Night-shift work and risk of colorectal cancer in the nurses' health study

Melatonin and ulcerative colitis: evidence, biological mechanisms, and future research

Ulcerative colitis (UC) is an inflammatory bowel disease that afflicts up to 1 million people in the US. Current treatments for UC are mostly nonspecific, not always effective, and often accompanied by serious side effects. Therefore, there is considerable interest in finding alternative and more tolerable treatments for this disease. Physiologic data suggest that melatonin is an important regulator of both inflammation and motility in the gastrointestinal tract, and data from in vitro studies, animal experiments, and limited studies in humans suggest that supplemental melatonin may have an ameliorative effect on colitis. In this review we summarize the evidence regarding melatonin as a possible therapeutic agent in UC and discuss possible biological mechanisms and directions for future research.

Transcriptional profiling of mRNA expression in the mouse distal colon

BACKGROUND & AIMS

Intestinal epithelial cells and the myenteric plexus of the mouse gastrointestinal tract contain a circadian clock-based intrinsic time-keeping system. Because disruption of the biological clock has been associated with increased susceptibility to colon cancer and gastrointestinal symptoms, we aimed to identify rhythmically expressed genes in the mouse distal colon.

METHODS

Microarray analysis was used to identify genes that were rhythmically expressed over a 24-hour light/dark cycle. The transcripts were then classified according to expression pattern, function, and association with physiologic and pathophysiologic processes of the colon.

RESULTS

A circadian gene expression pattern was detected in approximately 3.7% of distal colonic genes. A large percentage of these genes were involved in cell signaling, differentiation, and proliferation and cell death. Of all the rhythmically expressed genes in the mouse colon, approximately 7% (64/906) have been associated with colorectal cancer formation (eg, B-cell leukemia/lymphoma-2 [Bcl2]) and 1.8% (18/906) with various colonic functions such as motility and secretion (eg, vasoactive intestinal polypeptide, cystic fibrosis transmembrane conductance regulator).

CONCLUSIONS

A subset of genes in the murine colon follows a rhythmic expression pattern. These findings may have significant implications for colonic physiology and pathophysiology.

Selectively filtering short wavelengths attenuates the disruptive effects of nocturnal light on endocrine and molecular circadian phase markers in rats

Various physiological processes exhibit a circadian rhythm synchronized to the geophysical light/dark cycle. Our study using a rat model demonstrated that exposure to light at night suppressed the expected nocturnal rise in melatonin, increased plasma corticosterone, and disrupted core clock gene expression in the hypothalamus and the adrenal gland. These effects were prevented by filtration of a 10-nm bandwidth of light between 470 and 480 nm, whereas filtration of light between 452 and 462 nm prevented the rise of corticosterone without restoring normal melatonin secretion or hypothalamic clock gene expression. This is the first demonstration of a wavelength dependency of glucocorticoid secretion and clock gene expression. Our results in an animal model suggest that filtering a narrow bandwidth of light from nocturnal lighting may efficiently attenuate overall disruption of circadian endocrine rhythms and clock gene expression in the hypothalamus and adrenal gland. Because a narrow bandwidth of light is filtered, the color distribution of the illumination source is not altered, and this may be of practical importance for potential future studies in shift workers.

Visualizing jet lag in the mouse suprachiasmatic nucleus and peripheral circadian timing system

Circadian rhythms regulate most physiological processes. Adjustments to circadian time, called phase shifts, are necessary following international travel and on a more frequent basis for individuals who work non-traditional schedules such as rotating shifts. As the disruption that results from frequent phase shifts is deleterious to both animals and humans, we sought to better understand the kinetics of resynchronization of the mouse circadian system to one of the most disruptive phase shifts, a 6-h phase advance. Mice bearing a luciferase reporter gene for mPer2 were subjected to a 6-h advance of the light cycle and molecular rhythms in suprachiasmatic nuclei (SCN), thymus, spleen, lung and esophagus were measured periodically for 2 weeks following the shift. For the SCN, the master pacemaker in the brain, we employed high-resolution imaging of the brain slice to describe the resynchronization of rhythms in single SCN neurons during adjustment to the new light cycle. We observed significant differences in shifting kinetics among mice, among organs such as the spleen and lung, and importantly among neurons in the SCN. The phase distribution among all Period2-expressing SCN neurons widened on the day following a shift of the light cycle, which was partially due to cells in the ventral SCN exhibiting a larger initial phase shift than cells in the dorsal SCN. There was no clear delineation of ventral and dorsal regions, however, as the SCN appear to have a population of fast-shifting cells whose anatomical distribution is organized in a ventral-dorsal gradient. Full resynchronization of the SCN and peripheral timing system, as measured by a circadian reporter gene, did not occur until after 8 days in the advanced light cycle.

Melatonin suppresses AOM/DSS-induced large bowel oncogenesis in rats

The inhibitory effects of exogenous melatonin (MEL) on colon oncogenesis were investigated using an azoxymethane (AOM)/dextran sodium sulfate (DSS) rat model. Male F344 rats initiated with a single intraperitoneal injection of AOM (20mg/kg bw) were promoted by 1% (w/v) DSS in drinking water for 7 days. They were then given 0.4, 2 or 10ppm MEL in drinking water for 17 weeks. At week 20, the development of colonic adenocarcinoma was significantly inhibited by the administration with MEL dose-dependently. MEL exposure modulated the mitotic and apoptotic indices in the colonic adenocarcinomas that developed and lowered the immunohistochemical expression of nuclear factor kappa B, tumor necrosis factor alpha, interleukin-1beta and STAT3 in the epithelial malignancies. These results may indicate the beneficial effects of MEL on colitis-related colon carcinogenesis and a potential application for inhibiting colorectal cancer development in the inflamed colon.

Critical role of glutathione in melatonin enhancement of tumor necrosis factor and ionizing radiation-induced apoptosis in prostate cancer cells in vitro

The role of antioxidants in reducing cancer initiation and progression has been highlighted in recent years. Not only antioxidants limit cancer cell growth but also, in some situations, they promote the effectiveness of conventional treatments. Melatonin, an endogenously synthesized antioxidant, reduces cell growth of several tumor types both in vivo and in vitro. Additionally, the indole limits the collateral damage induced by many chemotherapeutic agents. By using a cellular model of human prostate cancer, we studied the ability of melatonin to enhance apoptosis induced by tumor necrosis factor or gamma radiation. It has been reported that melatonin reduces prostate cancer cell growth and, more recently, it promotes cell differentiation. In this work, we also show that melatonin elevates p21 protein levels and increases antioxidant capacity of prostate cancer cells. In addition, melatonin significantly enhances hrTNFalpha induced cell death by decreasing NFkappaB activation. Bcl-2 and survivin down-regulation appears to be associated to apoptosis stimulation under NFkappaB inhibition. On the contrary, melatonin does not promote irradiation-induced cell death due to an increment in intracellular glutathione content. In conclusion, prevention of NFkappaB activation by melatonin enhances the effectiveness of cytokine treatment in prostate cancer cells but it is not sufficient to enhance cell death triggered by other therapies which generate free radicals. A crucial role of glutathione in survival mechanisms of prostate cancer cells should be carefully considered.

Therapeutic Actions of Melatonin in Cancer: Possible Mechanisms

Melatonin is a phylogenetically well-preserved molecule with diverse physiological functions. In addition to its well-known regulatory control of the sleep/wake cycle, as well as circadian rhythms generally, melatonin is involved in immunomodulation, hematopoiesis, and antioxidative processes. Recent human and animal studies have now shown that melatonin also has important oncostatic properties. Both at physiological and pharmacological doses melatonin exerts growth inhibitory effects on breast cancer cell lines. In hepatomas, through its activation of MT 1 and MT2 receptors, melatonin inhibits linoleic acid uptake, thereby preventing the formation of the mitogenic metabolite 1,3-hydroxyoctadecadienoic acid. In animal model studies, melatonin has been shown to have preventative action against nitrosodiethylamine (NDEA)-induced liver cancer. Melatonin also inhibits the growth of prostate tumors via activation of MT1 receptors thereby inducing translocation of the androgen receptor to the cytoplasm and inhibition of the effect of endogenous androgens. There is abundant evidence indicating that melatonin is involved in preventing tumor initiation, promotion, and progression. The anticarcinogenic effect of melatonin on neoplastic cells relies on its antioxidant, immunostimulating, and apoptotic properties. Melatonin's oncostatic actions include the direct augmentation of natural killer (NK) cell activity, which increases immunosurveillance, as well as the stimulation of cytokine production, for example, of interleukin (IL)-2, IL-6, IL-12, and interferon (IFN)-γ. In addition to its direct oncostatic action, melatonin protects hematopoietic precursors from the toxic effect of anticancer chemotherapeutic drugs. Melatonin secretion is impaired in patients suffering from breast cancer, endometrial cancer, or colorectal cancer. The increased incidence of breast cancer and colorectal cancer seen in nurses and other night shift workers suggests a possible link between diminished secretion of melatonin and increased exposure to light during nighttime. The physiological surge of melatonin at night is thus considered a “natural restraint” on tumor initiation, promotion, and progression.

The relationship between lifestyle, working environment, socio-demographic factors and expulsion from the labour market due to disability pension among nurses

BACKGROUND

Denmark is facing a shortage of nurses and this trend is anticipated to worsen within the next decades. The major reason for this shortage is that only very few nurses remain employed until the general retirement age. Every year several nurses are expelled from the labour market prematurely which causes a problem not only for the disabled nurses but also because it can affect the morale and productivity among the remaining personnel while new staff members are hired and trained.

AIM

The aim of the study was to analyse the relationship between lifestyle, working environment, socio-demographic factors and disability pension (DP) among nurses.

METHODS

The study was based on 12,028 nurses above the age of 44 who in 1993 completed a questionnaire. The survey information was combined with longitudinal data from a register compiled by Statistics Denmark. The follow-up period was from 1993 to 2002.

RESULTS

Nurses with relatively low gross incomes were more likely to become disability pensioners compared to nurses with high incomes (hazard ratio, HR 1.33 and HR 2.17). Also, nurses who were singles had a higher probability of entering DP (HR 1.63). Nurses who worked fixed evening or night shifts had higher risks of DP than nurses who worked daytime exclusively (HR 1.51 and HR 1.45). Smoking, obesity and having a sedentary lifestyle were also risk indicators for DP (HR 1.42, HR 1.63 and HR 1.50). Furthermore, low influence and high physical demands at work increased the probability of entering DP (HR 1.39 and HR 1.22).

CONCLUSION

DP among nurses is influenced by a number of factors. Nurses who have poor working environments and/or unhealthy lifestyles have higher risks of becoming disability pensioners. Also, nurses who are singles and/or have low gross incomes have higher probability of entering DP.

Morbidity of Israeli nurses in comparison to their female siblings: a retrospective cohort study

This study of nurses' risk of selected chronic diseases in the context of potential biological exposure compares the health status of nurses to that of their female siblings. Self-report questionnaires distributed to each participating nurse were administered to an historical cohort of 491 female nurses aged > or =50 years. Questionnaires covered work and health history of the nurses and the control group of 232 of their age-matched female siblings. We developed a semiquantitative exposure matrix based on workplaces to describe biological exposure. Risk for coronary heart diseases, high blood pressure, dislipidemia, and thyroid and liver disease was significantly higher among the nurses compared to the controls. Total cancer and diabetes risks were similar for both groups. Cumulative biological exposure was associated with liver disease. Employment as a nurse may pose a risk for cardiovascular, thyroid and liver diseases. The specific determinants of this increased risk warrant further investigation.

Health disparities among America's health care providers: evidence from the Integrated Health Interview Series, 1982 to 2004

OBJECTIVE

To examine whether health status and obesity prevalence differ by race or ethnicity and health care workforce category.

METHODS

Data representing US health care workers aged 20 to 64 between 1982 and 2004 were retrieved from the Integrated Health Interview Series. Trends, as well as disparities, in health status and obesity are examined by workforce category using logistic regression.

RESULTS

Self-reported health status of health care workers has declined over time and the prevalence of obesity is rising. Moreover, there is a clear social gradient across workforce categories, which is widening over time. Within workforce categories, there are significant racial disparities in health status and prevalence of obesity.

CONCLUSIONS

Health of health care workers needs to be taken into account when setting policies intended to increase access to health care and create a healthy diverse workforce.

Altered Stra13 and Dec2 circadian gene expression in hypoxic cells

The circadian system regulates rhythmically most of the mammalian physiology in synchrony with the environmental light/dark cycle. Alteration of circadian clock gene expression has been associated with tumour progression but the molecular links between the two mechanisms remain poorly defined. Here we show that Stra13 and Dec2, two circadian transcriptional regulators which play a crucial role in cell proliferation and apoptosis are overexpressed and no longer rhythmic in serum shocked fibroblasts treated with CoCl(2,) a substitute of hypoxia. This effect is associated with a loss of circadian expression of the clock genes Rev-erbalpha and Bmal1, and the clock-controlled gene Dbp. Consistently, cotransfection assays demonstrate that STRA13 and DEC2 both antagonize CLOCK:BMAL1 dependent transactivation of the Rev-erbalpha and Dbp promoters. Using a transplantable osteosarcoma tumour model, we show that hypoxia is associated with altered circadian expression of Stra13, Dec2, Rev-erbalpha, Bmal1 and Dbp in vivo. These observations collectively support the notion that overexpression of Stra13 and Dec2 links hypoxia signalling to altered circadian clock gene expression.

Assessment of DNA damage in Japanese nurses handling antineoplastic drugs by the comet assay

To clarify genotoxic effects of occupational exposure to antineoplastic drugs in Japan, we examined DNA damage, assessed by the comet assay, in 121 female nurses and 46 female clerks working at three hospitals in the northeast of Japan. The comet assay is considered to be a sensitive and rapid method for DNA strand break detection in individual cells, and tail length and tail moment are used as the comet parameters. Concerning the basal characteristics, the 46 control subjects had higher rates of smoking and coffee-drinking habits and lower hemoglobin than the 121 nurses (p<0.05). The log-transformed tail length in the nurses was significantly longer than that in the control subjects after adjusting for possible covariates such as age and smoking habit (p<0.05). Also, the log-transformed tail length was significantly longer, in the 57 nurses who had handled antineoplastic drugs in the last six months, than that in the 46 control subjects (p<0.05); but, no significant difference in tail length or tail moment was seen between the two nurse groups with and without experience of handling hazardous drugs (p>0.05). These results suggest that Japanese nurses who have worked at hospitals using antineoplastic drugs may have a potential risk of DNA damage. To minimize this risk in Japan, use of biological safety cabinet and appropriate protective equipment, in addition to staff education and training, should be implemented in the healthcare environment.

Mortality and cancer incidence in a cohort of registered nurses from British Columbia, Canada

BACKGROUND

A retrospective cohort study of provincial registered nurses (RNs) from British Columbia, Canada was undertaken to determine risks of mortality and cancer incidence; in particular for breast cancer and leukemia.

METHODS

Cohort records of RNs from 1974 to 2000 were linked to Canadian death and cancer registries. Analyses included standardized mortality (SMR) and incidence ratios (SIR) as well as relative risks for internal comparisons.

RESULTS

There were 58,125 RNs in the cohort (96.7% females). The SMR for all causes of mortality for female RNs was low, at 0.61 (95% CI, 0.58-0.64). The only elevated SIR for female RNs was for malignant melanoma (1.27; 95% CI, 1.10-1.46). Ever working in a hospital, medical surgical specialties or maternal/pediatrics showed some elevated cancer risks.

CONCLUSIONS

Low SMRs for the female RN cohort suggest healthful lifestyles and a healthy worker effect. Length of employment as a nurse, in hospitals and in specific fields was associated with some increased risks of cancer.

Night shift work and the risk of endometrial cancer

Melatonin has several oncostatic properties, including possible anti-estrogenic and anti-aromatase activity, and seems to be linked with fat metabolism. Night workers have lower levels of melatonin, which may predispose them to develop cancer. Endometrial cancer risk is influenced significantly by hormonal and metabolic factors; therefore, we hypothesize that night workers may have an increased risk of endometrial cancer. Of the 121,701 women enrolled in a prospective cohort study, 53,487 women provided data on rotating night shift work in 1988 and were followed through on June 1, 2004. A total of 515 women developed medical record-confirmed invasive endometrial cancer. We used Cox regression models to calculate multivariate relative risks (MVRRs), controlling for endometrial cancer risk factors. Women who worked 20+ years of rotating night shifts had a significantly increased risk of endometrial cancer [MVRR, 1.47; 95% confidence interval (95% CI), 1.03-1.14]. In stratified analyses, obese women working rotating night shifts doubled their baseline risk of endometrial cancer (MVRR, 2.09; 95% CI, 1.24-3.52) compared with obese women who did no night work, whereas a nonsignificant increase was seen among non-obese women (MVRR, 1.07; 95% CI, 0.60-1.92). Women working rotating night shifts for a long duration have a significantly increased risk of endometrial cancer, particularly if they are obese. We speculate that this increased risk is attributable to the effects of melatonin on hormonal and metabolic factors. Our results add to growing literature that suggests women who work at night may benefit from cancer prevention strategies.

Are circadian rhythms the code of hypothalamic-immune communication? Insights from natural killer cells

Circadian rhythms in physiology and behavior are ultimately regulated at the hypothalamic level by the suprachiasmatic nuclei (SCN). This central oscillator transduces photic information to the cellular clocks in the periphery through the autonomic nervous system and the neuroendocrine system. The fact that these two systems have been shown to modulate leukocyte physiology supports the concept that the circadian component is an important aspect of hypothalamic-immune communication. Circadian disruption has been linked to immune dysregulation, and recent reports suggest that several circadian clock genes, in addition to their time-keeping role, are involved in the immune response. In this overview, we summarize the findings demonstrating that Natural Killer (NK) cell function is under circadian control.

Clock gene expression in the murine gastrointestinal tract: endogenous rhythmicity and effects of a feeding regimen

BACKGROUND & AIMS

Based on observations that the gastrointestinal tract is subject to various 24-hour rhythmic processes, it is conceivable that some of these rhythms are under circadian clock gene control. We hypothesized that clock genes are present in the gastrointestinal tract and that they are part of a functional molecular clock that coordinates rhythmic physiologic functions.

METHODS

The effects of timed feeding and vagotomy on temporal clock gene expression (clock, bmal1, per1-3, cry1-2) in the gastrointestinal tract and suprachiasmatic nucleus (bmal, per2) of C57BL/6J mice were examined using real-time polymerase chain reaction and Western blotting (BMAL, PER2). Colonic clock gene localization was examined using immunohistochemistry (BMAL, PER1-2).

RESULTS

Clock immunoreactivity was observed in the myenteric plexus and epithelial crypt cells. Clock genes were expressed rhythmically throughout the gastrointestinal tract. Timed feeding shifted clock gene expression at the RNA and protein level but did not shift clock gene expression in the central clock. Vagotomy did not alter gastric clock gene expression compared with sham-treated controls.

CONCLUSIONS

The murine gastrointestinal tract contains functional clock genes, which are molecular core components of the circadian clock. Daytime feeding in nocturnal rodents is a strong synchronizer of gastrointestinal clock genes. This synchronization occurs independently of the central clock. Gastric clock gene expression is not mediated through the vagal nerve. The presence of clock genes in the myenteric plexus and epithelial cells suggests a role for clock genes in circadian coordination of gastrointestinal functions such as motility, cell proliferation, and migration.

Chronobiology and chronotherapy of ischemic heart disease

The occurrence of the clinical manifestations of ischemic heart disease (IHD)--myocardial ischemia and angina pectoris, acute myocardial infarction, and sudden cardiac death--is unevenly distributed during the 24 h with greater than expected events during the initial hours of the daily activity span and in the late afternoon or early evening. Such temporal patterns result from circadian rhythms in pathophysiological mechanisms plus cyclic environmental stressors that trigger ischemic events. Both the pharmacokinetics (PK) and pharmacodynamics (PD) of many, though not all, anti-ischemic oral nitrate, calcium channel blocker, and beta-adrenoceptor antagonist medications have been shown to be influenced by the circadian time of their administration. The requirement for preventive and therapeutic interventions varies predictably during the 24 h, and thus therapeutic strategies should also be tailored accordingly to optimize outcomes. During the past decade, two first generation calcium channel blocker chronotherapies have been developed, trialed, and marketed in North America for the improved treatment of IHD. Nonetheless, there has been relatively little investigation of the administration-time (circadian rhythm) dependencies of the PK and PD of conventional anti-ischemic medications, and there has been little progress in the development of new generation IHD chronotherapies. Available epidemiologic, pharmacologic, and clinico-therapeutic evidence demonstrates how the chronobiologic approach to IHD can contribute new insight and opportunities to improve drug design and drug delivery to enhance therapeutic outcomes.

Chronobiology, drug delivery, and chronotherapeutics

Biological processes and functions are organized in space, as a physical anatomy, and time, as a biological time structure. The latter is expressed by short-, intermediate-, and long-period oscillations, i.e., biological rhythms. The circadian (24-h) time structure has been most studied and shows great importance to the practice of medicine and pharmacotherapy of patients. The phase and amplitude of key physiological and biochemical circadian rhythms contribute to the known predictable-in-time patterns in the occurrence of serious and life-threatening medical events, like myocardial infraction and stroke, and the manifestation and severity of symptoms of chronic diseases, like allergic rhinitis, asthma, and arthritis. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and, most important to the theme of this special issue, medications. Rhythmicity in the pathophysiology of disease is one basis for chronotherapeutics--purposeful variation in time of the concentration of medicines in synchrony with biological rhythm determinants of disease activity--to optimize treatment outcomes. A second basis is the control of undesired effects of medications, especially when the therapeutic range is narrow and the potential for adverse effects high, which is the case for cancer drugs. A third basis is to meet the biological requirements for frequency-modulated drug delivery, which is the case for certain neuroendocrine peptide analogues. Great progress has been realized with hydrogels, and they offer many advantages and opportunities in the design of chronotherapeutic systems for drug delivery via the oral, buccal, nasal, subcutaneous, transdermal, rectal, and vaginal routes. Nonetheless, innovative delivery systems will be necessary to ensure optimal application of chronotherapeutic interventions. Next generation drug-delivery systems must be configurable so they (i) require minimal volitional adherence, (ii) respond to sensitive biomarkers of disease activity that often vary in time as periodic (circadian rhythmic) and non-periodic (random) patterns to release medication to targeted tissue(s) on a real time as needed basis, and (iii) are cost-effective.

Emerging links between the biological clock and the DNA damage response

For life forms to survive, they must adapt to their environmental conditions. One such factor that impacts on both prokaryotic and eukaryotic organisms is the light-dark cycle, a consequence of planetary rotation in relation to our sun. In mammals, the daily light cycle has affected the regulation of many cellular processes such as sleep-wake and calorific intake activities, hormone secretion, blood pressure and immune system responses. Such rhythmic behaviour is the consequence of circadian rhythm/biological clock (BC) systems which are controlled in a light stimulus-dependent manner by a master clock called the suprachiasmatic nucleus (SCN) situated within the anterior hypothalamus. Peripheral clocks located in other organs such as the liver and kidneys relay signals from the SCN, which ultimately leads to tightly controlled expression of several protein families that in turn act on a broad range of cellular functions. Work in lower organisms has demonstrated a link between aging processes and BC factors, and studies in both animal models and clinical trials have postulated a role for certain BC-associated proteins in tumourigenesis and cancer progression. Recent exciting data reported within the last year or so have now established a molecular link between specific BC proteins and factors that control the mammalian cell cycle and DNA damage checkpoints. This mini review will focus on these discoveries and emphasise how such BC proteins may be involved, through their interplay with cell cycle/DNA damage response pathways, in the development of human disease such as cancer.

Prevention of melatonin suppression by nocturnal lighting: relevance to cancer

The decreased melatonin production in humans and animals caused by environmental lighting, especially short wavelength lighting (between 470 and 525 nm) has been shown to be associated with an increased risk of cancer. The purpose of this study was to investigate whether blocking light in this wavelength range under bright light may prevent the suppression of melatonin, which could help to prevent cancer. Optical filter lenses were designed, allowing selective exclusion of all wavelengths below 530 nm. Salivary melatonin levels were measured under dim light (<5 lux), bright light (800 lux) and filtered light (800 lux) at hourly intervals between 2000 and 0800 h in 11 healthy young male participants (mean age 23.5+/-1.5 years). The measurements were taken during three nonconsecutive nights over a 2-week period. The Dim Light Melatonin Onset test was used as a marker of circadian phase. Nine of the 11 participants demonstrated preserved melatonin levels in filtered light similar to their dim light secretion profile. With filtered light, the participants had a mean relative amount of melatonin of 91.2 (P>0.05 between dim light and experimental condition). Unfiltered bright light drastically suppressed melatonin production with a mean relative amount of melatonin of 25.4 (P<0.05 between dim light and experimental condition). Preventing melatonin deficiencies using lenses that block light of low wavelength from reaching the retina presents a cost-effective, practical solution to the problem of increased malignancy rates in shift workers.

Working on atypical schedules

Shift work has been associated with a number of health problems including cardiovascular disease, impaired glucose and lipid metabolism, gastrointestinal discomfort, reproductive difficulties, and breast cancer. The specific contributions of disturbed physiological rhythms, circadian misalignment, and sleep debt to the various medical problems encountered by shift workers remain to be clarified. Fatigue can be caused by extended on-duty and/or waking periods, inadequate sleep quantity, sleep disturbances, disruption of circadian rhythms, and difficult work and familial conditions. Fatigue-related accidents raise a safety concern for shift workers, especially at the end of the night when the circadian nadir of alertness interacts with increased time awake. Individuals vary greatly in their capacity to adjust to atypical work schedules and their tolerance to circadian misalignment. Predisposing individual and domestic factors have been identified, such as increasing age, being a single woman in charge of children, and split sleep patterns, all of which can affect the ability to adjust to atypical schedules. However, prior studies indicate that predisposing individual and social determinants are generally poor predictors of shift work tolerance in a given individual. In this manuscript, we review several countermeasures to improve adaptation to shift work.

Nutritional and lifestyle correlates of the cancer-protective hormone melatonin

CONTEXT

Despite growing support for melatonin as a promising agent for cancer treatment and possibly cancer prevention, few studies have elucidated factors that influence endogenous melatonin. This overview summarizes dietary and lifestyle factors that have been shown to affect circulating melatonin levels.

BIOLOGICAL MECHANISMS

To date, many animal studies and in vitro experiments have illustrated that melatonin possesses oncostatic activity. Mechanisms that are currently being studied include melatonin's activity as an indirect antioxidant and free radical scavenger; its action on the immune system; suppression of fatty acid uptake and metabolism; and its ability to increase the degradation of calmoduline and to induce apoptosis. Studies further suggest that melatonin reduces local estrogen synthesis, through down-regulation of the hypothalamic-pituitary reproductive axis and direct actions of melatonin at the tumor cell level, thus behaving as a SERM.

THERAPEUTIC APPLICATIONS

Several small clinical trials have demonstrated that melatonin has some potential, either alone or in combination with standard cancer therapy, to yield favorable responses. Melatonin or its precursor tryptophan have been found in numerous edible plants, but more studies are needed to evaluate the influence of diets rich in tryptophan and melatonin on circulating melatonin levels in humans. Age, BMI, parity, and the use of certain drugs remain the factors that have been associated most consistently with aMT6s levels.

DISCUSSION

Further insights into the effects of dietary and lifestyle factors that modulate circulating melatonin levels may provide the basis for novel interventions to exploit melatonin for the prevention and treatment of human diseases.

[Circadian behaviour of host versus tumour outcome. A review]

The authors reviewed experimental and clinical data emphasizing the importance for host to keep a reference circadian rythmicity. This assessment seems true both in the cancerogenesis phase, as well in the active phase of tumoural disease.

Diurnal urinary 6-sulfatoxymelatonin levels among healthy Danish nurses during work and leisure time

The present study aims to examine the influence of evening and night shift work, compared to day shift work, on melatonin secretion in nurses in a field setting. Effects were examined during a workday and during a day off. Both fixed schedules and mixed or rotating schedules were studied. In total, 170 nurses were studied: 89 nurses worked fixed schedules, 27 nurses worked the day shift, 12 nurses worked the evening shift, 50 nurses worked the night shift, and 82 nurses worked mixed schedules, with data collected during a day (n = 17), evening (n = 14), or night shift (n = 50). All spot urine samples were collected during 24 h from the participants on a work day and on a day off and were analyzed for 6-sulphatoxymelatonin. On the day of urine sampling, participants filled in the Karolinska Sleep Diary. Additional information was collected through a telephone interview. Data were analyzed using a mixed procedure with autoregressive covariance structure. The present study showed that shift work affected the concentrations of 6-sulphatoxymelatonin in the short term by lower excretion in urine from nurses working the night compared to day shift on a workday and on a day off as well. No significant differences were observed between a workday and a day off when doing day and evening shifts, irrespective of mixed and fixed schedules. Sleep length was reduced workdays (from 6.1-6.8 h) among all nurses, compared to days off (from 7.8-8.7 h).

Impact of Shift Work on the Health and Safety of Nurses and Patients

Shift work generally is defined as work hours that are scheduled outside of daylight. Shift work disrupts the synchronous relationship between the body's internal clock and the environment. The disruption often results in problems such as sleep disturbances, increased accidents and injuries, and social isolation. Physiologic effects include changes in rhythms of core temperature, various hormonal levels, immune functioning, and activity-rest cycles. Adaptation to shift work is promoted by reentrainment of the internally regulated functions and adjustment of activity-rest and social patterns. Nurses working various shifts can improve shift-work tolerance when they understand and adopt counter measures to reduce the feelings of jet lag. By learning how to adjust internal rhythms to the same phase as working time, nurses can improve daytime sleep and family functioning and reduce sleepiness and work-related errors. Modifying external factors such as the direction of the rotation pattern, the number of consecutive night shifts worked, and food and beverage intake patterns can help to reduce the negative health effects of shift work. Nurses can adopt counter measures such as power napping, eliminating overtime on 12-hour shifts, and completing challenging tasks before 4 am to reduce patient care errors.

Melatonin in cancer management: progress and promise

Physiologic and pharmacologic concentrations of the pineal hormone melatonin have shown chemopreventive, oncostatic, and tumor inhibitory effects in a variety of in vitro and in vivo experimental models of neoplasia. Multiple mechanisms have been suggested for the biological effects of melatonin. Not only does melatonin seem to control development alone but also has the potential to increase the efficacy and decrease the side effects of chemotherapy when used in adjuvant settings. This review critically evaluates progress in the ability of melatonin to prevent or reverse cancer development and progression. We also discuss future prospects of the possible development of melatonin as a chemopreventive agent.

Seasonal Shedding ofEscherichia coliO157:H7 in Ruminants: A New Hypothesis

Seasonal shedding of Escherichia coli O157:H7 in ruminants is well documented; however, viable explanations for this phenomenon are lacking. The fecal prevalence of E. coli O157:H7 in ruminants is the highest in the summer months, decreasing to low or undetectable levels in the winter. To determine if day length is correlated to seasonal shedding, nine reports of E. coli O157:H7 prevalence in cattle were selected for similarity of sampling technique, culture methodology, cattle type, and ability to determine approximate sampling month and location, representing three regions in North America (southern Canada, midwestern United States, and the southern United States/Mexico). Correlation and regression analysis revealed a positive correlation existed between day length (r = 0.67; R2 = 0.45; P = 0.0009) and, to a lesser extent, ambient temperature (r = 0.43; R2 = 0.19; P = 0.05) and E. coli O157:H7 prevalence. Based on these results, a study was conducted in a commercial feedlot to examine the effect of artificial lighting on E. coli O157 prevalence. Four pens of cattle received approximately 5 hours of artificial lighting daily (in addition to the natural light) for 60 days and four pens served as controls. Freshly voided fecal samples (representing approximately 30% of the steers/pen) were collected from the pen floor and cultured for E. coli O157 after 25 and 53 days of artificial lighting and 28 and 43 days following cessation of the lighting treatment. Fecal prevalence of E. coli O157 remained constant in the lighted pens whereas prevalence was lower (P < 0.01) in the control treatment after 53 days of lighting. Forty-three days following cessation of the lighting treatment, prevalence decreased in the lighted treatment group to levels comparable (P > 0.20) to control levels. Understanding the mechanisms underlying the seasonality of this important foodborne pathogen will enable the implementation of effective control strategies when it is most prevalent.

Improved Tumor Control through Circadian Clock Induction by Seliciclib, a Cyclin-Dependent Kinase Inhibitor

The circadian timing system and the cell division cycle are frequently deregulated in cancer. The therapeutic relevance of the reciprocal interactions between both biological rhythms was investigated using Seliciclib, a cyclin-dependent kinase (CDK) inhibitor (CDKI). Mice bearing Glasgow osteosarcoma received Seliciclib (300 mg/kg/d orally) or vehicle for 5 days at Zeitgeber time (ZT) 3, 11, or 19. On day 6, tumor mRNA 24-hour expression patterns were determined for clock genes (Per2, Rev-erbalpha, and Bmal1) and clock-controlled cell cycle genes (c-Myc, Wee1, cyclin B1, and CDK1) with quantitative reverse transcription-PCR. Affinity chromatography on immobilized Seliciclib identified CDK1/CDK2 and extracellular signal-regulated kinase (ERK) 1/ERK2, CDK7/CDK9, and casein kinase CK1epsilon as Seliciclib targets, which respectively regulate cell cycle, transcription, and circadian clock in Glasgow osteosarcoma. Seliciclib reduced tumor growth by 55% following dosing at ZT3 or ZT11 and by 35% at ZT19 compared with controls (P < 0.001). Tolerability was also best at ZT3. Mean transcriptional activity of Rev-erbalpha, Per2, and Bmal1 was arrhythmic in the tumors of untreated mice. Seliciclib induced rhythmic clock gene expression patterns with physiologic phase relations only after ZT3 dosing. c-Myc and Wee1 mRNAs displayed synchronous circadian rhythms in the tumors of control mice receiving vehicle only but not in those of mice given the drug. Seliciclib further enhanced Wee1 expression irrespective of dosing time, an effect that reinforced G(2)-M gating. Seliciclib also inhibited CK1epsilon, which determines circadian period length. The coordination of clock gene expression patterns in tumor cells was associated with best antitumor activity of Seliciclib. The circadian clock and its upstream regulators represent relevant targets for CDKIs.

Longitudinal relationship of work hours, mandatory overtime, and on-call to musculoskeletal problems in nurses

BACKGROUND

Nurses are at very high risk for work-related musculoskeletal injury/disorders (MSD) with low back pain/injury being the most frequently occurring MSD. Nurses are also likely to work extended schedules (long hours, on-call, mandatory overtime, working on days off). The purpose of this study was to examine the relationship of extended work schedules in nurses to MSD.

METHODS

Using a longitudinal, three wave survey of 2,617 registered nurses, Wave 1 work schedule data were related to neck, shoulder, and back (MSD) cases occurring in Waves 2 or 3.

RESULTS

Schedule characteristics increasing MSD risk included 13+ hour/days, off-shifts, weekend work, work during time off (while sick, on days off, without breaks), and overtime/on-call. These increases in risk were not explained by psychological demands, but were largely explained by physical demands.

CONCLUSIONS

Adverse schedules are significantly related to nurse MSD. Healthier schedules, less overtime, and reducing work on days off would minimize risk and recovery time.

Stress sensitivity in metastatic breast cancer: analysis of hypothalamic-pituitary-adrenal axis function

The normal diurnal cortisol cycle has a peak in the morning, decreasing rapidly over the day, with low levels during the night, then rising rapidly again to the morning peak. A pattern of flatter daytime slopes has been associated with more rapid cancer progression in both animals and humans. We studied the relationship between the daytime slopes and other daytime cortisol responses to both pharmacological and psychosocial challenges of hypothalamic-pituitary-adrenal (HPA) axis function as well as DHEA in a sample of 99 women with metastatic breast cancer, in hopes of elucidating the dysregulatory process. We found that the different components of HPA regulation: the daytime cortisol slope, the rise in cortisol from waking to 30 min later, and cortisol response to various challenges, including dexamethasone (DEX) suppression, corticotrophin releasing factor (CRF) activation, and the Trier Social Stress Task, were at best modestly associated. Escape from suppression stimulated by 1mg of DEX administered the night before was moderately but significantly associated with flatter daytime cortisol slopes (r=0.28 to .30 at different times of the post DEX administration day, all p<.01). Daytime cortisol slopes were also moderately but significant associated with the rise in cortisol from waking to 30 min after awakening (r=.29, p=.004, N=96), but not with waking cortisol level (r=-0.13, p=.19). However, we could not detect any association between daytime cortisol slope and activation of cortisol secretion by either CRF infusion or the Trier Social Stress Task. The CRF activation test (following 1.5mg of DEX to assure that the effect was due to exogenous CRF) produced ACTH levels that were correlated (r=0.66, p<.0001, N=74) with serum cortisol levels, indicating adrenal responsiveness to ACTH stimulation. Daytime cortisol slopes were significantly correlated with the slope of DHEA (r=.21, p=.04, N=95). Our general findings suggest that flatter daytime cortisol slopes among metastatic breast cancer patients may be related to disrupted feedback inhibition rather than hypersensitivity in response to stimulation.

Biological clocks and shift work: circadian dysregulation and potential long-term effects

Long-term epidemiologic studies on large numbers of night and rotating shift workers have suggested an increase in the incidence of breast and colon cancer in these populations. These studies suffer from poor definition and quantification of the work schedules of the exposed subjects. Against this background, the pathophysiology of phase shift and phase adaptation is reviewed. A phase shift as experienced in night and rotating shift work involves desynchronization at the molecular level in the circadian oscillators in the central nervous tissue and in most peripheral tissues of the body. There is a change in the coordination between oscillators with transient loss of control by the master-oscillator (the Suprachiasmatic Nucleus, SCN) in the hypothalamus. The implications of the pathophysiology of phase shift are discussed for long-term health effects and for the design of ergonomic work schedules minimizing the adverse health effects upon the worker.

Evidence supporting a circadian control of natural killer cell function

Natural killer (NK) cells participate in the immune response against infection and cancer. An emerging body of epidemiological data supports that circadian homeostasis may constitute a factor risk for cancer development. Physiological rhythms under circadian control persist in the absence of light entrainment and ultimately rely on a molecular clock. We have previously shown that NK cell cytolytic activity follows a daily rhythm and that NK cells enriched from light-entrained rats present 24-h oscillations of clock genes, cytolytic factors, and cytokines. To investigate whether these oscillations are under a genuine circadian control, we assessed the daily expression of clock genes (Per1, Per2, Clock, and Bmal1), a clock-controlled gene (Dbp), cytolytic factors (granzyme B and perforin), and cytokines (IFN-gamma and TNF-alpha) in NK cells enriched from rats maintained in constant darkness (DD). In addition, we investigated whether the disruption of the NK cell clock by RNA interference (RNAi) affects the expression of cytolytic factors and cytokines. Persistent 24-h oscillations were found in the expression levels of clock genes, cytolytic factors, and cytokines in NK cells enriched from DD rats. In addition, RNAi-mediated Per2 knockdown caused a significant decrease of granzyme B and perforin levels in the rat derived NK cell line RNK16. Taken together, these results provide evidence supporting that NK cell function is under circadian regulation.

The circadian gene mPer2 regulates the daily rhythm of IFN-gamma

Circadian and daily rhythms regulate many aspects of physiology and behavior. Although a growing number of studies suggest that circadian disruptions may render organisms more susceptible to infection and cancer, the molecular links between the circadian system and the immune system are largely unknown. Here we report that mice carrying a loss-of-function mutation in the Per2 gene, a key component of the molecular circadian clock, lacked the physiologic daily rhythm of interferon-gamma (IFN-gamma) mRNA and protein expression in the spleen. These observations were associated with a significant alteration in the expression of canonical clock genes. In addition, Per2 mutant mice failed to show a daily rhythm in IFN-gamma serum levels, which were significantly lower than those determined in wild-type mice during the early light period. These findings provide novel evidence for a direct circadian regulation of IFN-gamma, a critical cytokine modulating the immune response.

Shift work, light at night, and breast cancer on Long Island, New York

The hypothesized association between breast cancer and circadian disruption was evaluated in the Electromagnetic Fields and Breast Cancer on Long Island Study. Participants included 576 women with breast cancer diagnosed from August 1996 to June 1997 and 585 population-based controls (87% and 83% participation rates, respectively) aged < 75 years and living in the same Long Island, New York, home for > or = 15 years. An in-person interview ascertained light-at-night exposure histories through shift work (previous 15 years) and at home (previous 5 years). Odds ratios and 95% confidence intervals were estimated by unconditional multivariate logistic regression. Breast cancer was not associated with overall shift work (odds ratio (OR) = 1.04, 95% confidence interval (CI): 0.79, 1.38) or evening shift work (OR = 1.08, 95% CI: 0.81, 1.44). However, overnight shift workers were at lower risk than women never working shifts (OR = 0.55, 95% CI: 0.32, 0.94). Women who frequently turned on lights at home during sleep hours (> or = twice/week and > or = twice/night) had increased risks (OR = 1.65, 95% CI: 1.02, 2.69). The latter results suggest positive associations with residential light-at-night exposure, or they could reflect response biases. Furthermore, overall and evening shift work were not significant factors, and analyses of overnight shift workers yielded reduced risk estimates. The study thus provides mixed evidence for the light-at-night hypothesis.

The circadian gene per1 plays an important role in cell growth and DNA damage control in human cancer cells

The Per1 gene is a core clock factor that plays an essential role in generating circadian rhythms. Recent data reveal that major biological pathways, including those critical to cell division, are under circadian control. We report here that Per1 provides an important link between the circadian system and the cell cycle system. Overexpression of Per1 sensitized human cancer cells to DNA damage-induced apoptosis; in contrast, inhibition of Per1 in similarly treated cells blunted apoptosis. The apoptotic phenotype was associated with altered expression of key cell cycle regulators. In addition, Per1 interacted with the checkpoint proteins ATM and Chk2. Ectopic expression of Per1 in human cancer cell lines led to significant growth reduction. Finally, Per1 levels were reduced in human cancer patient samples. Our results highlight the importance of circadian regulation to fundamental cellular functions and support the hypothesis that disruption of core clock genes may lead to cancer development.

Violet and blue light blocking intraocular lenses: photoprotection versus photoreception

AIM

To analyse how intraocular lens (IOL) chromophores affect retinal photoprotection and the sensitivity of scotopic vision, melanopsin photoreception, and melatonin suppression.

METHODS

Transmittance spectra of IOLs, high pass spectral filters, human crystalline lenses, and sunglasses are used with spectral data for acute ultraviolet (UV)-blue photic retinopathy ("blue light hazard" phototoxicity), aphakic scotopic luminous efficiency, melanopsin sensitivity, and melatonin suppression to compute the effect of spectral filters on retinal photoprotection, scotopic sensitivity, and circadian photoentrainment.

RESULTS

Retinal photoprotection increases and photoreception decreases as high pass filters progressively attenuate additional short wavelength light. Violet blocking IOLs reduce retinal exposure to UV (200-400 nm) radiation and violet (400-440 nm) light. Blue blocking IOLs attenuate blue (440-500 nm) and shorter wavelength optical radiation. Blue blocking IOLs theoretically provide better photoprotection but worse photoreception than conventional UV only blocking IOLs. Violet blocking IOLs offer similar UV-blue photoprotection but better scotopic and melanopsin photoreception than blue blocking IOLs. Sunglasses provide roughly 50% more UV-blue photoprotection than either violet or blue blocking IOLs.

CONCLUSIONS

Action spectra for most retinal photosensitisers increase or peak in the violet part of the spectrum. Melanopsin, melatonin suppression, and rhodopsin sensitivities are all maximal in the blue part of the spectrum. Scotopic sensitivity and circadian photoentrainment decline with ageing. UV blocking IOLs provide older adults with the best possible rhodopsin and melanopsin sensitivity. Blue and violet blocking IOLs provide less photoprotection than middle aged crystalline lenses, which do not prevent age related macular degeneration (AMD). Thus, pseudophakes should wear sunglasses in bright environments if the unproved phototoxicity-AMD hypothesis is valid.

Disruption of Circadian Coordination and Malignant Growth

Altered circadian rhythms predicted for poor survival in patients with metastatic colorectal or breast cancer. An increased incidence of cancers has been reported in flying attendants and in women working predominantly at night. To explore the contribution of circadian structure to tumor growth we ablated the 24-h rest-activity cycle and markedly altered the rhythms in body temperature, serum corticosterone and lymphocyte count in mice by complete stereotaxic destruction of the suprachiasmatic nuclei (SCN) or by subjecting the mice to experimental chronic jet-lag. Such disruption of circadian coordination significantly accelerated malignant growth in two transplantable tumor models, Glasgow osteosarcoma and Pancreatic adenocarcinoma. The mRNA expression of clock genes per2 and reverb-alpha in controls displayed significant circadian rhythms in the liver (Cosinor, p=0.006 and p=0.003, respectively) and in the tumor (p=0.04 and p<0.001, respectively). Both rhythms were suppressed in the liver and in the tumor of jet lagged mice. This functional disturbance of molecular clock resulted in down regulation of p53 and overexpression of c-Myc, two effects which may favor cancer growth.

CONCLUSIONS

These results indicate that circadian system could play an important role in malignant growth control. This should be taken into consideration in cancer prevention and therapy.

Artificial Lighting in the Industrialized World: Circadian Disruption and Breast Cancer

Breast cancer risk is high in industrialized societies, and increases as developing countries become more Westernized. The reasons are poorly understood. One possibility is circadian disruption from aspects of modern life, in particular the increasing use of electric power to light the night, and provide a sun-free environment during the day inside buildings. Circadian disruption could lead to alterations in melatonin production and in changing the molecular time of the circadian clock in the suprachiasmatic nuclei (SCN). There is evidence in humans that the endogenous melatonin rhythm is stronger for persons in a bright-day environment than in a dim-day environment; and the light intensity necessary to suppress melatonin at night continues to decline as new experiments are done. Melatonin suppression can increase breast tumorigenesis in experimental animals, and altering the endogenous clock mechanism may have downstream effects on cell cycle regulatory genes pertinent to breast tissue development and susceptibility. Therefore, maintenance of a solar day-aligned circadian rhythm in endogenous melatonin and in clock gene expression by exposure to a bright day and a dark night, may be a worthy goal. However, exogenous administration of melatonin in an attempt to achieve this goal may have an untoward effect given that pharmacologic dosing with melatonin has been shown to phase shift humans depending on the time of day it's given. Exogenous melatonin may therefore contribute to circadian disruption rather than alleviate it.

The Anti-tumor Activity of Pineal Melatonin and Cancer Enhancing Life Styles in Industrialized Societies

This review discusses the potential role of the anti-tumor activity of pineal melatonin for the aetiology and prevention of cancers related to life-styles in industrialized societies, e.g. frequent long-distance flights as well as chronic night shift work leading to circadian disturbances of neuroendocrine parameters including melatonin. Experimental studies show that melatonin controls not only the growth of well-differentiated cancers, but also possesses anti-carcinogenic properties. Therefore, it is plausible that disturbances of circadian melatonin rhythmicity could be functionally involved in elevated cancer risks among aircrew members and nurses frequently working on night shifts. Due to the suppression of melatonin by light it can be assumed that too much artificial light at night could, at least in part, be responsible for generally increasing rates of e.g. breast cancer in industrialized countries. It is discussed under which conditions a transient substitutional therapy with melatonin could be justified or which forms of living could help to physiologically foster melatonin secretion to optimise control over cancerous growth and development.

Microarray analysis of transcription factor gene expression in melatonin-treated human peripheral blood mononuclear cells

The existence of specific melatonin-binding sites in lymphoid cells led to the discovery of signal transduction pathway for melatonin in human lymphocytes and immunomodulatory role of melatonin in immune cells. In recent years, transcriptional regulation of melatonin on various transcription factors has been demonstrated. Therefore, this study was designed to assess by cDNA microarray analysis the regulatory effects of melatonin on transcription factors in human peripheral blood mononuclear cells (PBMCs). Forty-six genes were upregulated and 23 were downregulated more than twofold in melatonin-treated PBMCs. Of the more than twofold upregulated transcription factor genes, homeo box A4 (HOXA4), forkhead box O1A (FOXO1A), transcription elongation factor B (SIII), polypeptide 3 (TCEB3), and peroxisome proliferative activated receptor delta (PPARD) were identified. Of the more than twofold downregulated genes, PHD finger protein 15 (PHF15) and zinc finger protein 33a (ZNF33A) were identified. In summary, identification of these genes by cDNA microarray analysis in response to melatonin administration may provide a foundation for further studies on the function of melatonin in human PBMCs.

Circadian Disruption, Shift Work and the Risk of Cancer: A Summary of the Evidence and Studies in Seattle

There is increasing interest in the possibility that disruption of normal circadian rhythm may increase the risk of developing cancer. Persons who engage in nightshift work may exhibit altered nighttime melatonin levels and reproductive hormone profiles that could increase the risk of hormone-related diseases, including breast cancer. Epidemiologic studies are now beginning to emerge suggesting that women who work at night, and who experience sleep deprivation, circadian disruption, and exposure to light-at-night are at an increased risk of breast cancer, and possibly colorectal cancer as well. Several studies have been conducted in Seattle recently to investigate the effects of factors that can disrupt circadian rhythm and alter normal nocturnal production of melatonin and reproductive hormones of relevance to breast cancer etiology. Studies completed to date have found: (1) an increased risk of breast cancer associated with indicators of exposure to light-at-night and night shift work; and (2) decreased nocturnal urinary levels of 6-sulphatoxymelatonin associated with exposure to 60-Hz magnetic fields in the bedroom the same night, and a number of other factors including hours of daylight, season, alcohol consumption and body mass index. Recently completed is an experimental crossover study designed to investigate whether exposure to a 60-Hz magnetic field under controlled conditions in the home sleeping environment is associated with a decrease in nocturnal urinary concentration of 6-sulphatoxymelatonin, and an increase in the urinary concentration of luteinizing hormone, follicle stimulating hormone, and estradiol in a sample of healthy women of reproductive age. Presently underway is a study to determine whether working at night is associated with decreased levels of urinary 6-sulphatoxymelatonin, and increased urinary concentrations of the reproductive hormones listed above in a sample of healthy women of reproductive age, and to elucidate characteristics of sleep among night shift workers that are related to the hormone patterns identified. A proposal is under review to extend these studies to a sample of healthy men to investigate whether working at night is associated with decreased levels of urinary 6-sulphatoxymelatonin, and increased concentrations of urinary cortisol and cortisone, urinary levels of a number of androgen metabolites, and serum concentrations of a number of reproductive hormones. Secondarily, the proposed study will elucidate characteristics of sleep among night shift workers that are related to the hormone patterns identified, as well as investigate whether polymorphisms of the genes thought to regulate the human circadian clock are associated with the ability to adapt to night shift work. It is anticipated that collectively these studies will enhance our understanding of the role of circadian disruption in the etiology of cancer.

A prospective study of night shift work, sleep duration, and risk of Parkinson's disease

The authors prospectively investigated whether working rotating night shifts was associated with the risk of Parkinson's disease among 84,794 female nurses who reported years of night shift work in 1988 (the US Nurses' Health Study). After 975,912 person-years of follow-up (1988-2000), 181 incident Parkinson's disease cases were documented. Compared with nurses who never worked rotating night shifts, those with 15 years or more of night shift work had a 50% lower risk of Parkinson's disease after adjustment for age and smoking (95% confidence interval: 0.26, 0.97; p(trend) = 0.01). Sleep duration was positively associated with Parkinson's disease risk: The relative risk was 1.84 (95% confidence interval: 0.99, 3.42) when comparing nurses who reported 9 or more hours of sleep per day with those who slept 6 hours or less (p(trend) = 0.005). These data suggest that working night shifts may be protective against Parkinson's disease or that low tolerance for night shift work is an early marker of Parkinson's disease. Conversely, habitual longer sleep duration may be an earlier marker of Parkinson's disease. Because of the novelty and the exploratory nature of these findings, confirmation is needed.

The influence of bio-behavioural factors on tumour biology: pathways and mechanisms

Epidemiological studies indicate that stress, chronic depression and lack of social support might serve as risk factors for cancer development and progression. Recent cellular and molecular studies have identified biological processes that could potentially mediate such effects. This review integrates clinical, cellular and molecular studies to provide a mechanistic understanding of the interface between biological and behavioural influences in cancer, and identifies novel behavioural or pharmacological interventions that might help improve cancer outcomes.