Abstract
Light controls pineal melatonin production and temporally coordinates circadian rhythms of metabolism and physiology in normal and neoplastic tissues. We previously showed that peak circulating nocturnal melatonin levels were 7-fold higher after daytime spectral transmittance of white light through blue-tinted (compared with clear) rodent cages. Here, we tested the hypothesis that daytime blue-light amplification of nocturnal melatonin enhances the inhibition of metabolism, signaling activity, and growth of prostate cancer xenografts. Compared with male nude rats housed in clear cages under a 12:12-h light:dark cycle, rats in blue-tinted cages (with increased transmittance of 462-484 nm and decreased red light greater than 640 nm) evinced over 6-fold higher peak plasma melatonin levels at middark phase (time, 2400), whereas midlight-phase levels (1200) were low (less than 3 pg/mL) in both groups. Circadian rhythms of arterial plasma levels of linoleic acid, glucose, lactic acid, pO2, pCO2, insulin, leptin, and corticosterone were disrupted in rats in blue cages as compared with the corresponding entrained rhythms in clear-caged rats. After implantation with tissue-isolated PC3 human prostate cancer xenografts, tumor latency-to-onset of growth and growth rates were markedly delayed, and tumor cAMP levels, uptake-metabolism of linoleic acid, aerobic glycolysis (Warburg effect), and growth signaling activities were reduced in rats in blue compared with clear cages. These data show that the amplification of nighttime melatonin levels by exposing nude rats to blue light during the daytime significantly reduces human prostate cancer metabolic, signaling, and proliferative activities.
https://pubmed.ncbi.nlm.nih.gov/26678364/
Kræft
Kræft er betegnelsen for celler i kroppen, der deles ukontrolleret. Cellerne ændrer karakter på grund af mutationer i deres arvemateriale og vil efterfølgende spredes til det omgivende væv og derefter spredes til andre steder i kroppen gennem blodet. Kræftcellerne hæmmer de normale celler, og uden behandling kan kræft til sidst føre til døden. I dag findes der mange behandlingsmetoder i den medicinske verden og behandlingerne bliver hele tiden bedre.
Beskrivelse
Der er mange former for kræft, og kræftens gåde er langt fra løst. Men noget tyder stærkt på, at der er en sammenhæng mellem kræft, lys og melatonin.
Kræft og lys
Hvis der ikke var kunstigt lys på jorden, ville vi mennesker være omgivet af mørke i gennemsnitligt 12 timer hvert døgn.
Forsøg ved Harvard University har påvist, at blinde mennesker, som jo altid oplever mørke, producerer melatonin 9-10 timer om natten. Blinde har samtidig 50 % lavere risiko for at udvikle kræft sammenlignet med normaltseende.
På grund af kunstig belysning er de fleste mennesker i den vestlige verden kun omgivet af mørke i ca. 7-8 timer om natten. Det reducerer den natlige produktion af melatonin til 6-7 timer.
Mange forskellige undersøgelser på både dyr og mennesker peger på en sammenhæng mellem kunstigt lys og kræft. I et dyreforsøg voksede tumorer fx hurtigt hos dyr opvokset i et miljø med korte nætter og høj kunstig belysning, mens tumorer holdt op med at vokse eller voksede langsomt hos dyr opvokset med lange nætter og mindre kunstig belysning.
Brug af kunstig belysning reducerer varigheden af melatoninproduktionen og tilstedeværelsen af melatonin i blodet. Undersøgelser af primitive samfund, som er omgivet af længere perioder med mørke, da de ikke har kunstig belysning, har påvist en meget lavere forekomst af kræft. Der er selvfølgelig andre variabler, når man sammenligner moderne kulturer med primitive kulturer, men den voksende mængde af dokumentationer peger på en sammenhæng mellem brugen af kunstig belysning og øgede sundhedsrisici.
Melatonin er ikke det eneste stof, der produceres i koglekirtlen, som er ret komplekst. Det er endnu ikke endeligt afgjort, om disse andre stoffer også spiller en væsentlig rolle i kampen mod kræft. Dette kan være årsagen til, at det at tage melatonin-tabletter ikke ser ud til at være lige så effektivt til at bekæmpe kræftceller som kroppens eget naturligt producerede melatonin.
Da det virker usandsynligt, at vi i den nærmeste fremtid vil opgive elektrisk belysning, er det især opmuntrende at vide, at forskere i 2002 opdagede, at det ikke er alt lyset i lysspektret, der hæmmer produktionen af melatonin. Det er det blå lys i det synlige lysspektrum, der forårsager hæmning af melatonin. Du kan løse problemet ved at blokere for det blå lys. Du kan bruge belysning, der filtrerer det blå lys fra til praktisk brug, fx til at læse, se TV eller når du arbejder på en computer. Denne dynamik blev for første gang demonstreret på University of Toronto, da forsøgspersoner simulerede natarbejde, mens de bar specielle briller, der blokerede alt blåt lys. Forsøgspersonerne producerede melatonin, selvom de befandt sig i stærkt oplyste omgivelser.
Melatonin og kræft generelt
Der er meget evidens for, at melatonin har en beskyttende effekt i mange kræftsammenhænge:
Melatonin styrker kroppens immunforsvar.
Melatonin styrker cellernes evne til at ødelægge sig selv, hvis de er blevet beskadiget. En beskadiget celle kan udvikle sig til en kræftcelle.
Melatonin er som antioxidant med til at beskytte kroppens celler og væv mod frie radikaler, som dannes, når ilt omdannes til energi i kroppen. De frie radikaler kan beskadige cellerne og bidrage til udviklingen af sygdomme, herunder kræft.
Melatonin reducerer muligvis de skadelige bivirkninger af strålebehandling og kemoterapi.
Melatonin reducerer muligvis produktionen af østrogen, som nogle kræftformer er afhængige af.
Melatonin og brystkræft
Der er gennemført en lang række undersøgelser, som påviser en bemærkelsesværdig sammenhæng mellem natarbejde/skiftearbejde og forskellige former for kræft.
Hos Kræftens Bekæmpelse i Danmark har man for eksempel undersøgt, om der er øget risiko for brystkræft blandt kvinder, der har aften- og natarbejde.
Undersøgelsen er foretaget blandt danske kvinder i alderen 30-54 år og viser, at risikoen for brystkræft stiger med op til 40 % blandt kvinder, der arbejder om aftenen eller natten.
Det kan skyldes, at personer med aften- eller natarbejde producerer mindre melatonin, fordi de udsættes for lys om natten.
Lignende undersøgelser er i gang blandt mænd for at undersøge, om der også er en sammenhæng mellem aften- og natarbejde og prostatakræft.
Kræft og søvnbriller
Arbejder du om aftenen eller om natten og som følge deraf skal sove om dagen, kan det være en god idé at bruge søvnbriller 1-2 timer før du skal sove. Søvnbrillerne kan være med til at forlænge varigheden af melatoninproduktionen, så du får de normale og optimale 9-10 timer med melatonin i blodet pr. dag. Derudover er det afgørende, at du sover i et absolut mørklagt rum.
Forsøg
Et afgørende forsøg blev udført af de meget erfarne forskere; Dr. George Brainard, som er professor i neurologi og Dr. David Blask, som er forsker. De undersøgte blodprøver udtaget fra kvinder under tre forskellige forhold: om dagen, når melatonin ikke var til stede i blodet - i mørke om natten, når melatonin var til stede i blodet - og om natten, når kvinder har været udsat for flere timers lys. Der var ingen melatonin i blodet hos den sidste gruppe kvinder. I en anden fase af forsøget blev dette blod (uden melatonin) sprøjtet ind i menneskelige brysttumorer, der voksede i laboratorierotter. Dette resulterede i, at tumorerne voksede hurtigt. Indsprøjtning af blod med melatonin resulterede i, at tumorerne voksede langsomt, og nogle tumorer voksede slet ikke. Dr. Blask kommenterede, at blod indeholdende melatonin "bragte tumorer i dvale".
Forskning vedrørende kræft
Blåt lys i dagtimerne styrker den natlige døgnrytme og melatoninhæmning af menneskelig prostatacancervækst
Comp Med. 2015 Dec;65(6):473-85.Robert T Dauchy, Aaron E Hoffman, Melissa A Wren-Dail, John P Hanifin, Benjamin Warfield, George C Brainard, Shulin Xiang, Lin Yuan, Steven M Hill, Victoria P Belancio, Erin M Dauchy, Kara Smith, David E BlaskPMID: 26678364 / PMCID: PMC4681241
Vi testede hypotesen om, at udsættelse for blåt lys i dagtimerne styrker den natlige melatoninproduktion og øger hæmningen af metabolisme, signalaktivitet og vækst af prostatacancer xenografter. Disse data viser, at...
Blåt lys i dagtimerne styrker den natlige døgnrytme og melatoninhæmning af menneskelig prostatacancervækst
Vi testede hypotesen om, at udsættelse for blåt lys i dagtimerne styrker den natlige melatoninproduktion og øger hæmningen af metabolisme, signalaktivitet og vækst af prostatacancer xenografter. Disse data viser, at forstærkningen af natlige melatoninniveauer ved at udsætte nøgne rotter for blåt lys i dagtimerne signifikant reducerer human prostatacancer metaboliske, signalerende og proliferative aktiviteter.
Daytime Blue Light Enhances the Nighttime Circadian Melatonin Inhibition of Human Prostate Cancer Growth
Comp Med. 2015 Dec;65(6):473-85.
PMID: 26678364 / PMCID: PMC4681241
Melatonin: en brystkræft-hæmmer
Endocr Relat Cancer. 2015 Jun;22(3):R183-204. doi: 10.1530/ERC-15-0030. Epub 2015 Apr 15.Steven M Hill, Victoria P Belancio, Robert T Dauchy, Shulin Xiang, Samantha Brimer, Lulu Mao, Adam Hauch, Peter W Lundberg, Whitney Summers, Lin Yuan, Tripp Frasch, David E BlaskPMID: 25876649 / PMCID: PMC4457700 / DOI: 10.1530/ERC-15-0030
Undersøgelser har vist, at melatonin fremmer genomisk stabilitet ved at hæmme ekspressionen af LINE-1 retrotransposoner. Endelig har forskning i dyre- og menneskemodeller indikeret, at lys om natten forstyrrer produktionen af...
Melatonin: en brystkræft-hæmmer
Undersøgelser har vist, at melatonin fremmer genomisk stabilitet ved at hæmme ekspressionen af LINE-1 retrotransposoner. Endelig har forskning i dyre- og menneskemodeller indikeret, at lys om natten forstyrrer produktionen af melatonin og fremmer vækst, metabolisme og signalering af human brystkræft og driver brysttumorer til endokrin og kemoterapeutisk resistens. Disse data giver den stærkeste forståelse og støtte af de mekanismer, der understøtter den epidemiologiske demonstration af forhøjet brystkræftrisiko hos natholdsarbejdere.
Melatonin: an inhibitor of breast cancer
Endocr Relat Cancer. 2015 Jun;22(3):R183-204. doi: 10.1530/ERC-15-0030. Epub 2015 Apr 15.
PMID: 25876649 / PMCID: PMC4457700 / DOI: 10.1530/ERC-15-0030
Abstract
The present review discusses recent work on melatonin-mediated circadian regulation, the metabolic and molecular signaling mechanisms that are involved in human breast cancer growth, and the associated consequences of circadian disruption by exposure to light at night (LEN). The anti-cancer actions of the circadian melatonin signal in human breast cancer cell lines and xenografts heavily involve MT1 receptor-mediated mechanisms. In estrogen receptor alpha (ERα)-positive human breast cancer, melatonin suppresses ERα mRNA expression and ERα transcriptional activity via the MT1 receptor. Melatonin also regulates the transactivation of other members of the nuclear receptor superfamily, estrogen-metabolizing enzymes, and the expression of core clock and clock-related genes. Furthermore, melatonin also suppresses tumor aerobic metabolism (the Warburg effect) and, subsequently, cell-signaling pathways critical to cell proliferation, cell survival, metastasis, and drug resistance. Melatonin demonstrates both cytostatic and cytotoxic activity in breast cancer cells that appears to be cell type-specific. Melatonin also possesses anti-invasive/anti-metastatic actions that involve multiple pathways, including inhibition of p38 MAPK and repression of epithelial-mesenchymal transition (EMT). Studies have demonstrated that melatonin promotes genomic stability by inhibiting the expression of LINE-1 retrotransposons. Finally, research in animal and human models has indicated that LEN-induced disruption of the circadian nocturnal melatonin signal promotes the growth, metabolism, and signaling of human breast cancer and drives breast tumors to endocrine and chemotherapeutic resistance. These data provide the strongest understanding and support of the mechanisms that underpin the epidemiologic demonstration of elevated breast cancer risk in night-shift workers and other individuals who are increasingly exposed to LEN.
https://pubmed.ncbi.nlm.nih.gov/25876649/
The present review discusses recent work on melatonin-mediated circadian regulation, the metabolic and molecular signaling mechanisms that are involved in human breast cancer growth, and the associated consequences of circadian disruption by exposure to light at night (LEN). The anti-cancer actions of the circadian melatonin signal in human breast cancer cell lines and xenografts heavily involve MT1 receptor-mediated mechanisms. In estrogen receptor alpha (ERα)-positive human breast cancer, melatonin suppresses ERα mRNA expression and ERα transcriptional activity via the MT1 receptor. Melatonin also regulates the transactivation of other members of the nuclear receptor superfamily, estrogen-metabolizing enzymes, and the expression of core clock and clock-related genes. Furthermore, melatonin also suppresses tumor aerobic metabolism (the Warburg effect) and, subsequently, cell-signaling pathways critical to cell proliferation, cell survival, metastasis, and drug resistance. Melatonin demonstrates both cytostatic and cytotoxic activity in breast cancer cells that appears to be cell type-specific. Melatonin also possesses anti-invasive/anti-metastatic actions that involve multiple pathways, including inhibition of p38 MAPK and repression of epithelial-mesenchymal transition (EMT). Studies have demonstrated that melatonin promotes genomic stability by inhibiting the expression of LINE-1 retrotransposons. Finally, research in animal and human models has indicated that LEN-induced disruption of the circadian nocturnal melatonin signal promotes the growth, metabolism, and signaling of human breast cancer and drives breast tumors to endocrine and chemotherapeutic resistance. These data provide the strongest understanding and support of the mechanisms that underpin the epidemiologic demonstration of elevated breast cancer risk in night-shift workers and other individuals who are increasingly exposed to LEN.
https://pubmed.ncbi.nlm.nih.gov/25876649/
Brystkræft og forstyrrelse af døgnrytmen fra elektrisk belysning i den moderne verden
CA Cancer J Clin. 2014 May-Jun;64(3):207-18. doi: 10.3322/caac.21218. Epub 2013 Dec 24.Richard G Stevens, George C Brainard, David E Blask, Steven W Lockley, Mario E MottaPMID: 24604162 / PMCID: PMC4038658 / DOI: 10.3322/caac.21218
Brystkræft er den førende årsag til kræftdød blandt kvinder på verdensplan. Det er først for nylig blevet klart, at denne evolutionært nye og dermed unaturlige eksponering kan forstyrre menneskets døgnrytme,...
Brystkræft og forstyrrelse af døgnrytmen fra elektrisk belysning i den moderne verden
Brystkræft er den førende årsag til kræftdød blandt kvinder på verdensplan. Det er først for nylig blevet klart, at denne evolutionært nye og dermed unaturlige eksponering kan forstyrre menneskets døgnrytme, hvoraf tre fremtrædende træk er melatoninproduktion, søvn og døgnrytmen. Et innovativ forsøg har vist, at lys om natten markant øger væksten af humane brystkræft-xenotransplantater hos rotter. Hos mennesker fører teorien om, at udsættelse for lys om natten øger risikoen for brystkræft. Hvis elektrisk lys om natten forklarer en del af brystkræftbyrden, så er der praktiske indgreb, der kan implementeres, herunder mere selektiv brug af lys og vedtagelse af de seneste fremskridt inden for lysteknologi og anvendelse.
Breast cancer and circadian disruption from electric lighting in the modern world
CA Cancer J Clin. 2014 May-Jun;64(3):207-18. doi: 10.3322/caac.21218. Epub 2013 Dec 24.
PMID: 24604162 / PMCID: PMC4038658 / DOI: 10.3322/caac.21218
Abstract
Breast cancer is the leading cause of cancer death among women worldwide, and there is only a limited explanation of why. Risk is highest in the most industrialized countries but also is rising rapidly in the developing world. Known risk factors account for only a portion of the incidence in the high-risk populations, and there has been considerable speculation and many false leads on other possibly major determinants of risk, such as dietary fat. A hallmark of industrialization is the increasing use of electricity to light the night, both within the home and without. It has only recently become clear that this evolutionarily new and, thereby, unnatural exposure can disrupt human circadian rhythmicity, of which three salient features are melatonin production, sleep, and the circadian clock. A convergence of research in cells, rodents, and humans suggests that the health consequences of circadian disruption may be substantial. An innovative experimental model has shown that light at night markedly increases the growth of human breast cancer xenografts in rats. In humans, the theory that light exposure at night increases breast cancer risk leads to specific predictions that are being tested epidemiologically: evidence has accumulated on risk in shift workers, risk in blind women, and the impact of sleep duration on risk. If electric light at night does explain a portion of the breast cancer burden, then there are practical interventions that can be implemented, including more selective use of light and the adoption of recent advances in lighting technology and application.
https://pubmed.ncbi.nlm.nih.gov/24604162/
Breast cancer is the leading cause of cancer death among women worldwide, and there is only a limited explanation of why. Risk is highest in the most industrialized countries but also is rising rapidly in the developing world. Known risk factors account for only a portion of the incidence in the high-risk populations, and there has been considerable speculation and many false leads on other possibly major determinants of risk, such as dietary fat. A hallmark of industrialization is the increasing use of electricity to light the night, both within the home and without. It has only recently become clear that this evolutionarily new and, thereby, unnatural exposure can disrupt human circadian rhythmicity, of which three salient features are melatonin production, sleep, and the circadian clock. A convergence of research in cells, rodents, and humans suggests that the health consequences of circadian disruption may be substantial. An innovative experimental model has shown that light at night markedly increases the growth of human breast cancer xenografts in rats. In humans, the theory that light exposure at night increases breast cancer risk leads to specific predictions that are being tested epidemiologically: evidence has accumulated on risk in shift workers, risk in blind women, and the impact of sleep duration on risk. If electric light at night does explain a portion of the breast cancer burden, then there are practical interventions that can be implemented, including more selective use of light and the adoption of recent advances in lighting technology and application.
https://pubmed.ncbi.nlm.nih.gov/24604162/
Hypoteser for mekanismer, der forbinder skifteholdsarbejde og kræft
Med Hypotheses. 2011 Sep;77(3):430-6. doi: 10.1016/j.mehy.2011.06.002. Epub 2011 Jul 1.L Fritschi, D C Glass, J S Heyworth, K Aronson, J Girschik, T Boyle, A Grundy, T C ErrenPMID: 21723672 / DOI: 10.1016/j.mehy.2011.06.002
Man har på det seneste foretaget flere undersøgelser om, at en potentiel kræftrisiko kan være forbundet med natarbejde og skifteholdsarbejde. Vi foreslår yderligere fire mekanismer, der bør undersøges. Disse er:...
Hypoteser for mekanismer, der forbinder skifteholdsarbejde og kræft
Man har på det seneste foretaget flere undersøgelser om, at en potentiel kræftrisiko kan være forbundet med natarbejde og skifteholdsarbejde. Vi foreslår yderligere fire mekanismer, der bør undersøges. Disse er: faseskift, søvnforstyrrelser, livsstilsfaktorer (såsom kostvaner af dårlig kvalitet, mindre fysisk aktivitet og højere BMI) og mangel på D-vitamin. Det er nødvendigt at overveje disse fire mekanismer for, at udforme effektive forebyggende strategier til brug på arbejdspladserne.
Hypotheses for mechanisms linking shiftwork and cancer
Med Hypotheses. 2011 Sep;77(3):430-6. doi: 10.1016/j.mehy.2011.06.002. Epub 2011 Jul 1.
PMID: 21723672 / DOI: 10.1016/j.mehy.2011.06.002
Abstract
Shift work has been associated with various adverse health outcomes. In particular, there has been a recent flourish in investigating potential cancer risk associated with working night shifts and other shift schedules. Epidemiologic studies have revealed generally weak associations due to several methodological challenges such as lack of standard classifications of shift or night work. The field also has been hindered by a lack of clarity about the possible mechanisms by which shiftwork could have an effect on cancer risk. One possible mechanism is reduced production of melatonin caused by exposure to light at night. Although there is a growing body of evidence that provides some support for this mechanism, several other mechanisms also make sense from a biological point of view. Further, the relatively weak magnitude of the associations between light at night and melatonin level suggests that multiple factors may be operating along the pathway between shift work and adverse health consequences (including cancer risk). Here we propose four additional mechanisms that should be considered for a comprehensive investigation of these potential pathways. These are: phase shift; sleep disruption; lifestyle factors (such as poor quality diets, less physical activity and higher BMI); and lower vitamin D. Consideration of all these mechanisms is necessary in order to design effective preventative workplace strategies. In developed countries, approximately 20% of the population undertake shiftwork and, while we are unlikely to be able to eliminate shiftwork from current work practices, there are aspects of shiftwork that can be modified and there may be facets of individual susceptibility that we may be able to identify and target for prevention.
https://pubmed.ncbi.nlm.nih.gov/21723672/
Shift work has been associated with various adverse health outcomes. In particular, there has been a recent flourish in investigating potential cancer risk associated with working night shifts and other shift schedules. Epidemiologic studies have revealed generally weak associations due to several methodological challenges such as lack of standard classifications of shift or night work. The field also has been hindered by a lack of clarity about the possible mechanisms by which shiftwork could have an effect on cancer risk. One possible mechanism is reduced production of melatonin caused by exposure to light at night. Although there is a growing body of evidence that provides some support for this mechanism, several other mechanisms also make sense from a biological point of view. Further, the relatively weak magnitude of the associations between light at night and melatonin level suggests that multiple factors may be operating along the pathway between shift work and adverse health consequences (including cancer risk). Here we propose four additional mechanisms that should be considered for a comprehensive investigation of these potential pathways. These are: phase shift; sleep disruption; lifestyle factors (such as poor quality diets, less physical activity and higher BMI); and lower vitamin D. Consideration of all these mechanisms is necessary in order to design effective preventative workplace strategies. In developed countries, approximately 20% of the population undertake shiftwork and, while we are unlikely to be able to eliminate shiftwork from current work practices, there are aspects of shiftwork that can be modified and there may be facets of individual susceptibility that we may be able to identify and target for prevention.
https://pubmed.ncbi.nlm.nih.gov/21723672/
Total synsblindhed beskytter mod brystkræft
Cancer Causes Control. 2009 Nov;20(9):1753-6. doi: 10.1007/s10552-009-9405-0. Epub 2009 Aug 1.Erin E Flynn-Evans, Richard G Stevens, Homayoun Tabandeh, Eva S Schernhammer, Steven W LockleyPMID: 19649715 / DOI: 10.1007/s10552-009-9405-0
Selvom mængden af data er sparsom og baseret på små undersøgelser, så understøttes en lavere risiko for brystkræft hos blinde kvinder sammenlignet med seende kvinder. Mekanismer påvirket af okulær lysopfattelse,...
Total synsblindhed beskytter mod brystkræft
Selvom mængden af data er sparsom og baseret på små undersøgelser, så understøttes en lavere risiko for brystkræft hos blinde kvinder sammenlignet med seende kvinder. Mekanismer påvirket af okulær lysopfattelse, såsom melatonin eller døgnrytmesynkronisering, menes at tage højde for denne lavere risiko. For at evaluere, om blinde kvinder som ikke udsættes for lys, har en lavere forekomst af brystkræft sammenlignet med blinde kvinder som udsættes for lys, undersøgte vi 1.392 blinde kvinder, der bor i Nordamerika (66 tilfælde af brystkræft). Blinde kvinder som ikke udsættes for lys ser ud til at have en lavere risiko for brystkræft sammenlignet med blinde kvinder som udsættes for lys.
Total visual blindness is protective against breast cancer
Cancer Causes Control. 2009 Nov;20(9):1753-6. doi: 10.1007/s10552-009-9405-0. Epub 2009 Aug 1.
PMID: 19649715 / DOI: 10.1007/s10552-009-9405-0
Abstract
Objective: Observational data, though sparse and based on small studies with limited ability to control for known breast cancer risk factors, support a lower risk of breast cancer in blind women compared to sighted women. Mechanisms influenced by ocular light perception, such as melatonin or circadian synchronization, are thought to account for this lower risk.
Methods: To evaluate whether blind women with no perception of light (NPL) have a lower prevalence of breast cancer compared to blind women with light perception (LP), we surveyed a cohort of 1,392 blind women living in North America (66 breast cancer cases).
Results: In multivariate-logistic regression models controlling for breast cancer risk factors, women with NPL had a significantly lower prevalence of breast cancer than women with LP (odds ratio, 0.43; 95% confidence interval, 0.21-0.85). We observed little difference in these associations when restricting to postmenopausal women, non-shift workers or when excluding women diagnosed with breast cancer within 2 or 4 years of onset of blindness. Blind women with NPL appear to have a lower risk of breast cancer, compared to blind women with LP. More research is needed to elucidate the impact of LP on circadian coordination and melatonin production in the blind and how these factors may relate to breast cancer risk.
https://pubmed.ncbi.nlm.nih.gov/19649715/
Objective: Observational data, though sparse and based on small studies with limited ability to control for known breast cancer risk factors, support a lower risk of breast cancer in blind women compared to sighted women. Mechanisms influenced by ocular light perception, such as melatonin or circadian synchronization, are thought to account for this lower risk.
Methods: To evaluate whether blind women with no perception of light (NPL) have a lower prevalence of breast cancer compared to blind women with light perception (LP), we surveyed a cohort of 1,392 blind women living in North America (66 breast cancer cases).
Results: In multivariate-logistic regression models controlling for breast cancer risk factors, women with NPL had a significantly lower prevalence of breast cancer than women with LP (odds ratio, 0.43; 95% confidence interval, 0.21-0.85). We observed little difference in these associations when restricting to postmenopausal women, non-shift workers or when excluding women diagnosed with breast cancer within 2 or 4 years of onset of blindness. Blind women with NPL appear to have a lower risk of breast cancer, compared to blind women with LP. More research is needed to elucidate the impact of LP on circadian coordination and melatonin production in the blind and how these factors may relate to breast cancer risk.
https://pubmed.ncbi.nlm.nih.gov/19649715/
Melatonin, søvnforstyrrelse og risiko for kræft
Sleep Med Rev. 2009 Aug;13(4):257-64. doi: 10.1016/j.smrv.2008.07.007. Epub 2008 Dec 17.David E BlaskPMID: 19095474 / DOI: 10.1016/j.smrv.2008.07.007
Melatonin er involveret i regulering af døgnrytmen og gør det lettere at falde i søvn, hæmning af kræftudvikling og vækst samt forbedring af immunfunktionen. Nogle undersøgelser tyder på, at en...
Melatonin, søvnforstyrrelse og risiko for kræft
Melatonin er involveret i regulering af døgnrytmen og gør det lettere at falde i søvn, hæmning af kræftudvikling og vækst samt forbedring af immunfunktionen. Nogle undersøgelser tyder på, at en forkortet varighed af nattesøvn er forbundet med en højere risiko for udvikling af brystkræft. Den gensidige forstærkning af interagerende døgnrytmer af melatoninproduktion, søvn/vågen cyklus og immunfunktion kan indikere en ny rolle for uforstyrret søvn af høj kvalitet, og måske endnu vigtigere, uafbrudt mørke, som en tidligere ikke værdsat endogen mekanisme til kræftforebyggelse.
Melatonin, sleep disturbance and cancer risk
Sleep Med Rev. 2009 Aug;13(4):257-64. doi: 10.1016/j.smrv.2008.07.007. Epub 2008 Dec 17.
PMID: 19095474 / DOI: 10.1016/j.smrv.2008.07.007
Abstract
The pineal hormone melatonin is involved in the circadian regulation and facilitation of sleep, the inhibition of cancer development and growth, and the enhancement of immune function. Individuals, such as night shift workers, who are exposed to light at night on a regular basis experience biological rhythm (i.e., circadian) disruption including circadian phase shifts, nocturnal melatonin suppression, and sleep disturbances. Additionally, these individuals are not only immune suppressed, but they are also at an increased risk of developing a number of different types of cancer. There is a reciprocal interaction and regulation between sleep and the immune system quite independent of melatonin. Sleep disturbances can lead to immune suppression and a shift to the predominance in cancer-stimulatory cytokines. Some studies suggest that a shortened duration of nocturnal sleep is associated with a higher risk of breast cancer development. The relative individual contributions of sleep disturbance, circadian disruption due to light at night exposure, and related impairments of melatonin production and immune function to the initiation and promotion of cancer in high-risk individuals such as night shift workers are unknown. The mutual reinforcement of interacting circadian rhythms of melatonin production, the sleep/wake cycle and immune function may indicate a new role for undisturbed, high quality sleep, and perhaps even more importantly, uninterrupted darkness, as a previously unappreciated endogenous mechanism of cancer prevention.
https://pubmed.ncbi.nlm.nih.gov/19095474/
The pineal hormone melatonin is involved in the circadian regulation and facilitation of sleep, the inhibition of cancer development and growth, and the enhancement of immune function. Individuals, such as night shift workers, who are exposed to light at night on a regular basis experience biological rhythm (i.e., circadian) disruption including circadian phase shifts, nocturnal melatonin suppression, and sleep disturbances. Additionally, these individuals are not only immune suppressed, but they are also at an increased risk of developing a number of different types of cancer. There is a reciprocal interaction and regulation between sleep and the immune system quite independent of melatonin. Sleep disturbances can lead to immune suppression and a shift to the predominance in cancer-stimulatory cytokines. Some studies suggest that a shortened duration of nocturnal sleep is associated with a higher risk of breast cancer development. The relative individual contributions of sleep disturbance, circadian disruption due to light at night exposure, and related impairments of melatonin production and immune function to the initiation and promotion of cancer in high-risk individuals such as night shift workers are unknown. The mutual reinforcement of interacting circadian rhythms of melatonin production, the sleep/wake cycle and immune function may indicate a new role for undisturbed, high quality sleep, and perhaps even more importantly, uninterrupted darkness, as a previously unappreciated endogenous mechanism of cancer prevention.
https://pubmed.ncbi.nlm.nih.gov/19095474/
Lys om natten, døgnrytmeforstyrrelse, dæmpning af melatonin og kræftrisiko: en anmeldelse
Crit Rev Oncog. 2007 Dec;13(4):303-28. doi: 10.1615/critrevoncog.v13.i4.30.Russel J Reiter, Dun-Xian Tan, Ahmet Korkmaz, Thomas C Erren, Claus Piekarski, Hiroshi Tamura, Lucien C ManchesterPMID: 18540832 / DOI: 10.1615/critrevoncog.v13.i4.30
Lys om natten forstyrrer døgnrytmer og undertrykker produktionen af melatonin i pinealkirtlen. Undersøgelser på dyr har dokumenteret, at en potentiel negativ konsekvens ved forstyrrelse af hjernens indre ur og dæmpning...
Lys om natten, døgnrytmeforstyrrelse, dæmpning af melatonin og kræftrisiko: en anmeldelse
Lys om natten forstyrrer døgnrytmer og undertrykker produktionen af melatonin i pinealkirtlen. Undersøgelser på dyr har dokumenteret, at en potentiel negativ konsekvens ved forstyrrelse af hjernens indre ur og dæmpning af melatoninproduktion om natten er kræftfremkaldende og vækstfremmende. I epidemiologiske undersøgelser er hyppigheden af hver af de følgende kræftformer angiveligt blevet øget hos personer, der rutinemæssigt arbejder om natten, eller hvis døgnrytme er forstyrret af andre årsager (f.eks. på grund af jetlag): bryst, prostata, endometrium og kolorektal.
Light at night, chronodisruption, melatonin suppression, and cancer risk: a review
Crit Rev Oncog. 2007 Dec;13(4):303-28. doi: 10.1615/critrevoncog.v13.i4.30.
PMID: 18540832 / DOI: 10.1615/critrevoncog.v13.i4.30
Abstract
Light exposure during the night is becoming progressively more common throughout the world, particularly in areas where electricity is commonly used. Also, the availability of artificial light has allowed humans to work or recreate throughout the 24-hour day. Based on photographs taken of the Earth from outer space, it is also apparent that true darkness is disappearing. For years it was assumed that polluting the daily dark period with light was inconsequential in terms of animal/human physiology. That assumption, however, has proven incorrect. Light at night has two major physiological actions, i.e., it disrupts circadian rhythms and suppresses the production of melatonin by the pineal gland. Moreover, both these changes are light intensity and wavelength dependent. Both human epidemiological and experimental studies on animals have documented that a potential negative consequence of chronodisruption and nocturnal melatonin inhibition is cancer initiation and growth. In epidemiological studies, the frequency of each of the following cancers has been reportedly increased in individuals who routinely work at night or whose circadian rhythms are disrupted for other reasons (e.g., due to jet lag): breast, prostate, endometrial, and colorectal. Likewise, in experimental animals, cancer growth is exaggerated when the animals are repeatedly phase advanced (as occurs during easterly flights) or exposed to light at night. A variety of mechanisms have been examined to explain how the suppression of melatonin exaggerates cancer risk. Mechanistically, how chronodisruption (without a consideration of melatonin suppression) would enhance cancer frequency is less clear. In addition to cancer, there may be other diseases that result from the chronic suppression of melatonin by light at night.
https://pubmed.ncbi.nlm.nih.gov/18540832/
Light exposure during the night is becoming progressively more common throughout the world, particularly in areas where electricity is commonly used. Also, the availability of artificial light has allowed humans to work or recreate throughout the 24-hour day. Based on photographs taken of the Earth from outer space, it is also apparent that true darkness is disappearing. For years it was assumed that polluting the daily dark period with light was inconsequential in terms of animal/human physiology. That assumption, however, has proven incorrect. Light at night has two major physiological actions, i.e., it disrupts circadian rhythms and suppresses the production of melatonin by the pineal gland. Moreover, both these changes are light intensity and wavelength dependent. Both human epidemiological and experimental studies on animals have documented that a potential negative consequence of chronodisruption and nocturnal melatonin inhibition is cancer initiation and growth. In epidemiological studies, the frequency of each of the following cancers has been reportedly increased in individuals who routinely work at night or whose circadian rhythms are disrupted for other reasons (e.g., due to jet lag): breast, prostate, endometrial, and colorectal. Likewise, in experimental animals, cancer growth is exaggerated when the animals are repeatedly phase advanced (as occurs during easterly flights) or exposed to light at night. A variety of mechanisms have been examined to explain how the suppression of melatonin exaggerates cancer risk. Mechanistically, how chronodisruption (without a consideration of melatonin suppression) would enhance cancer frequency is less clear. In addition to cancer, there may be other diseases that result from the chronic suppression of melatonin by light at night.
https://pubmed.ncbi.nlm.nih.gov/18540832/
Melatonin-udtømt blod fra præmenopausale kvinder udsat for lys om natten, stimulerer væksten af humane brystkræft xenotransplantater hos nøgne rotter
Cancer Res. 2005 Dec 1;65(23):11174-84. doi: 10.1158/0008-5472.CAN-05-1945.David E Blask, George C Brainard, Robert T Dauchy, John P Hanifin, Leslie K Davidson, Jean A Krause, Leonard A Sauer, Moises A Rivera-Bermudez, Margarita L Dubocovich, Samar A Jasser, Darin T Lynch, Mark D Rollag, Frederick ZalatanPMID: 16322268 / DOI: 10.1158/0008-5472.CAN-05-1945
Det er blevet postuleret at den øgede risiko for brystkræft hos kvindelige skifteholdsarbejdere skyldes dæmpning af melatoninproduktion ved udsættelse for lys om natten. Disse resultater er de første, der viser,...
Melatonin-udtømt blod fra præmenopausale kvinder udsat for lys om natten, stimulerer væksten af humane brystkræft xenotransplantater hos nøgne rotter
Det er blevet postuleret at den øgede risiko for brystkræft hos kvindelige skifteholdsarbejdere skyldes dæmpning af melatoninproduktion ved udsættelse for lys om natten. Disse resultater er de første, der viser, at tumorvækstresponsen ved udsættelse for lys i mørke er intensitetsafhængig, og at det menneskelige natlige, døgnrytme melatonin-signalstof ikke kun hæmmer human brystkræftvækst, men at denne effekt fjernes ved kortvarig øjeneksponering for stærkt, hvidt lys om natten.
Melatonin-depleted blood from premenopausal women exposed to light at night stimulates growth of human breast cancer xenografts in nude rats
Cancer Res. 2005 Dec 1;65(23):11174-84. doi: 10.1158/0008-5472.CAN-05-1945.
PMID: 16322268 / DOI: 10.1158/0008-5472.CAN-05-1945
Abstract
The increased breast cancer risk in female night shift workers has been postulated to result from the suppression of pineal melatonin production by exposure to light at night. Exposure of rats bearing rat hepatomas or human breast cancer xenografts to increasing intensities of white fluorescent light during each 12-hour dark phase (0-345 microW/cm2) resulted in a dose-dependent suppression of nocturnal melatonin blood levels and a stimulation of tumor growth and linoleic acid uptake/metabolism to the mitogenic molecule 13-hydroxyoctadecadienoic acid. Venous blood samples were collected from healthy, premenopausal female volunteers during either the daytime, nighttime, or nighttime following 90 minutes of ocular bright, white fluorescent light exposure at 580 microW/cm2 (i.e., 2,800 lx). Compared with tumors perfused with daytime-collected melatonin-deficient blood, human breast cancer xenografts and rat hepatomas perfused in situ, with nocturnal, physiologically melatonin-rich blood collected during the night, exhibited markedly suppressed proliferative activity and linoleic acid uptake/metabolism. Tumors perfused with melatonin-deficient blood collected following ocular exposure to light at night exhibited the daytime pattern of high tumor proliferative activity. These results are the first to show that the tumor growth response to exposure to light during darkness is intensity dependent and that the human nocturnal, circadian melatonin signal not only inhibits human breast cancer growth but that this effect is extinguished by short-term ocular exposure to bright, white light at night. These mechanistic studies are the first to provide a rational biological explanation for the increased breast cancer risk in female night shift workers.
https://pubmed.ncbi.nlm.nih.gov/16322268/
The increased breast cancer risk in female night shift workers has been postulated to result from the suppression of pineal melatonin production by exposure to light at night. Exposure of rats bearing rat hepatomas or human breast cancer xenografts to increasing intensities of white fluorescent light during each 12-hour dark phase (0-345 microW/cm2) resulted in a dose-dependent suppression of nocturnal melatonin blood levels and a stimulation of tumor growth and linoleic acid uptake/metabolism to the mitogenic molecule 13-hydroxyoctadecadienoic acid. Venous blood samples were collected from healthy, premenopausal female volunteers during either the daytime, nighttime, or nighttime following 90 minutes of ocular bright, white fluorescent light exposure at 580 microW/cm2 (i.e., 2,800 lx). Compared with tumors perfused with daytime-collected melatonin-deficient blood, human breast cancer xenografts and rat hepatomas perfused in situ, with nocturnal, physiologically melatonin-rich blood collected during the night, exhibited markedly suppressed proliferative activity and linoleic acid uptake/metabolism. Tumors perfused with melatonin-deficient blood collected following ocular exposure to light at night exhibited the daytime pattern of high tumor proliferative activity. These results are the first to show that the tumor growth response to exposure to light during darkness is intensity dependent and that the human nocturnal, circadian melatonin signal not only inhibits human breast cancer growth but that this effect is extinguished by short-term ocular exposure to bright, white light at night. These mechanistic studies are the first to provide a rational biological explanation for the increased breast cancer risk in female night shift workers.
https://pubmed.ncbi.nlm.nih.gov/16322268/
Natarbejde og risiko for brystkræft: en systematisk gennemgang og metaanalyse
Eur J Cancer. 2005 Sep;41(13):2023-32. doi: 10.1016/j.ejca.2005.05.010.Sarah P Megdal, Candyce H Kroenke, Francine Laden, Eero Pukkala, Eva S SchernhammerPMID: 16084719 / DOI: 10.1016/j.ejca.2005.05.010
Sammenhængen mellem erhverv, der involverer natarbejde (et surrogat til eksponering for lys om natten med efterfølgende dæmpning af melatoninproduktion) og risiko for brystkræft er usikker. Vi gennemførte derfor en systematisk...
Natarbejde og risiko for brystkræft: en systematisk gennemgang og metaanalyse
Sammenhængen mellem erhverv, der involverer natarbejde (et surrogat til eksponering for lys om natten med efterfølgende dæmpning af melatoninproduktion) og risiko for brystkræft er usikker. Vi gennemførte derfor en systematisk gennemgang og meta-analyse af observationsstudier for at vurdere effekterne af natarbejde ved risiko for brystkræft. Undersøgelser af natteholdsarbejde og risiko for brystkræft viser samlet set en øget risiko for brystkræft blandt kvinder.
Night work and breast cancer risk: a systematic review and meta-analysis
Eur J Cancer. 2005 Sep;41(13):2023-32. doi: 10.1016/j.ejca.2005.05.010.
PMID: 16084719 / DOI: 10.1016/j.ejca.2005.05.010
Abstract
The association between occupations that involve night shift work (a surrogate for exposure to light at night with subsequent melatonin suppression) and breast cancer risk is uncertain. We therefore conducted a systematic review and meta-analysis of observational studies to assess the effects of night work on breast cancer risk. Data sources were MEDLINE from January 1960 to January 2005, experts in the field, bibliographies, and abstracts. Search terms included night work terms, flight personnel terms, cancer terms, and risk terms. Independent data extraction by two authors using standardised forms was performed. The method of DerSimonian and Laird was used to derive combined estimates and Egger's; and Begg and Mazumdar's tests for publication bias were conducted. Based on 13 studies, including seven studies of airline cabin crew and six studies of other night shift workers, the aggregate estimate for all studies combined was 1.48 (95% CI, 1.36-1.61), with a similar significant elevation of breast cancer risk among female airline cabin crew (standardised incidence ratio (SIR), 1.44; 95% CI, 1.26-1.65), and female night workers (relative risk (RR), 1.51; 95% CI, 1.36-1.68) separately. We found some evidence suggesting confounding due to incomplete adjustment for breast cancer risk factors, with smaller effects in the studies that more completely adjusted for reproductive history and other confounding factors. Egger's and Begg and Mazumdar's tests for publication bias showed no significant asymmetry (P>0.05). Studies on night shift work and breast cancer risk collectively show an increased breast cancer risk among women. Publication bias is unlikely to have influenced the results.
https://pubmed.ncbi.nlm.nih.gov/16084719/
The association between occupations that involve night shift work (a surrogate for exposure to light at night with subsequent melatonin suppression) and breast cancer risk is uncertain. We therefore conducted a systematic review and meta-analysis of observational studies to assess the effects of night work on breast cancer risk. Data sources were MEDLINE from January 1960 to January 2005, experts in the field, bibliographies, and abstracts. Search terms included night work terms, flight personnel terms, cancer terms, and risk terms. Independent data extraction by two authors using standardised forms was performed. The method of DerSimonian and Laird was used to derive combined estimates and Egger's; and Begg and Mazumdar's tests for publication bias were conducted. Based on 13 studies, including seven studies of airline cabin crew and six studies of other night shift workers, the aggregate estimate for all studies combined was 1.48 (95% CI, 1.36-1.61), with a similar significant elevation of breast cancer risk among female airline cabin crew (standardised incidence ratio (SIR), 1.44; 95% CI, 1.26-1.65), and female night workers (relative risk (RR), 1.51; 95% CI, 1.36-1.68) separately. We found some evidence suggesting confounding due to incomplete adjustment for breast cancer risk factors, with smaller effects in the studies that more completely adjusted for reproductive history and other confounding factors. Egger's and Begg and Mazumdar's tests for publication bias showed no significant asymmetry (P>0.05). Studies on night shift work and breast cancer risk collectively show an increased breast cancer risk among women. Publication bias is unlikely to have influenced the results.
https://pubmed.ncbi.nlm.nih.gov/16084719/
Melatoninniveauer i urinen og risiko for brystkræft
J Natl Cancer Inst. 2005 Jul 20;97(14):1084-7. doi: 10.1093/jnci/dji190.Eva S Schernhammer, Susan E HankinsonPMID: 16030307 / DOI: 10.1093/jnci/dji190
Eksponering for lys om natten dæmper produktionen af melatonin, og natholdsarbejde (et surrogat for sådan eksponering) har været forbundet med en øget risiko for brystkræft. I et prospektivt case-kontrolstudie målte...
Melatoninniveauer i urinen og risiko for brystkræft
Eksponering for lys om natten dæmper produktionen af melatonin, og natholdsarbejde (et surrogat for sådan eksponering) har været forbundet med en øget risiko for brystkræft. I et prospektivt case-kontrolstudie målte vi koncentrationen af den vigtigste melatoninmetabolit, 6-sulphatoxymelatonin (aMT6s), i den første morgenurin fra 147 kvinder med invasiv brystkræft og 291 matchende kontrol emner. Disse prospektive data understøtter hypotesen om, at højere melatoninniveauer, målt i første morgenurin, er forbundet med en lavere risiko for brystkræft.
Urinary melatonin levels and breast cancer risk
J Natl Cancer Inst. 2005 Jul 20;97(14):1084-7. doi: 10.1093/jnci/dji190.
PMID: 16030307 / DOI: 10.1093/jnci/dji190
Abstract
Exposure to light at night suppresses melatonin production, and night-shift work (a surrogate for such exposure) has been associated with an increased risk of breast cancer. However, the association between circulating melatonin levels and breast cancer risk is unclear. In a prospective case-control study nested within the Nurses' Health Study II cohort, we measured the concentration of the major melatonin metabolite, 6-sulphatoxymelatonin (aMT6s), in the first morning urine of 147 women with invasive breast cancer and 291 matched control subjects. In logistic regression models, the relative risk (reported as the odds ratio [OR]) of invasive breast cancer for women in the highest quartile of urinary aMT6s compared with those in the lowest was 0.59 (95% confidence interval [CI] = 0.36 to 0.97). This association was essentially unchanged after adjustment for breast cancer risk factors or plasma sex hormone levels but was slightly weakened when the analysis included 43 case patients with in situ breast cancer and their 85 matched control subjects (OR = 0.70, 95% CI = 0.47 to 1.06). The exclusion of women who had a history of night-shift work left our findings largely unchanged. These prospective data support the hypothesis that higher melatonin levels, as measured in first morning urine, are associated with a lower risk of breast cancer.
https://pubmed.ncbi.nlm.nih.gov/16030307/
Exposure to light at night suppresses melatonin production, and night-shift work (a surrogate for such exposure) has been associated with an increased risk of breast cancer. However, the association between circulating melatonin levels and breast cancer risk is unclear. In a prospective case-control study nested within the Nurses' Health Study II cohort, we measured the concentration of the major melatonin metabolite, 6-sulphatoxymelatonin (aMT6s), in the first morning urine of 147 women with invasive breast cancer and 291 matched control subjects. In logistic regression models, the relative risk (reported as the odds ratio [OR]) of invasive breast cancer for women in the highest quartile of urinary aMT6s compared with those in the lowest was 0.59 (95% confidence interval [CI] = 0.36 to 0.97). This association was essentially unchanged after adjustment for breast cancer risk factors or plasma sex hormone levels but was slightly weakened when the analysis included 43 case patients with in situ breast cancer and their 85 matched control subjects (OR = 0.70, 95% CI = 0.47 to 1.06). The exclusion of women who had a history of night-shift work left our findings largely unchanged. These prospective data support the hypothesis that higher melatonin levels, as measured in first morning urine, are associated with a lower risk of breast cancer.
https://pubmed.ncbi.nlm.nih.gov/16030307/
Natarbejde, lys om natten og risiko for brystkræft
JNCI: Journal of the National Cancer Institute, Volume 93, Issue 20, 17 October 2001, Pages 1557-1562Scott Davis, Dana K. Mirick, Richard G. StevensPDMI:0
Udsættelse for lys om natten kan øge risikoen for brystkræft ved at dæmpe den normale natlige produktion af melatonin i pinealkirtlen, hvilket igen kan øge frigivelsen af østrogen fra æggestokkene....
Natarbejde, lys om natten og risiko for brystkræft
Udsættelse for lys om natten kan øge risikoen for brystkræft ved at dæmpe den normale natlige produktion af melatonin i pinealkirtlen, hvilket igen kan øge frigivelsen af østrogen fra æggestokkene. Denne undersøgelse undersøgte, om en sådan eksponering er forbundet med en øget risiko for brystkræft hos kvinder. Skifteholdsarbejde fra sent om aftenen til morgen var forbundet med øget risiko for brystkræft, med en tendens til øget risiko. Konklusion: Resultaterne af denne undersøgelse giver bevis for, at indikatorer for eksponering for lys om natten kan være forbundet med risiko for at udvikle brystkræft.
Night Shift Work, Light at Night, and Risk of Breast Cancer
JNCI: Journal of the National Cancer Institute, Volume 93, Issue 20, 17 October 2001, Pages 1557-1562
PDMI:0
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 disgnosed 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 group. 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.
Result: 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.
https://pubmed.ncbi.nlm.nih.gov/11604479/
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 disgnosed 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 group. 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.
Result: 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.
https://pubmed.ncbi.nlm.nih.gov/11604479/