Image copyright Thinkstock 
 
 Even low levels of light in bedrooms may stop breast cancer drugs from working, US researchers have warned. 
 
 Animal tests showed light, equivalent to that from street lamps, could lead to tumours becoming resistant to the widely used drug Tamoxifen. 
 
 The study, published in the journal Cancer Research, showed the light affected sleep hormones, which in turn altered cancer cell function. 
 
 UK experts said it was an intriguing finding, but not proven in people. 
 
 Tamoxifen has transformed the treatment of breast cancer by extending lives and increasing survival times. 
 
 It stops the female hormone oestrogen fuelling the growth of tumours although the cancerous cells may eventually become resistant to the drug. 
 
 Light 
 
 Researchers at the Tulane University School of Medicine investigated the role of the body clock in Tamoxifen resistance. 
 
 They focused their research on the sleep-promoting hormone melatonin, which normally begins to rise in the evening and continues through the night, before falling away as dawn approaches. 
 
 However, light in the evening - such as from a smartphone, tablet or artificial lights - can lower melatonin levels. 
 
 Rats, with human breast cancer and treated with Tamoxifen, were left to sleep in a completely dark cage or one that had dim light. 
 
 The scientists showed that in dim light, melatonin levels were lower, the tumours were bigger and were resistant to Tamoxifen. 
 
 A second set of tests showed that giving those mice melatonin supplements kept Tamoxifen working and resulted in smaller tumours. 
 
 Image copyright Thinkstock 
 
 Dr Steven Hill told the BBC News website: "I'm not advocating people buy melatonin over the counter, there's not enough evidence. 
 
 "But they could make sure they sleep in a room that is completely dark or they could wear eye-masks to let night-time melatonin rise and take Tamoxifen right before going to bed, that would be the easiest way to see if it works." 
 
 Some studies have suggested that melatonin may improve cancer treatments. 
 
 It has been suggested that the hormone calms down cancer cells, which are working on overdrive, to slow down the processes needed to develop resistance. 
 
 Dr Hill wants to move the research into human breast tissue. 
 
 Evening tech 
 
 He did add a warning about using technology, which tends to produce blue light wavelengths that disrupt melatonin production, in the run-up to bedtime. 
 
 "If you get seven hours sleep at night, but use an iPad or computer or watch TV then those blue wavelengths are suppressing melatonin production for anywhere from an hour to an hour and half. 
 
 "So instead of seven hours of melatonin, you're getting six or five and a half." 
 
 Dr Samuel Godfrey, from the charity Cancer Research UK, said: "The link between developing drug-resistant breast cancer and sleeping in dim light is an intriguing one, but it's important that we remember this link was found after studying a small number of rats implanted with breast cancer cells, not humans. 
 
 "More research in people is needed before we know whether the same mechanisms are at work in people." 

 Melatonin 
 
 Other common name(s): none 
 
 Scientific/medical name(s): N-acetyl-5-methoxytryptamine 
 
 Description 
 
 Melatonin is a hormone produced naturally by the pineal gland-- a pea-sized gland located just beneath the center of the brain-- in response to darkness. Melatonin is also available as a man-made supplement. 
 
 Overview 
 
 Research suggests that the melatonin made by the body plays a large role in the daily rhythms of sleeping and waking. Some recent studies have found that people who work night shifts may be at increased risk for cancer, which could be linked to melatonin levels in the body. Study results regarding the effect of melatonin supplements on survival and quality of life in people with cancer have been mixed, and further research in this area is needed. 
 
 How is it promoted for use? 
 
 There is some evidence that melatonin may have a role in the regulation of daily body cycles, sleep patterns, mood, and reproduction. Possible effects on tumor growth and aging are also under study. 
 
 Melatonin is promoted mainly as a sleep aid. Its production in the body may decrease with age, which, according to proponents, may explain why many older people have trouble sleeping. Melatonin is also promoted to help people adjust to odd or irregular work schedules and to counter the effects of jet lag, as it may restore normal sleeping and waking schedules. Some practitioners also believe that melatonin influences hormones in the body that regulate reproduction, the timing of ovulation, and aging. It is sometimes promoted to prevent Alzheimer disease and is often sold as an anti-aging hormone. 
 
 Proponents also claim that melatonin is a powerful anti-oxidant, a compound that blocks the action of free radicals, activated oxygen molecules that can damage cells. Because of melatonin's suspected antioxidant properties, some believe it may suppress the growth of some types of cancer cells, especially when combined with certain anti-cancer drugs. Some supporters suggest that melatonin may also stimulate a type of white blood cell called natural killer cells, which attack tumors. 
 
 Others suggest that melatonin levels and daily body cycles are abnormal in some people with cancer and that melatonin supplements may help them sleep at night. There are also claims that melatonin may decrease the toxic effects of radiation therapy and chemotherapy. 
 
 What does it involve? 
 
 Melatonin is sold as a supplement and is available in drugstores, health food stores, and over the Internet. There are no widely accepted recommendations for dosage or duration of use. Melatonin can also be found in many foods, such as milk, peanuts, almonds, turkey, and chicken, but in such small amounts that one would have to eat very large volumes to obtain a measurable dose. 
 
 What is the history behind it? 
 
 The existence of the pineal gland has been known for thousands of years, although its function remained a mystery until the late 20th century. In the 1600s, the French philosopher René Descartes called the pineal gland "the seat of the soul," because many people believed emotions originated there. 
 
 Researchers at Yale University first discovered melatonin and its connection to the pineal gland in the late 1950s. Its link to sleep and hormonal influences and its possible link to cancer have been studied since that time. Melatonin became available as a dietary supplement in the 1990s. 
 
 What is the evidence? 
 
 Some recent research has suggested that low melatonin levels in the body may be linked to a higher risk of certain types of cancer. For example, a few studies have found that women who work night shifts for many years (and therefore would be expected to have lower levels of melatonin) seem to have a slightly higher risk of breast and colorectal cancer. Even if this research is confirmed, however, it does not necessarily mean that melatonin supplements can lower cancer risk. 
 
 Melatonin has been shown to slow or stop the growth of several types of cancer cells when studied in the laboratory. Whether this same effect occurs in the body is unknown. 
 
 Several studies have looked at the use of melatonin to treat cancer. Melatonin has been used alone and combined with chemotherapy, radiation therapy, hormone therapy (such as tamoxifen), or immunotherapy (such as interleukin-2) in a number of studies involving different types of cancer. Some of the studies have suggested that melatonin may extend survival and improve quality of life for patients with certain types of untreatable cancers such as advanced lung cancer and melanoma. Some studies reported that a small number of cancers went into total or partial remission, while other studies indicated that melatonin caused little or no response in tumors. 
 
 In a 2005 clinical trial looking at cancer-related weight loss (cachexia), melatonin was compared to fish oil in a small group of patients with advanced intestinal cancer. Although neither group gained weight on these substances, three of the eleven patients in the melatonin group did not lose more weight over the 4 week trial period. However, this study was limited by its small size and short period of follow up, and other factors may have accounted for the more stable weight in these patients. 
 
 Most of the studies reporting positive results from melatonin were small and conducted by the same group of Italian researchers. Before the results are widely accepted, they will need to be confirmed in larger studies at other centers. 
 
 Some early studies have reported that melatonin may improve appetite, blood platelet counts, and mouth sores in people undergoing chemotherapy. But a study of melatonin's ability to ease the effects of chemotherapy on the blood counts of lung cancer patients found that high doses of the hormone had little effect. More research is needed to clarify these results. 
 
 There is relatively good evidence that melatonin supplements can influence sleep and fatigue and can help with jet lag and some sleep problems. Research has not yet shown the most effective way to use melatonin supplements for patients with sleep disorders or for people who have trouble sleeping occasionally. Some research shows that melatonin affects not only how quickly people fall asleep but also the duration and quality of sleep. 
 
 Are there any possible problems or complications? 
 
 There appear to be few short-term side effects from taking melatonin. Some people report headaches or feeling drowsy or confused after taking it. People taking high doses have reported nightmares and trouble sleeping. 
 
 The effects of long-term use of melatonin and how it interacts with other medicines or supplements are unknown. Some reports have indicated that melatonin may interact with blood-thinning medicines and with medications for seizures or diabetes. People taking these medicines should speak with their doctors before taking melatonin. 
 
 Since melatonin may have an effect on hormone levels, women who are trying to conceive, are pregnant, or are breast-feeding should not use this supplement. The National Institute on Aging has also warned that melatonin may constrict blood vessels, which could be dangerous for people with high blood pressure or heart disease. Some practitioners believe that children and people under the age of 40 should not take melatonin because their bodies make enough of the hormone naturally. Some also caution people with severe mental illness and those taking steroid medications against using melatonin. 
 
 Because it has antioxidant properties, concerns have been raised that melatonin might interfere with radiation therapy or chemotherapy, possibly making these treatments less effective. While this concern is based largely on theories of how cancer treatments work, it is supported by some recent studies. For this reason, people being treated for cancer should speak with their doctors before taking this supplement. 
 
 Some experts also suggest that people with immune system disorders (such as severe allergies, rheumatoid arthritis, or cancers such as lymphoma) should not take melatonin because it may further stimulate the immune system and worsen these conditions. Again, this is based on a theory and not scientific evidence, but people with immune system problems should speak with their doctors before taking this supplement. 
 
 Relying on this type of treatment alone, and avoiding or delaying conventional medical care for cancer, may have serious health consequences. 
 
 Additional resources 
 
 More information from your American Cancer Society 
 
 The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345). 
 
 Dietary Supplements: What Is Safe? 
 
 The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management 
 
 Complementary and Alternative Methods and Cancer 
 
 Placebo Effect 
 
 Learning About New Ways to Treat Cancer 
 
 Learning About New Ways to Prevent Cancer 
 
 References 
 
 Brzezinski A. Melatonin in humans. N Engl J Med. 1997;336:186-195. 
 
 Cerea G, Vaghi M, Ardizzoia A, et al. Biomodulation of cancer chemotherapy for metastatic colorectal cancer: a randomized study of weekly low-dose irinotecan alone versus irinotecan plus the oncostatic pineal hormone melatonin in metastatic colorectal cancer patients progressing on 5-fluorouracil-containing combinations. Anticancer Res. 2003;23:1951-1954. 
 
 Davis S, Mirick DK. Circadian disruption, shift work and the risk of cancer: a summary of the evidence and studies in Seattle. Cancer Causes Control. 2006;17:539-545. 
 
 Ghielmini M, Pagani O, de Jong J, et al. Double-blind randomized study on the myeloprotective effect of melatonin in combination with carboplatin and etoposide in advanced lung cancer. Br J Cancer. 1999;80:1058-1061. 
 
 Karasek M. Melatonin in humans – Where we are 40 years after its discovery. Neuroendocrinology Letters. 1999;20:179-188. 
 
 Lawenda BD, Kelly KM, Ladas EJ, Sagar SM, Vickers A, Blumberg JB. Should supplemental antioxidant administration be avoided during chemotherapy and radiation therapy? J Natl Cancer Inst. 2008;100:773-783. 
 
 Lissoni P. Is there a role for melatonin in supportive care? Support Care Cancer. 2002;10:110-116. 
 
 Lissoni P, Barni S, Ardizzoia A, Tancini G, Conti A, Maestroni G. A randomized study with the pineal hormone melatonin versus supportive care alone in patients with brain metastases due to solid neoplasms. Cancer. 1994;73:699-701. 
 
 Lissoni P, Chilelli M, Villa S, Cerizza L, Tancini G. Five years survival in metastatic non-small cell lung cancer patients treated with chemotherapy alone or chemotherapy and melatonin: a randomized trial. J Pineal Res. 2003;35:2-15. 
 
 Lissoni P, Paolorossi F, Tancini G, et al. A phase II study of tamoxifen plus melatonin in metastatic solid tumour patients. Br J Cancer. 1996;74:1466-1468. 
 
 Memorial Sloan-Kettering Cancer Center. About herbs: Melatonin. 2006. Accessed at: http://www.mskcc.org/mskcc/html/69298.cfm on June 11, 2008. 
 
 National Institute on Aging. Pills, Patches, and Shots: Can Hormones Prevent Aging? January 2005. Accessed at: http://www.niapublications.org/tipsheets/pills.asp on June 11, 2008. 
 
 M D Anderson Cancer Center. Biologic/Organic/Pharmacologic Therapies: Melatonin. 2005. Accessed at: www.mdanderson.org/departments/cimer/display.cfm?id=90e5bf72-ee9e-463e-bc9ea125d8912312&method=displayfull&pn=6eb86a59-ebd9-11d4-810100508b603a14 on June 11, 2008. 
 
 Persson C, Glimelius B, Ronnelid J, Nygren P. Impact of fish oil and melatonin on cachexia in patients with advanced gastrointestinal cancer: a randomized pilot study. Nutrition. 2005;21:170-178. 
 
 Schernhammer ES, Laden F, Speizer FE, et al. Rotating night shifts and risk of breast cancer in women participating in the Nurses' Health Study. J Natl Cancer Inst. 2001;93:1563-1568. 
 
 Schernhammer ES, Laden F, Speizer FE, et al. Night-shift work and risk of colorectal cancer in the Nurses' Health Study. J Natl Cancer Inst. 2003;95:825–828. 
 
 Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation. 

 The modern bedroom is full of lights, from glowing computer monitors and clock radios to any number of blinking and glimmering electronic devices. Trouble is, chronic exposure to light at night leads to a host of health problems. 
 
 To understand why chronic exposure to light at night is so bad, we need to consider human evolution. Prior to the end of the stone age, humans were exposed to two different kinds of natural light responsible for regulating circadian rhythmicity. During the day we had the sun, while at night we had the moon and the stars, and perhaps the light from campfires. The binary day/night pattern was unrelenting, and our biological programming followed suit. 
 
 Today, we have artificial lighting at night (LAN), and it's a different case altogether. Indoor lighting is considerably less powerful than sunlight, but many orders of magnitude greater than star and moonlight. Check out this chart to see what I mean: 
 
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 Keep in mind that this is a logarithmic scale, so the difference between sunlight and moonlight is considerable — a difference that influences a series of critical biochemical cascades tied to light periodicity, including the production of cortisol and melatonin levels. 
 
 Light is a Drug 
 
 Melatonin suppression is key to understanding much of why LAN is so crappy for us. This workhorse biochemical is produced by the brain's pineal gland at night — when it's dark — to regulate our sleep-wake cycle. It lowers blood pressure, glucose levels, and body temperature — key physiological responses responsible for restful sleep. As neurologist George Brainard puts it, "Light works as if it's a drug, except it's not a drug at all." 
 
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 The part of your brain that controls your biological clock is the Suprachiasmatic Nucleus (SCN), a group of cells in the hypothalamus. These cells respond to light and dark signals. The optic nerves in our eyes senses light and transmits a signal to the SCN telling the brain that it's time to wake up. It also kickstarts other processes, like raising body temperature and producing hormones like cortisol. Our cortisol levels are relatively low at night, allowing us to sleep, and higher during the day, allowing for the stabilization of energy levels and the modulation of immune function. 
 
 But LAN unnaturally elevates cortisol levels at night, which disrupts sleep and introduces a host of problems relating to body-fat levels, insulin resistance, and systemic inflammation. It also contributes to sleep debt and a disruption the neuroregulation of appetite. 
 
 But if our rooms are dark at night, there's no optic signal to the SCN, so our bodies pump out the much needed melatonin. Moreover, our melatonin levels are regulated according to the amount of exposure we had to light during the previous day. 
 
 Related: The science behind power naps and insomnia. 
 
 The Light Before You Sleep 
 
 Indeed, studies have shown that exposure to room light before bedtime shortens melatonin duration by about 90 minutes compared to dim light exposure. In addition, exposure to room light during usual hours of sleep suppresses melatonin levels by more than 50%. That's significant. 
 
 So, even before you hit the hay, the light in your bedroom is causing you problems. With the introduction of tablets, smartphones, and energy-efficient light bulbs, it's an issue that's only getting worse. 
 
 And just to add insult to injury, many modern devices emit blue light from light-emitting diodes (LEDs) — light that's especially good at suppressing melatonin. This is because melanopsin — a photopigment found in specialized cells of the retina involved in the regulation of circadian rhythms — is most sensitive to blue light. 
 
 Recently, scientists warned college students about the impact of light from computer monitors on melatonin levels. They found that computer light at night — particularly blue light that was scanned by wearing different wavelength-blocking glasses — reduces college students' melatonin levels. A related study found that backlit tablet displays suppress melatonin, disrupting sleep. But the researchers write: "[It] is important to acknowledge that usage of self-luminous electronic devices before sleep may disrupt sleep even if melatonin is not suppressed. Clearly, the tasks themselves may be alerting or stressful stimuli that can lead to sleep disruption." Which is a very good point. 
 
 The Cancer Link 
 
 Regrettably, all this hormone and biochemical disruption is creating downstream effects — cancer being one of them. Scientists aren't entirely sure why, but studies consistently show a correlation. 
 
 For example, a 10-year study found that a sample group of over 1,670 women exposed to higher intensity light in their sleeping environment had 22% higher odds of developing breast cancer than those who slept in total darkness. The researchers blamed it on hormone disruption caused by melatonin suppression. 
 
 In another study, researchers implanted nude rats with breast cancer xenografts and then gave them perfusions of blood from different women. Rats receiving blood from women who were exposed to dim light at night had their tumor growth reduced — but those with blood from women who were exposed to bright light at night weren't granted this beneficial effect. 
 
 Troublingly, this has grim implications for workers who do shift work. Case-controlled studies have shown that nurses who work rotating shifts at midnight are more at risk for breast cancer compared to nurses with permanent day work. 
 
 Low Light, Blue Light, Depression and Immune Response 
 
 Disturbingly, the light at night doesn't even have to be bright to cause problems. Chronic exposure to dim light at night leads to depression-like symptom in hamsters, such as exhibiting less interest in drinking the sugar water that they normally love. But by returning them to a normal, non-lit day/night schedule, the researchers were able to reverse the depression. Scientists suspect that this dim-light depression may be the result of a protein called tumor necrosis factor. 
 
 Chronic dim light at night also detrimentally affects the immune system. 
 
 You might want to think about this next time you leave even the dimmest lights on in your bedroom — including your clock radio and the light that bleeds in from street lights. 
 
 Another study, also on rodents, showed that blue light at night in particular is especially powerful at inducing depression-like symptoms. LAN can also impair mood and learning, again likely on account of melanopsin-expressing neurons. 
 
 Premature Aging and Heart Problems 
 
 Melatonin also has antioxidant properties, which plays an important role in anti-aging. Researchers have been able to treat artificially aged mice with melatonin, thus reducing oxidative stress. These mice models are helping scientists understand the fundamental mechanism behind aging because they're the same markers found in neurodegenerative diseases like Alzheimer's. 
 
 Other studies show a link between melatonin suppression and cardiovascular disease. 
 
 Weight Gain 
 
 Light at night also contributes to weight gain by shifting the time of our food intake. Mice, when exposed to LAN, gained more weight — despite exercising and eating as much as their darkness-exposed brethren. Scientists have also correlated low levels of melatonin to diabetes, though it's not clear what role, if any, LAN plays in this matter. 
 
 Pitch Black 
 
 All this research points to one basic fact: We need to keep our bedrooms as dark as possible and avoid blue light before sleep. To that end, you should turn off all your light-emitting gadgets and close the blinds. And if possible, refrain from reading your tablet computer or smartphone in the hours preceding sleep. 
 
 I know, easier said than done. 
 
 Additional reporting by Joseph Bennington-Castro. 
 
 Images: Africa Studio/Shutterstock, MNStudio/Shutterstock. 
 
 Follow me on Twitter: @dvorsky 

 Tamoxifen is an estrogen-blocking medication typically used to treat breast cancer that has spread to other parts of the body. But new research conducted in rats suggests exposure to dim light at night - as little as that coming in a window from a street light - suppresses melatonin production, making tumors resistant to the drug. 
 
 
 
 Researchers found that exposure to dim light at night results in breast cancer tumors becoming resistant to tamoxifen. Researchers found that exposure to dim light at night results intumors becoming resistant to tamoxifen. 
 
 The study, led by Prof. Steven M. Hill of Tulane University School of Medicine in New Orleans, LA, is published in Cancer Research, a journal of the American Association for Cancer Research. 
 
 "Our levels of melatonin are not determined by sleep, as many people think," explains Prof. Hill. "It is actually the darkness that is important. During the night, if you sleep in a brightly lit room, your melatonin levels may be inhibited; however, if you are in the dark but cannot sleep, your melatonin levels will rise normally." 
 
 He and his team note that disruption of circadian rhythms by night shift work or disturbed sleep could result in an increased risk of breast cancer and other diseases. For patients with hormone receptor-positive breast cancer, Prof. Hill adds that tamoxifen resistance "is a growing problem." 
 
 "Our data, although they were generated in rats, have potential implications for the large number of patients with breast cancer who are being treated with tamoxifen, because they suggest that nighttime exposure to light, even dim light, could cause their tumors to become resistant to the drug by suppressing melatonin production," he says. 
 
 Nighttime melatonin supplement resulted in regressed tumors 
 
 To conduct their study, the researchers observed rats with human breast tumors that were living in either normal light and dark conditions - which involved 12 hours of light and 12 hours of complete darkness - or alternative conditions - 12 hours of normal light and 12 hours of dim light. 
 
 Fast facts about tamoxifen's uses To treat breast cancer that has spread to other parts of the body 
 
 To treat early breast cancer in women who have already been treated with surgery, radiation or chemotherapy 
 
 To reduce risk of developing a more serious type of breast cancer in women who have had ductal carcinoma in situ 
 
 To reduce risk of breast cancer in women at high risk for the disease. 
 
 The rats who were living under normal conditions had blood melatonin levels that rose during the dark period and fell again during the light period. However, the rats living in the alternative conditions had melatonin levels that remained low during the light/dark cycle. 
 
 Compared with the rats living in normal conditions, the rats living in the dim night light conditions had tumor growth that was 2.6-fold times faster. 
 
 Additionally, the team found that the rats living in the dim night light had tumors that were completely resistant to tamoxifen, while the rats living in normal conditions had tumors that significantly regressed. 
 
 However, the team also found that when given a nighttime melatonin supplement, the tumors of the rats living in dim night light conditions likewise regressed. 
 
 "These data suggest that, in the not-too-distant future, it may be possible to combine melatonin and tamoxifen," says Prof. Hill. "However, before this is done we would need to identify the optimal times of day to give the two because if the timing between the two is off, the advantage of giving them in combination may be lost." 
 
 He also notes that their study does not reveal how much light exposure is needed to decrease nighttime melatonin production, resulting in tamoxifen resistance in humans, "but we think that it could be as little as the amount of light that comes in the bedroom window from a street light." 
 
 Though melatonin supplements can be purchased over the counter, Prof. Hill cautions that their research is not yet at the point where he and his team can recommend that breast cancer patients on tamoxifen take melatonin: 
 
 "Melatonin is produced by our bodies at a very specific time of day, exclusively during darkness at night, and taking melatonin supplements at the wrong time of day would potentially disrupt the circadian system, particularly the natural melatonin cycle, which may, in itself, paradoxically impair breast cancer responsiveness to tamoxifen." 
 
 The team is now conducting further studies to investigate how much light exposure suppresses nighttime melatonin production in humans to the point where it would make tumors tamoxifen-resistant. 
 
 Medical News Today recently reported on a study that suggested the gel form of tamoxifen is just as effective as the oral form, with fewer side effects.
– Light at night has already been widely linked to poorer sleep quality, but now even dim light is being shown to interfere with a breast cancer drug's ability to do its job. So says a new study on rats out of Tulane University School of Medicine, which found that even the low light of a nearby street lamp interferes with the body's natural production of the sleep hormone melatonin. And the rats (all of which had human breast tumors) exposed to dim light at night not only exhibited lower levels of melatonin but had larger, faster-growing tumors that were also completely resistant to the breast cancer drug Tamoxifen. "Our levels of melatonin are not determined by sleep, as many people think," one researcher tells Medical News Today. "It is actually the darkness that is important." And he tells the BBC that the blue light emitted from digital devices such as TVs and tablets is particularly disruptive for melatonin production. Other studies have suggested that melatonin may help improve cancer treatments. Still, researchers warn that this study needs to be replicated and validated in humans before determining that all the same mechanisms are at play. (City lights have also been linked to higher breast cancer rates.)