Puttonen S, Härmä M, Hublin C. Shift work and cardiovascular disease -pathways from circadian stress to morbidity. Scand J Work Environ Health. 2010;36(2):96-108.In order to establish a causal relation between shift work and cardiovascular disease (CVD), we need to verify the pathways from the former to the latter. This paper aims to review the current knowledge of the mechanisms between shift work and CVD. Shift work can increase the risk of CVD by several interrelated psychosocial, behavioral, and physiological mechanisms. The psychosocial mechanisms relate to difficulties in controlling working hours, decreased work-life balance, and poor recovery following work. The most probable behavioral changes are weight gain and smoking. The plausible physiological and biological mechanisms are related to the activation of the autonomic nervous system, inflammation, changed lipid and glucose metabolism, and related changes in the risk for atherosclerosis, metabolic syndrome, and type II diabetes. The data provide evidence for possible disease mechanisms between shift work and CVD, but compelling evidence on any specific mechanism is missing.

BackgroundSleep restriction, leading to deprivation of sleep, is common in modern 24-h societies and is associated with the development of health problems including cardiovascular diseases. Our objective was to investigate the immunological effects of prolonged sleep restriction and subsequent recovery sleep, by simulating a working week and following recovery weekend in a laboratory environment.Methods and FindingsAfter 2 baseline nights of 8 hours time in bed (TIB), 13 healthy young men had only 4 hours TIB per night for 5 nights, followed by 2 recovery nights with 8 hours TIB. 6 control subjects had 8 hours TIB per night throughout the experiment. Heart rate, blood pressure, salivary cortisol and serum C-reactive protein (CRP) were measured after the baseline (BL), sleep restriction (SR) and recovery (REC) period. Peripheral blood mononuclear cells (PBMC) were collected at these time points, counted and stimulated with PHA. Cell proliferation was analyzed by thymidine incorporation and cytokine production by ELISA and RT-PCR. CRP was increased after SR (145% of BL; p<0.05), and continued to increase after REC (231% of BL; p<0.05). Heart rate was increased after REC (108% of BL; p<0.05). The amount of circulating NK-cells decreased (65% of BL; p<0.005) and the amount of B-cells increased (121% of BL; p<0.005) after SR, but these cell numbers recovered almost completely during REC. Proliferation of stimulated PBMC increased after SR (233% of BL; p<0.05), accompanied by increased production of IL-1β (137% of BL; p<0.05), IL-6 (163% of BL; p<0.05) and IL-17 (138% of BL; p<0.05) at mRNA level. After REC, IL-17 was still increased at the protein level (119% of BL; p<0.05).Conclusions5 nights of sleep restriction increased lymphocyte activation and the production of proinflammatory cytokines including IL-1β IL-6 and IL-17; they remained elevated after 2 nights of recovery sleep, accompanied by increased heart rate and serum CRP, 2 important risk factors for cardiovascular diseases. Therefore, long-term sleep restriction may lead to persistent changes in the immune system and the increased production of IL-17 together with CRP may increase the risk of developing cardiovascular diseases.

This paper aims at describing the associations between workhours and psychosocial work characteristics and reviews the health effects of workhours and the related pathways. The role of insufficient sleep as a possible common pathway from workhours and work stress to cardiovascular illness is discussed. Finally, the key possibilities for improving recovery and health through changes in workhours are identified. Night work and shift work are related to a wide range of health effects, the evidence for the risk of cardiovascular morbidity being the strongest. Insufficient or poor sleep, related to insufficient recovery, can be a common pathway from long workhours, shift work, and work stress to cardiovascular illness. The most promising worktime-related means for decreasing the psychosocial workload and negative health effects of workhours would be (i) to regulate overtime and excessive workhours, (ii) increase individual worktime control, and (iii) increase recovery from the introduction of sleep-promoting principles into shift rotation.

SUMMARY A hypothesis concerning habitual sleep reduction and its adverse consequences among general population in modern societies has received wide publicity in the mass media, although scientific evidence supporting the hypothesis is scarce. Similarly, there is an extensively distributed belief, at least in Finland, that the prevalence of insomniarelated symptoms is increasing, but evidence for this is even sparser. These issues are important because of the known increased risk of mortality and health risks associated with sleep duration deviating from 7 to 8 h. To reveal possible trends in self-reported sleep duration and insomnia-related symptoms, we reanalyzed all available data from surveys carried out in Finland from 1972 to 2005. The main results were that a minor decrease of self-reported sleep duration has taken place in Finland, especially among working aged men. However, the size of the reduction (about 4%) was relatively small, approximately 5.5 min per each 10 years during the 33 yearsÕ time interval under study. The proportion of 7 h sleepers has increased and, correspondingly, the proportion of 8 h sleepers has decreased, but the extreme ends of the sleep duration distribution remained unchanged. Tentative evidence suggesting an increase in insomnia-related symptoms among working aged population during the last 10 years was found. In conclusion, the Finnish data during the past 33 years indicate a general decrease in selfreported sleep duration of about 18 min and an increase of sleep complaints, especially among the employed middle-aged population.

SUMMARY Self-reported short or long sleep duration has been repeatedly found to be associated with increased mortality and health risks. However, there is still an insufficient amount of detailed knowledge available to characterize the short and long sleep duration groups in general population. Consequently, the underlying mechanisms potentially explaining the health risks associated with short and long sleep duration are unclear. In the present study, the self-reported sleep duration in a sample of Finnish general population was studied, and its possible associations with such factors as self-perceived health, sociodemographic characteristics, lifestyle, sleep difficulties and daytime concomitants were analyzed. In particular, an effort was made to define mutually statisticallyindependent determinants of sleep duration. In the Finnish Health 2000 Survey, a representative sample of 8028 subjects of 30 years of age or older and a sample of 1894 subjects of 18-29 years of age were invited to take part in the health interview and health examination. The participation rate of the study was over 80%. The most important and statistically-independent determinants of short and long sleep duration were gender, physical tiredness, sleep problems, marital status, main occupation and physical activity. However, in the multivariable model they only accounted for approximately 16% of the variance in sleep duration in short and long sleepers, suggesting multiple sources of variance. The present study also suggests a dose-response like relationship between the sleep duration and many of its determinants within both short and long sleepers. A more detailed analysis of the clinical status of the short and long sleep duration groups is needed to evaluate the possible importance of these findings for health risks associated with sleep duration.k e y w o r d s epidemiology, long sleepers, representative sample, short sleepers, sleep duration, sleep length

The developed method and algorithms allow a detailed characterization of four main dimensions of working time patterns potentially relevant for health. We recommend this method for future large-scale epidemiological studies.

The use of a short (< 1 h) nap in improving alertness during the early morning hours in the first night shift was examined under laboratory conditions. The study contained four experimental, non‐consecutive night shifts with a nap of either 50 or 30 min at 01.00 or 04.00 hours. An experimental night shift without a nap served as a control condition. Each experimental shift was followed by daytime sleep. Fourteen experienced male shift workers went through all of the experimental conditions. The results showed that the naps improved the ability to respond to visual signals during the second half of the night shift. Physiological sleepiness was alleviated by the early naps, as measured 50 min after awakening, but not at the end of the shift. Subjective sleepiness was somewhat decreased by the naps. The naps produced sleep inertia which lasted for about 10–15 min. Daytime sleep was somewhat impaired by the 50 min naps. The study shows that a nap shorter than 1 h is able to improve alertness to a certain extent during the first night shift.

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