presentations.

The colorful first map below is from the light pollution study done by P. Cinzano, F. Falchi, C. D. Elvidge. ISTIL, Thiene, Italy. © 2001. Cinzano's map was presented in a cylinderical, Mercator projection as what would be viewed from a equatorial orbiting satellite. His mid-1970s data map of the same region's light pollution is the closest to the time that I can find that correlates with Blot, Fraumeni and Stone's study. Hence the more northern states in Cinzano's map appeared a bit squished. However, William Plate, Assist. Dir of FAU's Office of Comm., was very kind to stretch and warp Cinzano's map so that it would better match the authors' map. The LP and Astronomy page shows more on the growth of light pollution in U.S. and what it is projected to become in 2025.

The second map below is the authors' greyscale mapping by county of the incidences of postmenopausal breast cancer from 1950 to 1969. It is presented in the cartographer's point of view as would be seen from above the U.S. In the authors' map, the darker the county, the higher the incidence of breast cancers occured.

For the final map, I just transparently overlaid the warped Cinzano's map onto Blot's map for an immediate comparison. You should be able to see that all the colorful, bright areas of Cinzano's map pretty well matches up with the dark/high breast cancer areas of Blot's map. With a bit of thought, you should be able to recognize the East Coast corridor, find Cape Cod, the Chesapeake, the density of the cities west of Lake Michigan, the cities of Cleveland and Buffalo. You'll also note that there are cities of southern Canada that are in Cinzano's map which Blot did not cover.

This exercise shows that the higher density of breast cancer cases correlates with those areas of high urbanization and thus high levels of light pollution. To see the different maps, just move your mouse over the maps to see how each compares to the other.

Additional credit: P. Cinzano, F. Falchi, C. D. Elvidge. Copyright 2001 ISTIL, Thiene. Reproduced from ISTIL Report 2001.

Role of pineal gland in aetiology and treatment of breast cancer.

Lancet, Oct 14^th 1978, Vol. 2, p814–16.

Michael Cohen, Marc Lippman and Bruce Chabner

Clinical Pharmacology and Medicine Branches, National Cancer Institute
National Institutes of Health, Bethesda, Maryland, U.S.A.

This paper cited 44 papers and summed up their results into the hypothesis in that:

• Diminished functions of the pineal gland depress its melatonin production.
• Depressed melatonin production allows for ovarian growth and greater hormonal production.
• Greater hormonal production leds to eariler sexual maturation, early puberty and greater breast cancer development.

The authors looked at the evidence of pineal calcification (p.c.). This means that the pineal gland near the brain becomes heavier due to an increased concentration of calcium in it. p.c. naturally occurs as all populations age, but at very dissimilar rates. Their paper focused on answering why this is so and some aspects of p.c. Were the rate differences due to differences in breast cancer disease in the population, or, as they argued, did it cause the breast cancer differences? p.c. was measured using skull x-rays. They also cited evidence that transplanted tumors to pinealectomized animals grew larger and became more malignant compared to control groups and giving them melatonin could abolish the damage. Pinealectomy is, in effect, the removal of the pineal gland. While this could be achieved via surgery, it eventually occurs during increased p.c. It is also easy to achieve by subjecting the animal to continuous, 24 hour light. The light, just like the increased calcification, shuts off the pineal gland's production of melatonin, as it naturally only operates in the dark. Melatonin inhibits the ovarian glands from increasing in size and so limits their production of hormones, such as oestrogen, progesterone, FSH and LH. These hormones increase the rate of cellular growth in the breast, leading to greater chances of genetic error and thus breast cancer.

The hypothesis that diminished function of the pineal gland may promote the development of breast cancer in human beings is suggested by the relation between breast cancer and prolonged oestrogen excess, and by the observation that the pineal secretion, melatonin, inhibits ovarian oestrogen production, pituitary gonadotrophin production, and sexual development and maturation.

Their points on this are:

• pineal calcification (p.c.) is highest in countries with high rates of breast cancer, and lowest in areas of low incidence
• incidences of p.c. & of breast cancer are moderate among black populations in the U.S.
• psychiatric patients taking chlorpromazine, which raises serum-melatonin levels, have lower incidences of breast cancer
• pineal and melatonin may influence tumor induction and growth in experimental animals (found to be true later that year)
• the melatonin receptor in human ovaries suggests a direct influence of this hormone on ovarian function and oestrogen production
• impaired pineal secretion is believed to be an important factor in triggering puberty, which is a risk factor in breast cancer.

They mention that factors that can impair pineal secretion are:

• differences in visual stimulation, either by blindness or by darkness at night,
• increased pineal calcification,
• changes in feedback hormones by peripheral endocrine secretions.

They sum up by writing that Our hypothesis also suggests that melatonin, by suppression of oestrogen secretion, or by direct inhibitory effects on breast tissue, might suppress induction of breast cancer.

Two letters responded to the Cohen, Lippman & Chabner paper in the Lancet Nov. 4th journal of that year.

Lancet, Nov 4^th 1978, v2, p1001–2.

The first letter was by E. Tapp.

Group Laboratory, Preston Royal Infirmary, Preston, Lancashire

Tapp, citing five papers, argued about the use of radiology in the detection of p.c., saying that the detected calcification was due to individual areas of calcification in the pineal gland and not of the entire gland. He wrote that calcification was constant throughout life and did not increase with age. So he discounted the radiological evidence linking breast cancer patients with increased p.c., thus came to the conclusion that the reverse was true.

He stated that dying cancer patient's pineal glands were heavier than those dying of other diseases.

He then talks about states that melatonin increases prolactin secretion and that is implicated in the development of breast cancer. He said that inducing breast tumors in rats had an increased malignancy if melatonin is given, just as there is an increased malignancy if prolactin is given. He then said that Hamilton found that continuous daylight, which should suppress the pineal gland, resulted in shrinkage in the incidence and malignancy of the tumors. He promised to present further melatonin level data in breast cancer patient showing this later on.

Note, I am currently not able to produce the Hamilton paper (Hamilton, T., Br. J. Surg., 1969, v56, p764), but will review it when I can later on.

Lancet, Nov 4^th 1978, Vol. 2, p1002.

The next letter was by Rashida Karmali¹ and by D. F. Horrobin² and T. Ghayur².

¹Dept of Pathology and Lab. Medicine, East Caroline Univ. School of Med., Greenville, NC, USA
²Clinical Research Inst., Montreal, Quebec, Canada

Their preliminary results confirmed what Cohen, Lippman and Chabner said. They found that melatonin inhibits tumor growth in rats with an intact pineal gland. The data result is based on 1 mg of melatonin / day on the growth of a mammary tumor that was transplanted into a rat.

They also pointed out that the protective action of chlorpromazine may be two fold, 1.) in that it raises melatonin levels, which inhibits oestrogen levels, and 2.) it raises prolactin levels as well, which inhibits growth in some animal tumors. So in the case of chlorpromazine, the effect of melatonin could just be suppressing oestrogen levels and no more. They do finish their letter pointing out that melatonin stimulates a thromboxane A₂-like substance in rats, and that their preliminary work suggests that an error in the thromboxane A₂ synthesis leads to tumor growth, but those agents (i.e. melatonin) that stimulate the thromboxane creation significantly inhibits tumor growth.

Cohen, Lippman and Chabner respond back to the two letters about their Pineal Gland and Breast Cancer review

Lancet, Dec 23^rd & 30^th, 1978, Vol. 2, p1381-2.

Cohen, Lippman and Chabner respond by first saying that radiology is an insensitive way to study pineal calcification, there is a definite correlation between the degree of calcification and the detectability of pineal calcification on skull X-rays. They mention the earlier work of Tapp and Huxley that shows the pineal calcification increases with the age of the female between ages 14 to 59, which matches what the X-rays show.

Pineal glands of dying cancer patients are heavier than those dying of other diseases for the increased calcification could account for the higher weight. They do state that this increase in pineal activity and pineal hypertrophy could be caused by the metastatic cancer, leading to increased pineal weight. Then the secondary hypersecretion of melatonin would be a possible reaction to the metastatic cancer."

They state that Tapp incorrectly mentioned Hamilton's work. It was that he showed that animals intubated with dimethylbenzanthracene (DMBA) and kept in continuous light (this would decrease melatonin secretion) as opposed to controls in diurnal lighting had a higher incidence of tumors, but that those tumors were less malignant in their histopathological appearance.

They state that Most published works supports the view that melatonin inhibits tumor induction, growth, and metastatsis, as we said in our paper Oct 14. They express interest in the "letter of Dr. Karmali and colleagues (Nov. 4. p 1001) which supports this contention and gives, for the first time, published evidence of such effect on breast cancer."

Please note that you should be able to use the links to the original papers for those now discussed below.

Effect of Melatonin on Mammary Carcinogenesis in Intact and Pinealectomized Rats in Varying Photoperiods

Cancer Research, August 1984, Vol. 44, No. 8, p3403-3407.

Prabhaker N. Shah, Molina C. Mhatre, and Lalita S. Kothari
Endocrinology Division, Cancer Research Institute, Parel, Bombay 400012, India

Exposure of female Holtzman rats to constant light (24 hr/day) immediately after birth significantly increased 9,10-dimethyl-1,2-benzanthracene-induced mammary cancer.

Administration of melatonin (500 μg/day/rat i.p. given from 52 to 145 days of age) completely abolished the effect of the functional pinealectomy by sharply reducing 9,10-dimethyl-1,2-benzanthracene-induced cancer incidence from 95% to 25% during the post-9,10-dimethyl-1,2-benzanthracene observation period which lasted up to 180 days.

On the other hand, administration of melatonin to surgically pinealectomized animals (labeled PX rats) exposed to constant light reversed the effect only partially by reducing the cancer incidence from 83% to 53%.

Further, melatonin treatment in intact and surgically pinealectomized animals exposed to a short photoperiod revealed qualitatively similar differences in suppression of the cancer incidence. From these results, it is concluded that, to have an impressive antitumor effect, presence of the pineal gland is essential, and the probable site of melatonin action appears to be at both the pineal gland and the hypothalamus.

To study the effect of melatonin on mammary tumorigenesis, a classical endocrinological maneuver is used in this study by exposing female rats to constant light immediately after birth. In such "functionally pinealectomized" young virgin rats, melatonin deprivation removes its inhibitory regulatory control over the hypothalamic-hypophysial axis leading to constant availability of estrogen and elevated circulating PRL. In response to these changes in the hormonal profile, there occur premature sexual maturation, prolonged estrus, and prolonged mammary gland stimulation.

This is what the authors conclude in their abstract. Obviously, since a continuous exposure to light, in effect, pinealectomizes the animal, which in turn, fails to protect the animal from breast cancer, then continuous exposure to light is to be avoided if one wants to avoid the cancer. To learn more the effects light pollution has on plants and animals of many different kinds, please visit our Light Pollution vs. Nature pages.

Dr. Richard G. Stevens, made a connection about the earlier papers and suspected that the general increased light pollution throughout society was the reason for the growth of breast cancer rates, especially in industrialized areas. The next paper covered is his proposed hypothesis.

Electric Power Use and Breast Cancer: A Hypothesis

American Journal of Epidemiology, 1987, Vol. 125, No. 4, p556-561.

Richard G. Stevens

(at the time of the paper:) Pacific Northwest Laboratory, Richland, WA
(currently:) Professor of Community Medicine and a Cancer Epidemiologist of the Department of Community Medicine and Healthcare, University of Connecticut Health Center, Farmington, CT

In this paper Dr. Stevens reviewed what is known about the epidemiology of breast cancer and based on that proposed a hypothesis. He reviewed the facts that

• large differences exist among populations in breast cancer incidences and mortality
• incidence rates are: low in Africa & Asia, intermediate in southern Europe and South America, and high in northern Europe and North America
• race does not account for the different rates, Japanese migrant studies show low rates in Japan, medium rates in Japanese in Hawaii, and high rates in Japanese in California
• Japanese women have 1/5th the rate of US women, though they are rising as Japan "westernizes"
• diet does not prove to be a conclusive cause of breast cancer, while rates correlate with per capita fat consumption, that appears to be a cultural coincidence, as studies show on an individual basis the risk correlation is inconclusive
• reductions in the pineal gland's melatonin production increases breast cancer risk and that "environmental lighting" can achieve that same effect
• that electricity provides the lighting and is used in ever greater amounts in metropolitan centers and populations in those urban settings show an in increase in breast cancer risk

So, a light went off in Dr. Stevens' head. He proposed that it is the use of electric power, either from the lights that the electric grid powers or from the varying e-fields from the grid itself which is causing increase the risk of breast cancer in urban cities. The hypothesis is based on experimental evidence that shows an effect of light and extremely low frequency electric and/or magnetic (ELF) fields on pineal melatonin production, and on the relationship of melatonin to mammary carcinogenesis.

He then covers some papers that look into partial aspects of this concept. For the electric fields he notes an experiment on rats that used very large fields of strengths varying from 1.5 to 65 kV/m for 20 hours a day for 30 days. Due to body shapes, the 1.5 kV/m field should be equivalent to a 100-500 V/m field strength in humans. While there were differences of melatonin levels between exposed rats and their controls, the field strength is well above levels populations are routinely exposed to. He also pointed out another study, though small in scale, which failed to find a connection between cancer mortality in those near electrical transmission lines in Britain.

However, he noted a study that showed that very low light levels, 22 nW/cm² (that is 22 Billionths of a watt per square cm!), were enough to reduce pineal melatonin production in rats. Humans have a similar response, though at higher levels.

On this basis, chronic lack of a dark night in high electric-use communities may simulate low level "constant-light", and contribute to the geographic variation in breast cancer.

He suggested that an experiment of three groups of rats be done. The first group of an electric field, the second of constant light and the last being the control where neither was done and compare the results.

Also consider this information in regards to migrant groups. The first generation that arrives to a light polluted county in the U.S. may not have had an initial light pollution exposure. As they stay in the U.S., their exposure to the light continues to affect their hormones. Subsequent generations then born in the U.S. develop in the womb of their mothers that have growing hormonal alterations. Every generation undergoes this same hormonal alteration on top of the general growing light pollution.

It was stated earlier that the pineal gland makes the melatonin, but only does so when it is dark. How dark does it have to be? Well, as a simple rule:

That's right, no nightlights, television, nor hall lights should be left on. Windows need to curtianed against outdoor intrusive outdoor light pollution sources. Clocks with their self-luminious faces, should at least glow red or use red L.E.D.s, see below. If you think that is extreme, then consider this next study of blind women in Finland.

Inverse association between breast cancer incidence and degree of visual impairment in Finland

British Journal of Cancer, 1990, Vol. 80, No. 9, p1459-1460.

PK Verkasalo^1,2, E Pukkala³, RG Stevens⁴, M Ojamo⁵ and S-L Rudanko⁵

¹Department of Public Health, PO Box 41, FIN-00014 University of Helsinki, Finland
²National Public Health Institute, Division of Environmental Health, P.O. Box 95, FIN-70701 Kuopio, Finland
³Finnish Cancer Registry, Liisankatu 21B, FIN-00170 Helsinki, Finland
⁴Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA
⁵Finnish Register of Visual Impairment, Mäkelänkatu 50, FIN-00510 Helsinki, Finland

The researchers identified 10,935 women with visual impairment from the Finnish Registry and followed the women in the Finnish Cancer Registry between the years of 1983-1996. The researchers sorted the women based on degrees of visual impairment, counted up the number of years they were in the Registries, counted the number of breast cancer and other types of cancer cases in each group and compared that number with their expected cancer incident rates. They found a decrease in breast cancer rates as the visual impairment increased in the women. No similar correlation was found with the other types of cancers and in fact their rates were slightly increased. Here is the breakdown of their numbers:

The Expected Breast Cancer numbers comes from the cancer incidence rates of each group times their number of person-years. The SIR or the Standardized Incidence Ratios is just the Observed Breast Cancer numbers divided by the Expected Breast Cancer numbers for each group. As the less blind groups had greater numbers, their cancer incident rates approached the national average rates. However as the populations in the groups with greater visual impairment were smaller in number, their cancer incident rates would be more affected by the health of individuals in the groups. While the 50% reduction in breast cancer rates in totally blind women was based on a small numbers, it did match risk estimates from two other studies.

Thus this study found that those women with normal vision had twice the risk of breast cancer compared to those which were totally blind. Note that the study did not break down the sighted women by their lights-at-night exposures. Had they done so, we could have had even better understanding of the risk factors.

The next two studies did exactly that by identifying those women who worked non-regular shifts, their sleeping conditions and whether they had breast cancer. The first study was a randomized investigation of women that were contacted via the telephone. The second study looked at women participating in a Nurse's health study. As if their jobs were not streesful or hard enough, now it seems that their very work places, due to the times at which they work, is cancerous.

Night Shift Work, Light at Night, and Risk of Breast Cancer

Journal of the National Cancer Institute, Oct. 17, 2001, Vol. 93, No. 20, p1557-1562.

Scott Davis^1,2, Dana K. Mirick³, Richard G. Stevens⁴

¹Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA
²Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle
³Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center
⁴Department of Community Medicine, University of Connecticut Health Center, Farmington.

Exposure to light at night may increase the risk of breast cancer by suppressing the normal nocturnal production of melatonin by the pineal gland, which, in turn, could increase the release of estrogen by the ovaries. This study investigated whether such exposure is associated with an increased risk of breast cancer in women. Methods: Case patients (n = 813), aged 20-74 years, were diagnosed from November 1992 through March 1995; control subjects (n = 793) were identified by random-digit dialing and were frequency matched according to 5-year age groups. An in-person interview was used to gather information on sleep habits and bedroom lighting environment in the 10 years before diagnosis and lifetime occupational history. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by use of conditional logistic regression, with adjustment for other potential risk factors.

Results: Breast cancer risk was increased among subjects who frequently did not sleep during the period of the night when melatonin levels are typically at their highest (OR = 1.14 for each night per week; 95% CI = 1.01 to 1.28). Risk did not increase with interrupted sleep accompanied by turning on a light. There was an indication of increased risk among subjects with the brightest bedrooms. Graveyard shift-work was associated with increased breast cancer risk (OR = 1.6; 95% CI = 1.0 to 2.5), with a trend of increased risk with increasing years and with more hours per week of graveyard shift work (P = .02, Wald chi-squared test).

The results of this study provide evidence that indicators of exposure to light at night may be associated with the risk of developing breast cancer.

Rotating Night Shifts and Risk of Breast Cancer in Women Participating in the Nurses' Health Study

Journal of the National Cancer Institute, October 17^th, 2001, Vol. 93, No. 20, p1563-1568.

Eva S. Schernhammer¹, Francine Laden^1,2, Frank E. Speizer^1,2, Walter C. Willett^1,3, David J. Hunter^1,4,5, Ichiro Kawachi^1,6, Graham A. Colditz^1,3,7

¹Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA
²Department for Environmental Health, Harvard School of Public Health, Boston
³Departments of Epidemiology and Nutrition, Harvard School of Public Health
⁴Department of Epidemiology, Harvard School of Public Health
⁵Harvard Center for Cancer Prevention, Boston
⁶Department of Health and Social Behavior, Harvard School of Public Health
⁷Epidemiology Program, Dana-Faber/Harvard Cancer Center, Boston.

Melatonin shows potential oncostatic action, and light exposure during night suppresses melatonin production. There is little information, however, about the direct effect of night work on the risk of cancer. The researchers investigated the effect of night work in breast cancer.

The researchers examined the relationship between breast cancer and working on rotating night shifts during 10 years of follow-up in 78,562 women from the Nurses’ Health Study. Information was ascertained in 1988 about the total number of years during which the nurses had worked rotating night shifts with at least three nights per month. From June 1988 through May 1998, they documented 2441 incident breast cancer cases. Logistic regression models were used to calculate relative risks (RRs) and 95% confidence intervals (CIs),adjusted for confounding variables and breast cancer risk factors. All statistical tests were two-sided.

The authors observed a moderate increase in breast cancer risk among the women who worked 1–14 years or 15–29 years on rotating night shifts (multivariate adjusted RR = 1.08 [95% CI = 0.99 to 1.18] and RR = 1.08 [95% CI = 0.90 to 1.30], respectively). The risk was further increased among women who worked 30 or more years on the night shift (RR = 1.36; 95% CI = 1.04 to 1.78). The test for trend was statistically significant (P = .02).

They concluded that women who work on rotating night shifts with at least three nights per month, in addition to days and evenings in that month, appear to have a moderately increased risk of breast cancer after extended periods of working rotating night shifts.

Night-shift workers face fundamental challenges, Blask says. Melatonin works, to a large degree, by inhibiting the cancer cells from taking up linoleic acid, he says. Cravings for fatty foods frequently assail workers in the middle of the night. As a result, many shift workers consume large amounts of linoleic acid just when their melatonin production is suppressed and unable to protect them from the polyunsaturated fat, he says. Newer reports are showing that this greater linoleic acid uptake, too, is becoming an additional health hazard and maybe an additional factor in the rise of obesity in industrialized communities. See more below in the Other Health Sites section.

The next study to particularly interesting from an astronomer's point of view. Red light, or those of longer wavelengths, are routinely used to function in the dark, check sky charts, record notes, and such when going out to observe at night. Red light is used because shorter wavelengths, like the blue end of the spectrum, break down rhodopsin in the eyes. Rhodopsin is what our bodies make from the vitamin A rich foods we eat, like carrots. We need it and use it so our eyes can adjust to the dark, low level light conditions. This is called our "night vision". It is what we use to see very faint objects in the sky like galaxies or comets.

What a blue sky means to us -- Go out during the day time and look up at the blue sky. Intuitively, we know that a blue sky means that it is daytime, as it has been so for millions of years now. Our brains know it. Our bodies know it. Our hormones know it. The suprachiasmatic nuclei (SCN), the center of our circadian system, knows it and responds to it. The SCN controls the pineal gland, which outputs the hormone melatonin to control the rest of our bodies. In fact, it is very the presence of the blue light that tells the SCN that it is daytime. And so, in the presence of blue light, the SCN, assuming it is daytime, acts accordingly.

Even, if it isn't.

In the presence of blue light, the SCN acts as if it is daytime, even if it is the middle of the night. We have just recently learned that there are some photoreceptive cells in our eyes that are not rods or cones, but do detect blue light and transmit that information to our suprachiasmatic nuclei. When we see this blue light, our pineal gland outputs as if it is daytime, and so then it does not create the necessary melatonin for our bodies, when we may need it.

The next study looks more carefully at simple ways to prevent blue light, or "low wavelength light", from interfering with our bodies' ability to make melatonin. After reading about it, then consider the number of people that go to bed with a light or a nightlight or a TV on. Blue light is damaging. Read the study (not just the summary offered here) and you'll find how quickly our bodies try to restore the level of melatonin in our system, once dark conditions resume, hence it seems that melatonin is quite important to our bodies. It also seems that rats can not do that. For once their melatonin levels drop due to a bright light source, the level stays down for the rest of the night. They are also more sensitive to smaller changes of light than humans. So for all the damaging affects lights at night causes us, they probably suffer a larger impact. Now I am not about to create a pity page for rats mind you, however, it does call into question the concept of how much light pollution affects other animal species. I will try to go into greater detail about that in the light pollution verses nature pages.

Personally, I would not have used the term "low-wavelength light" to describe the shorter wavelengths of blue light and the title's double negative needs decoding to something more like Blocking Shorter Wavelength Light Allows for Melatonin Secretion Without Adverse Effects on Performance during Simulated Shift Work, but well, there it is.

Blocking Low-Wavelength Light Prevents Nocturnal Melatonin Suppression with No Adverse Effect on Performance during Simulated Shift Work

The Journal of Clinical Endocrinology & Metabolism, 2005, Vol. 90, No. 5, p2755–2761.

Leonid Kayumov^1,2, Robert F. Casper³, Raed J. Hawa^1,2, Boris Perelman¹, Sharon A. Chung¹, Steven Sokalsky¹, and Colin M. Shapiro^1,2,4

¹Sleep Research Laboratory, University Health Network, Toronto, Ontario, Canada M5T 2S8
²Departments of Psychiatry, University of Toronto, Toronto, Ontario, Canada M5T 2Z9
³Departments of Obstetrics and Gynecology, University of Toronto, Toronto
⁴Departments of Ophthalmology, University of Toronto, Toronto

Decreases in melatonin production in human and animals are known to be caused by environmental lighting, especially short-wavelength lighting (between 470 and 525 nm). The researchers investigated the use of goggles, which excludes wavelengths shorter than 530 nm, could prevent the suppression of melatonin in bright-light conditions during a simulated shift-work experiment. Salivary melatonin levels were measured under dim (<5 lux), bright (800 lux), and filtered (800 lux) light at hourly intervals between 2000 and 0800 h in 11 healthy young males and eight females (mean age, 24.7 ± 4.6 yr). The measurements were performed during three nonconsecutive nights over a two week period. Subjective sleepiness was measured by self-report scales, whereas objective performance was assessed with the Continuous Performance Test. All subjects demonstrated preserved melatonin levels in filtered light similar to their dim-light secretion profile. Unfiltered bright light drastically suppressed melatonin production. Normalization of endogenous melatonin production while wearing goggles did not impair measures of performance, subjective sleepiness, or alertness.

This next paper is a real clincher. The researchers used blood from women who were either recently exposed to light or from those who stayed in darkened conditions, and found that the different blood samples caused significantly different growth rates in breast cancer tumors. Note the rate difference is between blood taken from a women after being exposed light compared that blood from a women kept in dark conditions. Then note how similar that rate difference is with Kloog, et al, 2008, study from the Univ. of Haifa in Isreal mentioned later on.

Melatonin-Depleted Blood from Premenopausal Women Exposed to Light at Night Stimulates Growth of Human Breast Cancer Xenografts in Nude Rats

Cancer Research, Dec. 1^st 2005, Vol. 65, No. 23, p11174-11184.

David E. Blask¹, George C. Brainard², Robert T. Dauchy¹, John P. Hanifin², Leslie K. Davidson¹, Jean A. Krause¹, Leonard A. Sauer¹, Moises A. Rivera-Bermudez³, Margarita L. Dubocovich³, Samar A. Jasser², Darin T. Lynch¹, Mark D. Rollag⁴ and Frederick Zalatan¹

¹Laboratory of Chrono-Neuroendocrine Oncology, Bassett Research Institute, The Mary Imogene Bassett Hospital, Cooperstown, New York
²Department of Neurology, Thomas Jefferson University, Philadelphia, Pennsylvania
³Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Feinberg School of Medicine, Chicago, Illinois
⁴Department of Anatomy, Physiology, and Genetics, Uniformed Services University of the Health Sciences, Bethesda, Maryland

The scientists in report, including the same David Blask quoted above, put MCF7 cells into mice to generate human breast cancer tumors. These tumors were then grafted into rats. (Their technique created a growing human-derived tumor with a single artery into and a single vein from the tumor. This made the tumor very controllable for the experiment.) The scientists then gave the rats blood taken from women during the day, in the earliest hours of the morning (as in 1 am to 3 am), and after being exposed to about five minutes of light at night. This last test simulated the amount of time it may take someone to turn on the light when using a bathroom. The blood that was taken during darkness and then injected into the grafts slowed the growth of the cancers by 80 percent. However, the blood taken after exposure to light, whether the light was from daytime or just from lights at night, did not slow it down at all.

WebMD.com published a news archive article about the study at Hormone Melatonin Slows Breast Cancer - Bright Light at Night Linked to Increased Cancer Risk by Daniel J. DeNoon, in July 14, 2003. The article quotes Dr. Blask as saying that Nighttime melatonin is a relevant anticancer signal to human breast cancers. Ninety percent of human breast cancers have specific receptors for this signal.

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

American Journal of Epidemiology, 2006, Vol. 164, No. 6, p549–555.

Tatsuhiko Kubo^1,2, 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.

The next study achieves what I crudely tried to show with Blot's 1977 Geographical Patterns of Breast Cancer study and Cinzano's 2001 Light Pollution Atlas. It shows a correlation between the high incidence of breast cancers in the overly lit cities of Haifa and Tel-Aviv. In fact the light pollution levels were the strongest factors in the correlations found. As was expected, no similiar corresponding relation was found for lung cancer rates.

Again compare the breast cancer rates of the light polluted areas with those in darker areas here in the Isreal study. Then note how similar this comparison is to the change in the cancer growth rates found in the Blask, et al 2005 study.

Light at Night Co-distributes with Incident Breast but not Lung Cancer in the Female Population of Israel.

Chronobiology International: The Journal of Biological & Medical Rhythm Research; 2008, Vol. 25 Issue 1, p 65-81.

Kloog, Itai¹, Haim, Abraham², Stevens, Richard G.³, Barchana, Micha^4,5, Portnov, Boris A.¹

¹Department of Natural Resources & Environmental Management, University of Haifa, Haifa, Israel.
²Department of Biology, University of Haifa-Oranim, Kiryat Tivon, Israel.
³University of Connecticut Health Center, Farmington, Connecticut, USA.
⁴School of Public Health, University of Haifa, Haifa.
⁵Israel National Cancer Registry, Ministry of Health, Jerusalem, Israel.

Recent studies of shift-working women have reported that excessive exposure to light at night (LAN) may be a risk factor for breast cancer. However, no studies have yet attempted to examine the co-distribution of LAN and breast cancer incidence on a population level with the goal to assess the coherence of these earlier findings with population trends. Coherence is one of Hill's criteria (actually, viewpoints) for an inference of causality. Nighttime satellite images were used to estimate LAN levels in 147 communities in Israel. Multiple regression analysis was performed to investigate the association between LAN and breast cancer incidence rates and, as a test of the specificity of our method, lung cancer incidence rates in women across localities under the prediction of a connection with breast cancer but not lung cancer. After adjusting for several variables available on a population level, such as ethnic makeup, birth rate, population density, and local income level, a strong positive association between LAN intensity and breast cancer rate was revealed (p<0.05), and this association strengthened (p<0.01) when only statistically significant factors were filtered out by stepwise regression analysis. Concurrently, no association was found between LAN intensity and lung cancer rate. These results provide coherence of the previously reported case-control and cohort studies with the co-distribution of LAN and breast cancer on a population basis. The analysis yielded an estimated 73% higher breast cancer incidence in the highest LAN exposed communities compared to the lowest LAN exposed communities.

IARC Monographs Evaluates the Carcinogenic Risks of Shiftwork to Humans

http://monographs.iarc.fr/ENG/Classification/ClassificationsAlphaOrder.pdf (Vol. 98; in preparation, pg 22)

http://monographs.iarc.fr/ENG/Classification/ClassificationsGroupOrder.pdf (Vol. 98; in preparation, pg 7)

The International Agency for Research on Cancer (IARC) is part of the UN's World Health Organization. The IARC Monographs identify environmental factors that can increase the risk of human cancer. These include chemicals, complex mixtures, occupational exposures, physical and biological agents, and lifestyle factors. National health agencies use this information as scientific support for their actions to prevent exposure to potential carcinogens. The IRAC Monographs on the Evaluation of Carcinogenic Risks to Humans Vol. 98, currently in preparation, classifies shiftwork that involves circadian disruption as a probable carcinogenic to humans. in their Exposure circumstances section.

This classification puts circadian disrupting shift work in the same carcinogenic classification as UV radiation exposure from tanning beds, Kaposi's sarcoma herpesvirus/human herpesvirus, inorganic lead compounds, creosotes and diesel engine exhaust.

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

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 florish. 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.

Light-at-night, circadian disruption and breast cancer: assessment of existing evidence

Int. J. Epidemiology, August 2009, Vol. 38, No. 4, p963-970; doi:10.1093/ije/dyp178

Richard G. Stevens

Dept. of Community Medicine, University of Connecticut Health Center, Farmington, CT

Dr. Stevens states that the predictions include

• that non-day shift work would increase risk (in fact the International Agency for Research on Cancer classified shift work as a probable human carcinogen)
• blind women would be at lower risk for breast cancer
• long sleep duration would lower risk
• light level in bedrooms at night would be directly associated with risk
• community nighttime light level would show associations with breast cancer incidence on the population level.

Stevens also points out that one should not just take melatonin as a supplement either. While supplements can beneficially slow the growth of an existing tumor, he points out a study have shown that melatonin can cause a phase shift to their sleeping cycle, thus causing a circadian disruption instead of alleviating it. This is more than just that a person's body clock will shift the time it will want to go to sleep, such as when a person experience jetlag. This may be a small price to pay for an increased protective effect of melatonin, so it would be best to seek the advice of a physician then.

Dr. Stevens has appeared on the CBSNews Morning Show in Nov 30th, 2007 to explain more about this problem.

Here is what I think is very exciting about this, of all the things that we do that can contribute to cancer rates, this is the easiest to correct. There are no gums to chew, patches to wear, daily workout routines to follow, or extra helpings of vegetables to eat to solve this problem. Just turn the lights off until you cannot see your hand. Especially avoid bluish lights. Replace lights that produce glare to that sleep can give you, and some neighbor down the road, all the health effects it can. And let's face it, our schedules are very filled up nowadays. Can we really afford NOT to get the most benefits of what we can out of our sleep time?

A New Possible Link Between Light Pollution and Obesity?

Foodconsumer.org has a page that shows another resulting effect of light pollution -- obesity. They report our biological nights, defined as the period between the onset and cessation of melatonin secretion, shortens due to light pollution. Our bodies then act as if it is Summer All the Time. Meaning that our body clocks evolved to fit the lifestyles of our hunter–gatherer ancestors, who had no artificial lighting. They may have slept less in the longer days of summer, which was also the time for storing up fat reserves for the leaner winter ahead. But in today’s common sleep-deprived, electrified modern lifestyle may be telling our internal clocks it’s summer all the time. Combined with readily available food year-round, and you have a simple precription for substantally increased caloric intakes, and thus greater obesity.

The short sleep durations could be a signal to our metabolic regulatory systems that it’s summertime—it’s time to go out, gain weight, build up fat reserves, to prepare for winter.
-- sleep epidemiologist Jim Gangwisch, University of Columbia

Other sites about the negative health effects of light pollution

Other sites about the negative health effects of light pollution to check out are:

• ScienceNews has been following the problems of light pollution's effects on human health in a series of articles.
• The SkyKeepers.org out in California has their own Light At Night (LAN) and Health page covering additional articles and reports on the effects of lights at night and human health.

When I think about the term "light pollution", I know that it sounds extreme. However, when one considers the damaging effects it causes us and the animals out in the wild, one realizes that light pollution is just as damaging as a toxic chemical spill across the land. The results are almost the same. The difference is that with light pollution, we keep paying for and consuming energy resources, night after night, just to make this pollution, which we could so easily correct if we just put in some effort. In short, stop harming yourself and others in society. Just turn the lights off.