Abstracts of Recent Peer Reviewed Journal Articles (from MedLine).

1. Authors: Schernhammer ES. Schulmeister K.
Institution: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA 02115, USA. eva.schernhammer@channing.harvard.edu
Title: Melatonin and cancer risk: does light at night compromise physiologic cancer protection by lowering serum melatonin levels?. [Review] [42 refs]
Source: British Journal of Cancer. 90(5):941-3, 2004 Mar 8.

The suprachiasmatic nuclei in the hypothalamus, one of the most important physiological determinants of alertness and performance, drive a circadian pacemaker in mammals, with an intrinsic period averaging 24 h. Light is the primary stimulus to the disruption and resetting of this pacemaker, which is expressed in changing melatonin rhythms. Melatonin production in humans decreases when people are exposed to light at night. Since melatonin shows potential oncostatic action in a variety of tumours, it is possible that lowered serum melatonin levels caused by exposure to light at night enhance the general tumour development. Cancer is the second leading cause of death in industrialised countries like the United States, where a significant proportion of workers engage in shift work, making a hypothesised relation between light exposure at night and cancer risk relevant. Observational studies support an association between night work and cancer risk. We hypothesis that the potential primary culprit for this observed association is the lack of melatonin, a cancer-protective agent whose production is severely diminished in people exposed to light at night. [References: 42]

2. Authors: Schernhammer E. Schulmeister K.
Institution: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. eva.schernhammer@channing.harvard.edu
Title: Light at night and cancer risk. [Review] [19 refs]
Source: Photochemistry & Photobiology. 79(4):316-8, 2004 Apr.

Abstract Environmental lighting powerfully suppresses the physiologic release of melatonin, which typically peaks in the middle of the night. This decreased melatonin production has been hypothesized to increase the risk of cancer. Evidence from experimental studies supports a link between melatonin and tumor growth. There is also fairly consistent indirect evidence from observational studies for an association between melatonin suppression, using night work as a surrogate, and breast cancer risk. [References: 19]

3. Authors: Blask DE. Dauchy RT. Sauer LA. Krause JA. Brainard GC.
Institution: Laboratory of Chrono-Neuroendocrine Oncology, Bassett Research Institute, Cooperstown, NY 13326, USA. david.blask@bassett.org
Title: Growth and fatty acid metabolism of human breast cancer (MCF-7) xenografts in nude rats: impact of constant light-induced nocturnal melatonin suppression.
Source: Breast Cancer Research & Treatment. 79(3):313-20, 2003 Jun.

Abstract The nocturnal melatonin (MLT) surge is a relevant oncostatic signal for a variety of experimental malignancies. Population studies support the hypothesis that exposure to light at night may represent a new risk factor for breast cancer possibly through the suppression of pineal MLT production and/or circadian disruption. We tested the ability of constant light exposure to suppress MLT production in female nude rats and stimulate the growth of tissue-isolated MCF-7 human breast cancer xenografts via increased tumor linoleic acid (LA) metabolism. Rats maintained on an alternating light/dark cycle (L:D group) exhibited a robust circadian MLT rhythm that was abolished following constant light exposure. During the exposure of animals bearing tissue-isolated human MCF-7 breast cancer xenografts to constant light, the rate of tumor growth markedly increased relative to the L:D group. Tumor LA uptake and its metabolism to the mitogen 13-hydroxyoctadecadienoic acid (13-HODE) were also substantially higher under constant light conditions. This is the first biological evidence for a potential link between constant light exposure and increased human breast oncogenesis involving MLT suppression and stimulation of tumor LA metabolism.

4. Authors: Glickman G. Levin R. Brainard GC. Brainard GC.
Investigator: Brainard GC.
Institution: Department of Neurology, Jefferson Medical College, 1015 Walnut Street, Philadelphia, PA 19107, USA. gxg001@jefferson.edu
Investigator Affiliation: Thomas Jefferson U, Philadelphia, PA
Title: Ocular input for human melatonin regulation: relevance to breast cancer. [Review] [64 refs]
Source: Neuroendocrinology Letters. 23 Suppl 2:17-22, 2002 Jul.

Abstract The impact of breast cancer on women across the world has been extensive and severe. As prevalence of breast cancer is greatest in industrialized regions, exposure to light at night has been proposed as a potential risk factor. This theory is supported by the epidemiological observations of decreased breast cancer in blind women and increased breast cancer in women who do shift-work. In addition, human, animal and in vitro studies which have investigated the melatonin-cancer dynamic indicate an apparent relationship between light, melatonin and cancer, albeit complex. Recent developments in understanding melatonin regulation by light in humans are examined, with particular attention to factors that contribute to the sensitivity of the light-induced melatonin suppression response. Specifically, the role of spectral characteristics of light is addressed, and recent relevant action spectrum studies in humans and other mammalian species are discussed. Across five action spectra for circadian and other non-visual responses, a peak sensitivity between 446-484 nm was identified. Under highly controlled exposure circumstances, less than 1 lux of monochromatic light elicited a significant suppression of nocturnal melatonin. In view of the possible link between light exposure, melatonin suppression and cancer risk, it is important to continue to identify the basic related ocular physiology. Visual performance, rather than circadian function, has been the primary focus of architectural lighting systems. It is now necessary to reevaluate lighting strategies, with consideration of circadian influences, in an effort to maximize physiological homeostasis and health. [References: 64]

5. Authors: Reiter RJ.
Institution: Department of Cellular and Structural Biology, The University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA. reiter@uthscsa.edu
Title: Potential biological consequences of excessive light exposure: melatonin suppression, DNA damage, cancer and neurodegenerative diseases.[see comment]. [Review] [62 refs]
Comment in: Neuro Endocrinol Lett. 2002 Oct-Dec;23(5-6):385-6; PMID: 12500157
Source Neuroendocrinology Letters. 23 Suppl 2:9-13, 2002 Jul.

Abstract This brief review summarizes some of the biological effects of light exposure at an inappropriate time (during the normal dark period) and the potential negative physiological consequences of this light exposure. Two major systems are significantly influenced by light at night. Thus, the circadian system and melatonin synthesis are altered when light is extended into the normal dark period or when the dark period is interrupted by light. This summary reviews the potential sequelae of chronic inappropriate light exposure and the suppression of endogenous melatonin levels. Given that melatonin is a free radical scavenger and antioxidant, conditions that involve free radical damage may be aggravated by light suppression of melatonin levels. The conditions of particular interest for this review are excessive DNA damage (which potentially leads to cancer), cellular destruction in neurodegenerative diseases and aging itself. Further research should be conducted to more accurately define the potential negative impact of light at abnormal times on animal and human athophysiology. [References: 62]

6. Status: In-Process
Authors: Pauley SM.
Institution: spauley@cox-internet.com
Title: Lighting for the human circadian clock: recent research indicates that lighting has become a public health issue.
Source: Medical Hypotheses. 63(4):588-96, 2004.

Abstract The hypothesis that the suppression of melatonin (MLT) by exposure to light at night (LAN) may be one reason for the higher rates of breast and colorectal cancers in the developed world deserves more attention. The literature supports raising this subject for awareness as a growing public health issue. Evidence now exists that indirectly links exposures to LAN to human breast and colorectal cancers in shift workers. The hypothesis begs an even larger question: has medical science overlooked the suppression of MLT by LAN as a contributor to the overall incidence of cancer? The indirect linkage of breast cancer to LAN is further supported by laboratory rat experiments by David E. Blask and colleagues. Experiments involved the implanting of human MCF-7 breast cancer cell xenografts into the groins of rats and measurements were made of cancer cell growth rates, the uptake of linoleic acid (LA), and MLT levels. One group of implanted rats were placed in light-dark (12L:12D) and a second group in light-light (12L:12L) environments. Constant light suppressed MLT, increased cancer cell growth rates, and increased LA uptake into cancer cells. The opposite was seen in the light-dark group. The proposed mechanism is the suppression of nocturnal MLT by exposure to LAN and subsequent lack of protection by MLT on cancer cell receptor sites which allows the uptake of LA which in turn enhances the growth of cancer cells. MLT is a protective, oncostatic hormone and strong antioxidant having evolved in all plants and animals over the millennia. In vertebrates, MLT is normally produced by the pineal gland during the early morning hours of darkness, even in nocturnal animals, and is suppressed by exposure to LAN. Daily entrainment of the human circadian clock is important for good human health. These studies suggest that the proper use and color of indoor and outdoor lighting is important to the health of both humans and ecosystems. Lighting fixtures should be designed to minimize interference with normal circadian rhythms in plants and animals. New discoveries on blue-light-sensitive retinal ganglion cell light receptors that control the circadian clock and how those receptors relate to today's modern high intensity discharge (HID) lamps are discussed. There is a brief discussion of circadian rhythms and light pollution. With the precautionary principle in mind, practical suggestions are offered for better indoor and outdoor lighting practices designed to safeguard human health. Copyright 2004 Elsevier Ltd.

7. Authors: Poole C.
Institution: Department of Epidemiology (CB 7435), University of North Carolina School of Public Health, Chapel Hill, NC 27599-7435, USA. cpoole@unc.edu
Title: The darkness at the end of the tunnel: summary and evaluation of an international symposium on light, endocrine systems and cancer. [Review] [26 refs]
Source: Neuroendocrinology Letters. 23 Suppl 2:71-8, 2002 Jul.

Abstract Research on light at night and cancer is evolving at an accelerating pace, fueled largely by exciting results in rodent toxicology and basic human biology. Epidemiologic research is at a relatively early stage of development in which the exposure surrogates such as shift work and blindness predominate. Causal graphs for shift work, light at night and breast cancer illustrate some of the subtleties that can arise in the use of exposure surrogates of different kinds. Baseline data on circadian rhythms and melatonin cycles among human populations living at different latitudes are needed. Epidemiologic study of this topic is expected to mature soon as studies begin to incorporate quantitative and semiquantitative measurements and personal histories of exposure to light at night. The current emphasis on breast cancer should widen to include other cancers and intermediate outcomes. An advance in epidemiologic studies of blind persons would be to compare cancer rates between the "cortically blind" and the "retinally blind" within levels of visual impairment. Without a proposed intervention to reduce exposure to light at night, attributable fraction and attributable caseload estimates are meaningless. In the near future, both epidemiologic and laboratory research in this area are expected to grow appreciably in scope and scale. [References: 26]

8. Unique Identifier 11604479
Authors Davis S. Mirick DK. Stevens RG.
Institution Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024, USA. sdavis@fhcrc.org
Title Night shift work, light at night, and risk of breast cancer.[see comment].
Comments Comment in: J Natl Cancer Inst. 2001 Oct 17;93(20):1513-5; PMID: 11604468, Comment in: J Natl Cancer Inst. 2002 Apr 3;94(7):530-1; author reply 533; PMID: 11929956, Comment in: J Natl Cancer Inst. 2002 Apr 3;94(7):530; author reply 532-3; PMID: 11929957, Comment in: J Natl Cancer Inst. 2002 Apr 3;94(7):531-2; author reply 533-4; PMID: 11929958
Source Journal of the National Cancer Institute. 93(20):1557-62, 2001 Oct 17.

Abstract BACKGROUND: 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 shiftwork 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 shiftwork (P =.02, Wald chi-squared test). CONCLUSION: 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.

9. Unique Identifier 11581092
Authors Davis S. Kaune WT. Mirick DK. Chen C. Stevens RG.
Institution Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109-1024, USA. sdavis@fhcrc.org
Title Residential magnetic fields, light-at-night, and nocturnal urinary 6-sulfatoxymelatonin concentration in women.
Source American Journal of Epidemiology. 154(7):591-600, 2001 Oct 1.

Abstract Exposure to 60-Hz magnetic fields may increase breast cancer risk by suppressing the normal nocturnal rise in melatonin. This 1994-1996 Washington State study investigated whether such exposure was associated with lower nocturnal urinary concentration of 6-sulfatoxymelatonin in 203 women aged 20-74 years with no history of breast cancer. Each woman was interviewed and provided data on the following for a 72-hour period at two different seasons of the year: 1) magnetic field and ambient light measured every 30 seconds in her bedroom, 2) personal magnetic field measured at 30-second intervals, and 3) complete nighttime urine samples on three consecutive nights. Lower nocturnal urinary 6-sulfatoxymelatonin level was associated with more hours of daylight, older age, higher body mass index, current alcohol consumption, and current use of medications classified as beta blockers, calcium channel blockers, or psychotropics. After adjustment for these factors, higher bedroom magnetic field level was associated with significantly lower urinary concentration of 6-sulfatoxymelatonin during the same night, primarily in women who used these medications and during times of the year with the fewest hours of darkness. These results suggest that exposure to nighttime residential 60-Hz magnetic fields can depress the normal nocturnal rise in melatonin.

10. Unique Identifier 11377374
Authors Sauer LA. Dauchy RT. Blask DE.
Institution Bassett Research Institute, The Mary Imogene Bassett Hospital, Cooperstown, NY 13326, USA. lensauer@juno.com
Title Polyunsaturated fatty acids, melatonin, and cancer prevention. [Review] [61 refs]
Source Biochemical Pharmacology. 61(12):1455-62, 2001 Jun 15.

Abstract Many nutritional, hormonal, and environmental factors affect carcinogenesis and growth of established tumors in rodents. In some cases, these factors may either enhance or attenuate the neoplastic process. Recent experiments performed in our laboratory using tissue-isolated rat hepatoma 7288CTC in vivo or during perfusion in situ have demonstrated new interactions among four of these factors. Two agents, dietary linoleic acid (C18:2n6) and "light at night," enhanced tumor growth, and two others, melatonin and n3 fatty acids, attenuated growth. Linoleic acid stimulated tumor growth because it is converted by hepatoma 7288CTC to the mitogen, 13-hydroxyoctadecadienoic acid (13-HODE). Melatonin, the neurohormone synthesized and secreted at night by the pineal gland, and dietary n3 fatty acids are potent antitumor agents. Both inhibited tumor linoleic acid uptake and 13-HODE formation. Artificial light, specifically "light at night," increased tumor growth because it suppressed melatonin synthesis and enhanced 13-HODE formation. Melatonin and n3 fatty acids acted via similar or identical G(i) protein-coupled signal transduction pathways, except that melatonin receptors and putative n3 fatty acid receptors were used. The results link the four factors in a common mechanism and provide new insights into the roles of dietary n6 and n3 polyunsaturated fatty acid intake, "light at night," and melatonin in cancer prevention in humans. [References: 61]

11. Unique Identifier 11215676
Authors Travlos GS. Wilson RE. Murrell JA. Chignell CF. Boorman GA.
Institution Laboratory of Experimental Pathology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA. travlos@niehs.nih.gov
Title The effect of short intermittent light exposures on the melatonin circadian rhythm and NMU-induced breast cancer in female F344/N rats.
Source Toxicologic Pathology. 29(1):126-36, 2001 Jan-Feb.
Abstract We investigated the effects of altered endogenous nighttime melatonin concentrations on mammary tumor production in an N-nitroso-N-methylurea (NMU)-induced breast cancer model in female Fischer 344 (F344)/N rats. Experiments were designed 1) to evaluate whether short-duration intermittent exposures to light at night would affect the nocturnal rise of melatonin, resulting in a decrease in nighttime serum melatonin concentrations, 2) to evaluate whether any suppression of nighttime serum melatonin concentrations could be maintained for a period of weeks, and 3) to determine the effects of suppressed serum melatonin concentrations on the incidence and progression of NMU-induced breast cancer. In vivo studies were used to assess serum melatonin concentrations after 1 day and 2 and 10 weeks of nightly administration of short-duration intermittent light exposure at night and incidence of NMU-induced tumors. Five 1-minute exposures to incandescent light every 2 hours after the start of the dark phase of the light: dark cycle decreased the magnitude of the nocturnal rise of serum melatonin concentrations in rats by approximately 65%. After 2 weeks of nightly intermittent light exposures, an average decrease of the peak nighttime serum melatonin concentrations of approximately 35% occurred. The amelioration continued and, at 10 weeks, peak nighttime serum melatonin concentrations were still decreased, by approximately 25%. Because peak endogenous nighttime serum melatonin values could be moderately suppressed for at least 10 weeks, a 26-week NMU mammary tumor study was conducted. Serum melatonin concentrations and incidence, multiplicity, and weight of NMU-induced mammary tumors were assessed. A group of pinealectomized (Px) animals was also included in the tumor study. No effect on the development of mammary tumors in an NMU-induced tumor model in rats occurred when endogenous nighttime serum melatonin concentrations were moderately suppressed by short-duration intermittent light exposures at night. At necropsy, there were no alterations in mammary tumor incidence (28/40 NMU controls, 28/40 NMU + light, 31/40 NMU + Px), multiplicity (2.18 tumors/tumor-bearing NMU control, 1.89 NMU + light, 2.39 NMU + Px), or average tumor weight (1.20 g NMU control, 1.19 g NMU + light, 0.74 g NMU + Px). Tumor burden had no effect on the serum melatonin cycle. At 26 weeks, however, animals exposed to intermittent light at night exhibited approximately 3-fold higher serum melatonin concentrations as compared with controls. Additionally, rats that had been pinealectomized at 4 weeks of age had serum melatonin concentrations that were markedly higher than the expected baseline concentrations for pinealectomized rats (<15 pg/ml), suggesting the reestablishment of a melatonin cycle. This finding was unexpected and suggests that melatonin can be produced by an organ or tissue other than the pineal gland.

12. Unique Identifier 10100735
Authors Brainard GC. Kavet R. Kheifets LI.
Institution Department of Neurology, Jefferson Medical College, Philadelphia, Pennsylvannia 19107, USA. george.brainardemail.tju.edu.
Title The relationship between electromagnetic field and light exposures to melatonin and breast cancer risk: a review of the relevant literature. [Review] [210 refs]
Source Journal of Pineal Research. 26(2):65-100, 1999 Mar.

Abstract Worldwide, breast cancer is the most common malignancy accounting for 20-32% of all female cancers. This review summarizes the peer-reviewed, published data pertinent to the hypothesis that increased breast cancer in industrialized countries is related to the increased use of electricity [Stevens, R.G., S. Davis 1996]. That hypothesis specifically proposes that increased exposure to light at night and electromagnetic fields (EMF) reduce melatonin production. Because some studies have shown that melatonin suppresses mammary tumorigenesis in rats and blocks estrogen-induced proliferation of human breast cancer cells in vitro, it is reasoned that decreased melatonin production leads to increased risk of breast cancer. To evaluate this hypothesis, the paper reviews epidemiological data on associations between electricity and breast cancer, and assesses the data on the effects of EMF exposure on melatonin physiology in both laboratory animals and humans. In addition, the results on the effects of melatonin on in vivo carcinogenesis in animals are detailed along with the controlled in vitro studies on melatonin's effects on human breast cancer cell lines. The literature is evaluated for strength of evidence, inter-relationships between various lines of evidence, and gaps in our knowledge. Based on the published data, it is currently unclear if EMF and electric light exposure are significant risk factors for breast cancer, but further study appears warranted. Given the ubiquitous nature of EMF and artificial light exposure along with the high incidence of breast cancer, even a small risk would have a substantial public health impact. [References: 210]

13. Unique Identifier 8722117
Authors Stevens RG. Davis S.
Institution Pacific Northwest Laboratory, Richland, Washington 99352, USA. bougs@pnl.gov
Title The melatonin hypothesis: electric power and breast cancer. [Review] [66 refs]
Source Environmental Health Perspectives. 104 Suppl 1:135-40, 1996 Mar.

Abstract Breast cancer is a disease of modern life. As societies industrialize, risk increases, yet it is unclear which of the myriad changes coming with industrialization drives this increase. One important hallmark of modern life is the pervasive use of electric power. Electric power produces light at night (LAN) and electric and magnetic fields (EMF), either or both of which may alter pineal function and its primary hormone melatonin, thereby, perhaps increasing the risk of breast cancer. This hypothesis, stated a decade ago, is now receiving considerable experimental and epidemiological attention. The circumstantial case for the hypothesis has three aspects: light effects on melatonin, EMF effects on melatonin, and melatonin effects on breast cancer. The strongest of these aspects is the effects of light on melatonin. It is clear that the normal nocturnal melatonin rise in humans can be suppressed by light of sufficient intensity. The evidence for an effect of melatonin on breast cancer in experimental animals is strong, but the evidence in humans is scant and difficult to gather. The weakest aspect of the circumstantial case is EMF effects on melatonin. Whereas a half dozen independent laboratories have published findings of suppression in animals, there are inconsistencies, and there are no published data on humans. The direct evidence bearing on the hypothesis is sparse but provocative. Two laboratories have published data showing substantial increases in chemically induced breast cancer in rats by a weak AC (alternating current) magnetic field. The epidemiological evidence is very limited but has offered some support as well. An effect of electric power on breast cancer would have profound implications, and this possibility deserves continued investigation. [References: 66]

14. Unique Identifier 12163844
Authors Lerchl A.
Institution School of Engineering and Science, International University Bremen, Campus Ring 1, D-28759 Bremen, Germany. a.lerchl@iu-bremen.de
Title Biological rhythms in the context of light at night (LAN). [Review] [15 refs]
Source Neuroendocrinology Letters. 23 Suppl 2:23-7, 2002 Jul.

Abstract In mammals including man, the most important zeitgeber for endogenous rhythms is the environmental light/dark cycle. Mammals perceive light through the eyes and that perception is relayed to the suprachiasmatic nucleus (SCN) by means of neuronal signals. The SCN, in turn, innervates the pineal gland, resulting in the production and release of melatonin almost exclusively during night-time hours. Thus, besides object recognition, eyes serve as the sensory organ for detecting the presence or absence of light. The way that light entrains the SCN is still a matter of intense research. It has been shown, for example, that the light intensities required for affecting melatonin rhythms are much higher than the intensities needed for object identification. On the other hand, even in rodents who completely lack the "classical" photoreceptors of the retina, their endogenous rhythms still can be synchronized by normal light/dark cycles. These two observations led to the hypothesis that there must be photoreceptors, apart from the known (object-identifying) retinal photoreceptors, which are responsible for the entrainment of internal rhythms. Very recently, a number of reports showed that in fact a completely new type of retinal photoreceptor, located in ganglion cells, may be responsible for entraining the SCN. It contains a photopigment, melanopsin, which shares homologies with rhodopsin, but also is evolutionarily older. Compared to rods or cones, the melanopsin-containing neurons are rare, but evenly distributed within the retina, indicating that they serve as a global, integrating light sensor. These ganglion cells apparently project directly into the SCN. Taken together, these new developments in photo-chronobiology open new areas of research. It will be of special interest, for example, to determine how the photosensitive ganglion cells and their dendrites integrate the environmental light stimuli. [References: 15]

15. Unique Identifier 12568246
Authors Glickman G. Hanifin JP. Rollag MD. Wang J. Cooper H. Brainard GC. Brainard GC.
Investigator: Brainard GC.
Institution Department of Neurology, Jefferson Medical College, Philadelphia, PA 19107, USA. gxg001@jefferson.edu
Investigator Affiliation: Jefferson Med Coll, Philadelphia, PA
Title Inferior retinal light exposure is more effective than superior retinal exposure in suppressing melatonin in humans.
Source Journal of Biological Rhythms. 18(1):71-9, 2003 Feb.

Abstract Illumination of different areas of the human retina elicits differences in acute light-induced suppression of melatonin. The aim of this study was to compare changes in plasma melatonin levels when light exposures of equal illuminance and equal photon dose were administered to superior, inferior, and full retinal fields. Nine healthy subjects participated in the study. Plexiglass eye shields were modified to permit selective exposure of the superior and inferior halves of the retinas of each subject. The Humphrey Visual Field Analyzer was used both to confirm intact full visual fields and to quantify exposure of upper and lower visual fields. On study nights, eyes were dilated, and subjects were exposed to pattern less white light for 90 min between 0200 and 0330 under five conditions: (1) full retinal exposure at 200 lux, (2) full retinal exposure at 100 lux, (3) inferior retinal exposure at 200 lux, (4) superior retinal exposure at 200 lux, and (5) a dark-exposed control. Plasma melatonin levels were determined by radioimmunoassay. ANOVA demonstrated a significant effect of exposure condition (F = 5.91, p < 0.005). Post hoc Fisher PLSD tests showed significant (p < 0.05) melatonin suppression of both full retinal exposures as well as the inferior retinal exposure; however, superior retinal exposure was significantly less effective in suppressing melatonin. Furthermore, suppression with superior retinal exposure was not significantly different from that of the dark control condition. The results indicate that the inferior retina contributes more to the light-induced suppression of melatonin than the superior retina at the photon dosages tested in this study. Findings suggest a greater sensitivity or denser distribution of photoreceptors in the inferior retina are involved in light detection for the retinohypothalamic tract of humans.

16. Unique Identifier 9756329
Authors Aoki H. Yamada N. Ozeki Y. Yamane H. Kato N.
Institution Department of Psychiatry, Shiga University of Medical Science, Otsu, Japan.
Title Minimum light intensity required to suppress nocturnal melatonin concentration in human saliva.
Source Neuroscience Letters. 252(2):91-4, 1998 Aug 14.

Abstract We set out to determine the minimum intensity of light able to suppress nocturnal melatonin levels as measured in normal human saliva. Five healthy male volunteers were exposed to light at different intensities (<10, 500, 1000, 2500, and 5000 lux) in a repeated measure design. Suppression of melatonin was dependent on both light intensity and duration of light exposure. Minimum intensities of light suppressing nocturnal melatonin levels were calculated as 393, 366, 339, and 285 lux for exposure durations of 30, 60, 90, and 120 min, respectively. Minimum effective intensity and duration of light exposure showed a linear inverse relationship. These results suggest that less intensity of light than previously reported suffices to suppress melatonin in humans, and that caution is required in interpreting studies using long exposure to dim light as a background condition.