Rotating night shift work and the risk of ischemic stroke

Night shift work and levels of 6-sulfatoxymelatonin and cortisol in men

BACKGROUND

Night shift work is associated with cancer among men, but the biologic mechanism is unclear. We investigated whether male night shift workers showed changes in levels of melatonin and cortisol, potential biomarkers of cancer risk.

METHODS

Urine was collected from 185 night shift and 158 day shift-working male healthcare providers, aged 22 to 55 years, throughout work and sleep periods, and assayed for 6-sulfatoxymelatonin and cortisol. Morning serum was collected within 90 minutes of completing the night and assayed for cortisol.

RESULTS

Night shift workers had significantly lower 6-sulfatoxymelatonin levels during daytime sleep, nighttime work, and nighttime sleep on off-nights (57%, 62%, and 40% lower, respectively), relative to the day shift workers during nighttime sleep (P < 0.0001); urinary cortisol in night shift workers was 16% higher during daytime sleep and 13% lower during nighttime sleep on off-nights (P < 0.05). Morning serum cortisol post-work and post-sleep in night shift workers were 24% and 43% lower, respectively, than post-sleep levels among day shift workers (P < 0.0001). Within-subject comparisons among the night shift workers revealed significantly lower melatonin levels and significantly higher urinary cortisol levels during daytime sleep and nighttime work, relative to nighttime sleep (P < 0.01); morning serum cortisol levels post-work were lower than those post-sleep.

CONCLUSIONS

Night shift workers have substantially lower 6-sulfatoxymelatonin during night work and daytime sleep, and levels remain low when night shift workers sleep at night. Chronic reduction in melatonin among night shift workers may be an important carcinogenic mechanism. Cortisol secretion patterns may be impacted by night shift work, which could affect cancer risk.

IMPACT

Shift work could be an important risk factor for many types of cancer.

Influences of early shift work on the diurnal cortisol rhythm, mood and sleep: within-subject variation in male airline pilots

We aimed to investigate how early and late work shifts influenced the diurnal cortisol rhythm using a within-subjects study design. Participants were 30 healthy male non-smoking pilots, mean age 39.4, employed by a short-haul airline. The standard rotating shift pattern consisted of 5 early shifts (starting before 0600 h), followed by 3 rest days, 5 late shifts (starting after 1200 h) and 4 rest days. Pilots sampled saliva and completed subjective mood ratings in a logbook 6 times over the day on two consecutive early shift days, two late days and two rest days. Sampling was scheduled at waking, waking+30 m, waking+2.5 h, waking+8 h, waking+12 h and bedtime. Waking time, sleep duration, sleep quality and working hours were also recorded. Cortisol responses were analysed with repeated measures analysis of variance with shift condition (early, late, rest) and sample time (1-6) as within-subject factors. Early shifts were associated with a higher cortisol increase in response to awakening (CAR(i)), a greater total cortisol output over the day (AUC(G)) and a slower rate of decline over the day than late shifts or rest days. Early shifts were also associated with shorter sleep duration but co-varying for sleep duration did not alter the effects of shift on the cortisol rhythm. Both types of work shift were associated with more stress, tiredness and lower happiness than rest days, but statistical adjustment for mood ratings did not alter the findings. Early shift days were associated with significantly higher levels of circulating cortisol during waking hours than late shifts or rest days.

Health consequences of shift work and implications for structural design

The objective of the study was to perform a literature review on the health consequences of working rotating shifts and implications for structural design. A literature search was performed in June 2012 and a selection of the most relevant peer-review articles was included in the present review. Shift workers are more likely to suffer from a circadian sleep disorder characterized by sleepiness and insomnia. Shift work is associated with decreased productivity, impaired safety, diminished quality of life and adverse effects on health. Circadian disruption resulting from rotating shift work has also been associated with increased risk for metabolic syndrome, diabetes, cardiovascular disease and cancer. This article summarizes the known health effects of shift work and discusses how light can be used as a countermeasure to minimize circadian disruption at night while maintaining alertness. In the context of the lighted environment, implications for the design of newborn intensive care units are also discussed.

Impact of shiftwork on irritable bowel syndrome and functional dyspepsia

Disturbances in biological rhythms could lead to unfavorable health impact. This study aimed to evaluate the prevalence of functional dyspepsia (FD) and irritable bowel syndrome (IBS) in rotating shift workers, and to determine the factors that have significant association with the prevalence of FD and IBS. The research had been carried out among nurses and nursing assistants working at Ewha Womans University Mokdong Hospital between December 2010 and February 2011. The subjects completed self-reported questionnaires, including the quality of the sleep and the level of stress. The prevalence of FD and IBS defined by ROME III criteria, and factors associated the disorders in rotating shift workers were compared with those of day workers. A total of 207 subjects were included in the study with 147 rotating shift workers (71.0%), and 60 (29.0%) day workers. The prevalence of IBS in rotating shift workers was higher than that in day workers (32.7% vs 16.7%, P = 0.026). However, no significant difference in the prevalence of FD was observed between the two groups (19.7% vs 20.0%, P = 0.964). In the multivariate analysis, the risk factors for IBS were rotating shift work (OR, 2.36; 95% CI, 1.01-5.47) and poor sleep quality (OR, 4.13; 95% CI, 1.82-9.40), and the risk factors for FD were poor sleep quality (OR, 2.31; 95% CI, 1.01-5.28), and severe stress (OR, 2.19; 95% CI, 1.06-4.76). A higher prevalence of IBS among rotating shift workers could be directly associated with the circadian rhythm disturbance. The circadian rhythm disturbance may be related with the pathogenesis of IBS.

Sleep loss as risk factor for neurologic disorders: a review

Sleep loss refers to sleep of shorter duration than the average baseline need of seven to eight hours per night. Sleep loss and sleep deprivation have severe effects on human health. In this article, we review the main aspects of sleep loss, taking into account its effects on the central nervous system. The neurocognitive and behavioral effects of sleep loss are well known. However, there is an increasing amount of research pointing to sleep deprivation as a risk factor for neurologic diseases, namely stroke, multiple sclerosis, Alzheimer's disease, headache, epilepsy, pain, and somnambulism. Conversely, sleep loss has been reported to be a potential protective factor against Parkinson's disease. The pathophysiology involved in this relationship is multiple, comprising immune, neuroendocrine, autonomic, and vascular mechanisms. It is extremely important to identify the individuals at risk, since recognition and adequate treatment of their sleep problems may reduce the risk of certain neurologic disorders.

Health consequences of circadian disruption in humans and animal models

Daily rhythms in behavior and physiology are programmed by a hierarchical collection of biological clocks located throughout the brain and body, known as the circadian system. Mounting evidence indicates that disruption of circadian regulation is associated with a wide variety of adverse health consequences, including increased risk for premature death, cancer, metabolic syndrome, cardiovascular dysfunction, immune dysregulation, reproductive problems, mood disorders, and learning deficits. Here we review the evidence for the pervasive effects of circadian disruption in humans and animal models, drawing from both environmental and genetic studies, and identify questions for future research.

Circadian Levels of Serum Melatonin and Cortisol in relation to Changes in Mood, Sleep, and Neurocognitive Performance, Spanning a Year of Residence in Antarctica

Background. Altered circadian cortisol and melatonin rhythms in healthy subjects exposed to an extreme polar photoperiod results in changes in mood and sleep, which can influence cognitive performance. Materials and Methods. We assessed the circadian rhythm of 20 subjects who wintered over at Maitri (70°S, 11°E), India's permanent Antarctic station, from November 2010 to December 2011. Serum cortisol and melatonin levels were measured by radioimmunoassay at 8 am, 3 pm, 8 pm, and 2 am in a single day, once each during the polar summer and winter photoperiods. Conventional psychological tests, Depression, Anxiety, and Stress Scale (DASS-42), Epworth Sleepiness Scale (ESS), and a computerized neurocognitive test battery were used to measure mood, sleep, and cognitive performance. Results. The mean scores for DASS42 were higher during midwinter suggesting the presence of "overwintering." Mean diurnal cortisol levels during summer and winter were comparable, but the levels of melatonin were markedly higher during winter. Higher 8 am melatonin levels were associated with better sleep quality, lower depression scores, and better performance in tasks like attention, visual memory, and arithmetic. Conclusion. Timing of artificial light exposure and usage of melatonin supplements in improving sleep and cognitive performance in expedition teams are of future research interest.

Immunity's fourth dimension: approaching the circadian-immune connection

The circadian system ensures the generation and maintenance of self-sustained ~24-h rhythms in physiology that are linked to internal and environmental changes. In mammals, daily variations in light intensity and other cues are integrated by a hypothalamic master clock that conveys circadian information to peripheral molecular clocks that orchestrate physiology. Multiple immune parameters also vary throughout the day and disruption of circadian homeostasis is associated with immune-related disease. Here, we discuss the molecular links between the circadian and immune systems and examine their outputs and disease implications. Understanding the mechanisms that underlie circadian-immune crosstalk may prove valuable for devising novel prophylactic and therapeutic interventions.

Occupational exposures and mortality from cardiovascular disease among women textile workers in Shanghai, China

BACKGROUND

Exposure to textile fiber dusts, like particulate air pollution, may be associated with cardiovascular disease (CVD) mortality. Bacterial endotoxin, a potent inflammagen found in cotton dust, may be a specific risk factor.

METHODS

Female textile workers (N = 267,400) in Shanghai, China were followed for CVD mortality (1989-2000). Factory exposures were approximated by sector classifications based on materials and processes. Quantitative endotoxin and cotton dust measures were available for a subcohort (n = 3,188). Cox proportional hazards modeling was used to estimate hazard ratios (HR) and 95% confidence interval (CI).

RESULTS

Slightly elevated mortality risk for the cotton sector was seen for ischemic stroke (HR = 1.12, 95% CI: 0.97-1.31) and hemorrhagic stroke (HR = 1.12, 95% CI: 1.02-1.23). Similar hemorrhagic stroke mortality risk was observed in high dust sectors (HR = 1.12, 95% CI: 1.02-1.24). No association was observed for ischemic heart disease.

CONCLUSIONS

Exposures in textile factories may have contributed to CVD mortality among this cohort. The specific components of these exposures that may be harmful are not clear and should be further investigated.

Shift work: health, performance and safety problems, traditional countermeasures, and innovative management strategies to reduce circadian misalignment

There are three mechanisms that may contribute to the health, performance, and safety problems associated with night-shift work: (1) circadian misalignment between the internal circadian clock and activities such as work, sleep, and eating, (2) chronic, partial sleep deprivation, and (3) melatonin suppression by light at night. The typical countermeasures, such as caffeine, naps, and melatonin (for its sleep-promoting effect), along with education about sleep and circadian rhythms, are the components of most fatigue risk-management plans. We contend that these, while better than nothing, are not enough because they do not address the underlying cause of the problems, which is circadian misalignment. We explain how to reset (phase-shift) the circadian clock to partially align with the night-work, day-sleep schedule, and thus reduce circadian misalignment while preserving sleep and functioning on days off. This involves controlling light and dark using outdoor light exposure, sunglasses, sleep in the dark, and a little bright light during night work. We present a diagram of a sleep-and-light schedule to reduce circadian misalignment in permanent night work, or a rotation between evenings and nights, and give practical advice on how to implement this type of plan.

Effects of lifetime exposure to shiftwork on fitness for duty in police officers

Aging and demographic changes in Europe and other global economies have led to a discussion about postponing the legal retirement age; however, health and safety consequences for the workforce have not yet been examined. Thus, the aim of this study was to investigate the effects of lifetime exposure to shiftwork on health impairments and fitness for duty. Two samples of the police force from one of the states of the Federal Republic of Germany were used. One sample was collected in 2008-2009 with a self-administered Internet questionnaire (n = 705); the other sample was derived from employment records provided by the police force of the same federal state for the years 2002-2009 (n = 2460). Both samples contained information about the number of years worked in shiftwork across the entire working life and impairments to fitness for duty assessed by occupational physicians. Thus, the number of years of shiftwork until the diagnosis of the first reduction in fitness for duty could be calculated. Survival analyses were performed to estimate the risk (hazard rate) for experiencing a reduction in fitness for duty across lifetime exposure to shiftwork in years, controlling for age, sex, work type, and police district. Hazard estimates were compared across both samples to cross-validate the results. The findings indicated an increase in the risk of reduced fitness for duty with increasing number of years in shiftwork during the working life in both samples. The hazard rates followed an exponential trend, indicating a rapid increase in health impairments in particular beyond 20 yrs of shiftwork. These findings were consistent in both samples, collected with different methods and over different time periods, thus indicating high validity. Therefore, occupational stress factors, such as exposure to shiftwork, need to be taken into account when discussing the postponement of the legal retirement age.

Adrenergic nerves govern circadian leukocyte recruitment to tissues

The multistep sequence leading to leukocyte migration is thought to be locally regulated at the inflammatory site. Here, we show that broad systemic programs involving long-range signals from the sympathetic nervous system (SNS) delivered by adrenergic nerves regulate rhythmic recruitment of leukocytes in tissues. Constitutive leukocyte adhesion and migration in murine bone marrow (BM) and skeletal-muscle microvasculature fluctuated with circadian peak values at night. Migratory oscillations, altered by experimental jet lag, were implemented by perivascular SNS fibers acting on β-adrenoreceptors expressed on nonhematopoietic cells and leading to tissue-specific, differential circadian oscillations in the expression of endothelial cell adhesion molecules and chemokines. We showed that these rhythms have physiological consequences through alteration of hematopoietic cell recruitment and overall survival in models of septic shock, sickle cell vaso-occlusion, and BM transplantation. These data provide unique insights in the leukocyte adhesion cascade and the potential for time-based therapeutics for transplantation and inflammatory diseases.

Shift work and vascular events: systematic review and meta-analysis

OBJECTIVE

To synthesise the association of shift work with major vascular events as reported in the literature.

DATA SOURCES

Systematic searches of major bibliographic databases, contact with experts in the field, and review of reference lists of primary articles, review papers, and guidelines.

STUDY SELECTION

Observational studies that reported risk ratios for vascular morbidity, vascular mortality, or all cause mortality in relation to shift work were included; control groups could be non-shift ("day") workers or the general population.

DATA EXTRACTION

Study quality was assessed with the Downs and Black scale for observational studies. The three primary outcomes were myocardial infarction, ischaemic stroke, and any coronary event. Heterogeneity was measured with the I(2) statistic and computed random effects models.

RESULTS

34 studies in 2,011,935 people were identified. Shift work was associated with myocardial infarction (risk ratio 1.23, 95% confidence interval 1.15 to 1.31; I(2)=0) and ischaemic stroke (1.05, 1.01 to 1.09; I(2)=0). Coronary events were also increased (risk ratio 1.24, 1.10 to 1.39), albeit with significant heterogeneity across studies (I(2)=85%). Pooled risk ratios were significant for both unadjusted analyses and analyses adjusted for risk factors. All shift work schedules with the exception of evening shifts were associated with a statistically higher risk of coronary events. Shift work was not associated with increased rates of mortality (whether vascular cause specific or overall). Presence or absence of adjustment for smoking and socioeconomic status was not a source of heterogeneity in the primary studies. 6598 myocardial infarctions, 17,359 coronary events, and 1854 ischaemic strokes occurred. On the basis of the Canadian prevalence of shift work of 32.8%, the population attributable risks related to shift work were 7.0% for myocardial infarction, 7.3% for all coronary events, and 1.6% for ischaemic stroke.

CONCLUSIONS

Shift work is associated with vascular events, which may have implications for public policy and occupational medicine.

Daytime sleepiness and risk of stroke and vascular disease: findings from the Northern Manhattan Study (NOMAS)

BACKGROUND

Recent studies have suggested that poor quality and diminished quantity of sleep may be independently linked to vascular events although prospective and multiethnic studies are limited. This study aimed to explore the relationship between daytime sleepiness and the risk of ischemic stroke and vascular events in an elderly, multiethnic prospective cohort.

METHODS AND RESULTS

As part of the Northern Manhattan Study, the Epworth Sleepiness Scale was collected during the 2004 annual follow-up. Daytime sleepiness was trichotomized using previously reported cut points of no dozing, some dozing, and significant dozing. Subjects were followed annually for a mean of 5.1 years. Cox proportional hazards models were used to calculate hazard ratios and 95% confidence intervals for stroke, myocardial infarction, and death outcomes. We obtained the Epworth Sleepiness Scale on 2088 community residents. The mean age was 73.5 ± 9.3 years; 64% were women; 17% were white, 20% black, 60% Hispanic, and 3% were other. Over 44% of the cohort reported no daytime dozing, 47% some dozing, and 9% significant daytime dozing. Compared with those reporting no daytime dozing, individuals reporting significant dozing had an increased risk of ischemic stroke (hazard ratio, 2.74 [95% confidence interval, 1.38-5.43]), all stroke (3.00 [1.57-5.73]), the combination of ischemic stroke, myocardial infarction, and vascular death (2.38 [1.50-3.78]), and all vascular events (2.48 [1.57-3.91]), after adjusting for medical comorbidities.

CONCLUSIONS

Daytime sleepiness is an independent risk factor for stroke and other vascular events. These findings suggest the importance of screening for sleep problems at the primary care level.

Shift work and the assessment and management of shift work disorder (SWD)

Nearly 20% of the labor force worldwide, work shifts that include work hours outside 07:00 h to 18:00 h. Shift work is common in many occupations that directly affect the health and safety of others (e.g., protective services, transportation, healthcare), whereas quality of life, health, and safety during shift work and the commute home can affect workers in any field. Increasing evidence indicates that shift-work schedules negatively influence worker physiology, health, and safety. Shift work disrupts circadian sleep and alerting cycles, resulting in disturbed daytime sleep and excessive sleepiness during the work shift. Moreover, shift workers are at risk for shift work disorder (SWD). This review focuses on shift work and the assessment and management of sleepiness and sleep disruption associated with shift work schedules and SWD. Management strategies include approaches to promote sleep, wakefulness, and adaptation of the circadian clock to the imposed work schedule. Additional studies are needed to further our understanding of the mechanisms underlying the health risks of shift work, understanding which shift workers are at most risk of SWD, to investigate treatment options that address the health and safety burdens associated with shift work and SWD, and to further develop and assess the comparative effectiveness of countermeasures and treatment options.

Sleep disorders and stroke

The purpose of this review is to highlight existing literature on the epidemiology, pathophysiology, and treatments of stroke sleep disorders. Stroke sleep disorders are associated with many intermediary vascular risk factors leading to stroke, but they may also influence these risk factors through direct or indirect mechanisms. Sleep disturbances may be further exacerbated by stroke or caused by stroke. Unrecognized and untreated sleep disorders may influence rehabilitation efforts and poor functional outcomes following stroke and increase risk for stroke recurrence. Increasing awareness and improving screening for sleep disorders is paramount in the primary and secondary prevention of stroke and in improving stroke outcomes. Many vital questions about the relationship of sleep disorders and stroke are still unanswered and await future well-designed studies.

Night shift work and hormone levels in women

BACKGROUND

Night shift work may disrupt the normal nocturnal rise in melatonin, resulting in increased breast cancer risk, possibly through increased reproductive hormone levels. We investigated whether night shift work is associated with decreased levels of urinary 6-sulfatoxymelatonin, the primary metabolite of melatonin, and increased urinary reproductive hormone levels.

METHODS

Participants were 172 night shift and 151 day shift-working nurses, aged 20-49 years, with regular menstrual cycles. Urine samples were collected throughout work and sleep periods and assayed for 6-sulfatoxymelatonin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estrone conjugate (E1C).

RESULTS

6-Sulfatoxymelatonin levels were 62% lower and FSH and LH were 62% and 58% higher, respectively, in night shift-working women during daytime sleep than in day shift-working women during nighttime sleep (P ≤ 0.0001). Nighttime sleep on off-nights was associated with 42% lower 6-sulfatoxymelatonin levels among the night shift workers, relative to the day shift workers (P < 0.0001); no significant differences in LH or FSH were observed. 6-Sulfatoxymelatonin levels during night work were approximately 69% lower and FSH and LH were 35% and 38% higher, compared with day shift workers during nighttime sleep. No differences in E1C levels between night and day shift workers were observed. Within night shift workers, 6-sulfatoxymelatonin levels were lower and reproductive hormone levels were higher during daytime sleep and nighttime work, relative to nighttime sleep (P < 0.05).

CONCLUSIONS

These results indicate that night shift workers have substantially reduced 6-sulfatoxymelatonin levels during night work and daytime sleep and that levels remain low even when a night shift worker sleeps at night.

IMPACT

Shift work could be an important risk factor for many other cancers in addition to breast cancer.

Rotating night shift work and disparate hypertension risk in African-Americans

OBJECTIVE

Hypertension disproportionally affects black compared with white Americans, even after accounting for known risk factors. Circadian disruption as encountered by rotating night shift workers has been associated with an increased risk for hypertension. Because blood pressure responds differently to sleep alterations in blacks compared with whites, we hypothesized that rotating night shift work may be a stronger risk factor for hypertension among blacks.

METHODS

We prospectively examined the association between rotating night shift work and the risk of hypertension in 1510 black and 94 142 white female participants of the Nurses' Health Study II who were nonhypertensive at baseline in 1991. We used Cox proportional hazards models to control for potential confounders.

RESULTS

During 16 years of follow-up (1991-2007), we identified 580 incident cases of hypertension in blacks and 23 360 cases in whites. In blacks, the multivariable hazard ratio for incident hypertension among women who worked rotating night shift for more than 12 months in the previous 2 years was 1.81 [95% confidence interval (CI) 1.14-2.87], compared with those working none. By contrast, in whites, we observed no increase in risk (hazard ratio 0.99, 95% CI 0.93-1.06). The association between shift work and hypertension varied significantly by race (P interaction = 0.01). In secondary analyses, the multivariable hazard ratio for incident hypertension in black women who ever performed rotating night shift work was 1.46 (95% CI 1.07-1.99), compared with those never working rotating night shifts. In whites, there was no increase in risk (hazard ratio 0.97, 95% CI 0.93-1.01) (P interaction < 0.01).

CONCLUSION

Rotating night shift work is independently associated with an increased risk of hypertension in blacks but not in whites.

Is shift work making your patient sick? Emerging theories and therapies for treating shift work disorder

"Shift work" is a term that applies to a wide array of nontraditional work schedules. Shift work disorder (SWD) is a circadian rhythm sleep disorder experienced by a subset of shift workers that is characterized by excessive sleepiness during work and/or insomnia during scheduled sleep times. It is estimated to affect up to 2 million Americans, and is associated with increased morbidity and mortality from metabolic risk factors, cardiovascular and gastrointestinal diseases, depression, accidents, and some kinds of cancers. Patient history is all that is needed to make a diagnosis with the International Classification of Sleep Disorders-Second Edition criteria as described herein. Circadian rhythm disorders, in which an underlying misalignment of circadian rhythm with the sleep-wake cycle occurs, may be treated by behavioral and pharmacologic approaches, including the use of hypnotics to improve the duration of sleep. However, evidence is limited with these approaches in patients diagnosed with SWD. Other treatment options may include pharmacologic interventions such as modafinil and armodafinil, which have shown efficacy in this population. Combined therapy can reduce insomnia and excessive sleepiness, and improve attention and alertness during work shifts and the subsequent commute home.

Self-reported sleep duration and prediction of proteinuria: a retrospective cohort study

BACKGROUND

Although multiple studies have shown that sleep duration is a predictor of cardiovascular diseases and mortality, few studies have reported an association between sleep duration and chronic kidney disease.

STUDY DESIGN

Retrospective cohort study.

SETTING & PARTICIPANTS

6,834 employees of Osaka University aged 20-65 years who visited Osaka University Healthcare Center for their mandatory annual health examinations between April 2006 and March 2010 and did not have estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2), proteinuria, or treatment for self-reported kidney disease.

PREDICTOR

Self-reported questionnaires about life style, including sleep duration, and blood and urine testing at the first examinations during the study period. An association between sleep duration and outcome was assessed using multivariate Poisson regression models adjusting for clinically relevant factors.

OUTCOME

Time to the development of proteinuria defined as 1+ or higher by dipstick test.

RESULTS

Self-reported baseline sleep duration was 6.0 ± 0.9 hours, which reflected the mean sleep duration during a median of 2.5 (25th-75th percentile, 1.4-3.9) years of the observational period. Development of proteinuria was observed in 550 employees (8.0%). A multivariate Poisson regression model clarified that shorter sleep duration, especially 5 or fewer hours, was associated with the development of proteinuria in a stepwise fashion (vs 7 hours; incidence rate ratios of 1.07 [95% CI, 0.87-1.33; P = 0.5], 1.28 [95% CI, 1.00-1.62; P = 0.05], and 1.72 [95% CI, 1.16-2.53; P = 0.007] for 6, 5, and ≤4 hours, respectively), along with younger age, heavier current smoking, trace urinary protein by dipstick test, higher eGFR, higher serum hemoglobin A(1c) level, and current treatment for heart disease. A stepwise association between shorter sleep duration and the development of proteinuria also was verified in 4,061 employees who did not work the night shift.

LIMITATIONS

Self-reported sleep duration might be biased. Results in a single center should be confirmed in the larger cohort including different occupations.

CONCLUSION

Short sleep duration, especially 5 or fewer hours, was a predictor of proteinuria.

Sunlight exposure, vitamin D, and risk of non-Hodgkin lymphoma in the Nurses' Health Study

PURPOSE

Case-control studies suggest increased sun exposure reduces non-Hodgkin lymphoma (NHL) risk. Evidence from prospective cohort studies, however, is limited and inconsistent. We evaluated the association between ambient ultraviolet radiation (UV) exposure and NHL in a nationwide cohort of women, the Nurses' Health Study (NHS).

METHODS

Between 1976 and 2006, we identified 1064 incident NHL cases among 115,482 women in the prospective NHS. Exposures assessed included average annual UV-B flux based on residence at various times during life, vitamin D intake, and predicted plasma 25-hydroxyvitamin D levels. We estimated incidence rate ratios (RRs) and 95% confidence intervals (CIs) for risk of all NHL and histologic subtypes using Cox proportional hazards models.

RESULTS

NHL risk was increased for women residing in areas of high ambient UV radiation (UV-B flux >113 R-B count × 10(-4)) compared to those with lower exposure (<113), with positive linear trends at all time points. The multivariable-adjusted RR for high UV area at age 15 was 1.21 (95% CI: 1.00, 1.47; p-trend < 0.01). There was no evidence of statistical heterogeneity by subtype, although power was limited for subtype analyses. We observed no association between vitamin D measures and risk of NHL overall or by subtype.

CONCLUSIONS

Our findings do not support the hypothesis of a protective effect of UV radiation exposure on NHL risk. We found no association between vitamin D and NHL risk.

Shift work and chronic disease: the epidemiological evidence

BACKGROUND

Shift work, including night work, has been hypothesized to increase the risk of chronic diseases, including cancer, cardiovascular disease (CVD), metabolic syndrome and diabetes. Recent reviews of evidence relating to these hypotheses have focussed on specific diseases or potential mechanisms, but no general summary of the current data on shift work and chronic disease has been published.

METHODS

Systematic and critical reviews and recent original studies indexed in PubMed prior to 31 December 2009 were retrieved, aided by manual searches of reference lists. The main conclusions from reviews and principle results from recent studies are presented in text and tables.

RESULTS

Published evidence is suggestive but not conclusive for an adverse association between night work and breast cancer but limited and inconsistent for cancers at other sites and all cancers combined. Findings on shift work, in relation to risks of CVD, metabolic syndrome and diabetes are also suggestive but not conclusive for an adverse relationship.

CONCLUSIONS

Heterogeneity of study exposures and outcomes and emphasis on positive but non-significant results make it difficult to draw general conclusions. Further data are needed for additional disease endpoints and study populations.

Work-related cerebro-cardiovascular diseases in Korea

Cerebro-cardiovascular disease (CVD) is one of compensable occupational diseases in Korea as in Japan or Taiwan. However, most countries accept only cardiovascular diseases (ischemic heart diseases) as compensable occupational diseases if any, but not cerebrovascular diseases. Korea has a prescribed list of compensable occupational diseases. CVD was not included in the list until 1993. In the early 1990s, a case of cerebral infarction was accepted as occupational disease by the Supreme Court. The decision was based on the concept that workers' compensation system is one of the social security systems. In 1994, the government has established a diagnostic criterion of CVD. The crude rate of compensated cerebrovascular disease decreased by 60.0% from 18.5 in 2003 to 7.4 in 2008 per 100,000 workers, and that of compensated coronary heart disease decreased by 60.5% from 3.8 in 2003 to 1.5 in 2008 per 100,000 workers. The compensated cases of CVD dramatically increased and reached its peak in 2003. Since many preventive activities were performed by the government and employers, the compensated cases have slowly decreased since 2003 and sharply decreased after 2008 when the diagnostic criterion was amended. The strategic approach is needed essentially because CVDs are common, serious and preventable diseases which lead to economic burden.

Circadian regulation of cardiovascular function: a role for vasoactive intestinal peptide

The circadian system, driven by the suprachiasmatic nucleus (SCN), regulates properties of cardiovascular function. The dysfunction of this timing system can result in cardiac pathology. The neuropeptide vasoactive intestinal peptide (VIP) is crucial for circadian rhythms in a number of biological processes including SCN electrical activity and wheel running behavior. Anatomic evidence indicates that SCN neurons expressing VIP are well positioned to drive circadian regulation of cardiac function through interactions with the autonomic centers. In this study, we tested the hypothesis that loss of VIP would result in circadian deficits in heart rate (HR) and clock gene expression in cardiac tissue. We implanted radiotelemetry devices into VIP-deficient mice and wild-type (WT) controls and continuously recorded HR, body temperature, and cage activity in freely moving mice. Under light-dark conditions, VIP-deficient mice displayed weak rhythms in HR, body temperature, and cage activity, with onsets that were advanced in phase compared with WT mice. Similarly, clock gene expression in cardiac tissue was rhythmic but phase advanced in mutant mice. In constant darkness, the normal circadian rhythms in HR were lost in VIP-deficient mice; however, most mutant mice continued to exhibit circadian rhythms of body temperature with shortened free-running period. The loss of VIP altered, but did not abolish, autonomic regulation of HR. Analysis of the echocardiograms did not find any evidence for a loss of cardiac function in VIP-deficient mice, and the size of the hearts did not differ between genotypes. These results demonstrate that VIP is an important regulator of physiological circadian rhythmicity in the heart.

A cross-sectional study on the shift work and metabolic syndrome in Japanese male workers

INTRODUCTION

Shift work has been reported to be associated with an increase in the metabolic syndrome (MetS). To clarify the association between the type of shift work and the risk of MetS, a cross-sectional field survey was conducted after adjusting for age and lifestyle factors.

METHODS

The subjects were 3007 Japanese males, aged 34-64 years old, who were employees (1700 day and 1307 shift workers) of a car-manufacturing company. The standard Japanese criteria for the diagnosis of MetS was used. Age, smoking habit, drinking habit, sleeping habit and exercise habit were used as the independent variables.

RESULTS

The prevalence of MetS in the day workers, two-shift workers, and three-shift workers were 13.8% (234/1700), 10.7% (120/1125) and 17.6% (32/182), respectively. There was a significant difference in the prevalence between the two-shift workers and the day workers. Estimation of the odds ratios (95% confidence intervals) of age, two-shift work and habitual exercise for MetS were 1.03 (1.01-1.04), 0.77 (0.61-0.98) and 0.64 (0.51-0.81), respectively.

CONCLUSION

Two-shift work was associated with lower risk of MetS, which is not in accordance with past reports. This finding should therefore be re-analysed, including investigation of the job content in each group.

Healthy clocks, healthy body, healthy mind

Circadian rhythms permeate mammalian biology. They are manifested in the temporal organisation of behavioural, physiological, cellular and neuronal processes. Whereas it has been shown recently that these approximately 24-hour cycles are intrinsic to the cell and persist in vitro, internal synchrony in mammals is largely governed by the hypothalamic suprachiasmatic nuclei that facilitate anticipation of, and adaptation to, the solar cycle. Our timekeeping mechanism is deeply embedded in cell function and is modelled as a network of transcriptional and/or post-translational feedback loops. Concurrent with this, we are beginning to understand how this ancient timekeeper interacts with myriad cell systems, including signal transduction cascades and the cell cycle, and thus impacts on disease. An exemplary area where this knowledge is rapidly expanding and contributing to novel therapies is cancer, where the Period genes have been identified as tumour suppressors. In more complex disorders, where aetiology remains controversial, interactions with the clockwork are only now starting to be appreciated.