Chronic effects of shift work on cognition: findings from the VISAT longitudinal study.

OBJECTIVES: Shift work, like chronic jet lag, is known to disrupt workers' normal circadian rhythms and social life, and to be associated with increased health problems (eg, ulcers, cardiovascular disease, metabolic syndrome, breast cancer, reproductive difficulties) and with acute effects on safety and productivity. However, very little is known about the long-term consequences of shift work on cognitive abilities. The aim of this study was to assess the chronicity and reversibility of the effects of shift work on cognition. METHODS: We conducted a prospective cohort study of 3232 employed and retired workers (participation rate: 76%) who were 32, 42, 52 and 62 years old at the time of the first measurement (t1, 1996), and who were seen again 5 (t2) and 10 (t3) years later. 1484 of them had shift work experience at baseline (current or past) and 1635 had not. The main outcome measures were tests of speed and memory, assessed at all three measurement times. RESULTS: Shift work was associated with impaired cognition. The association was stronger for exposure durations exceeding 10 years (dose effect; cognitive loss equivalent to 6.5 years of age-related decline in the current cohort). The recovery of cognitive functioning after having left shift work took at least 5 years (reversibility). CONCLUSIONS: Shift work chronically impairs cognition, with potentially important safety consequences not only for the individuals concerned, but also for society.

Effects of age, gender, and retirement on perceived sleep problems: results from the VISAT combined longitudinal and cross-sectional study.

OBJECTIVES: This study examined the effects of age, gender, and retirement on the subjective frequency of various sleep problems in individuals on a normal work schedule. DESIGN: Data were taken from the VISAT study (Aging, Health, - Work), which allowed both cross-sectional and longitudinal aspects of age-related changes to be examined. SETTING: Various sorts of companies in southern France. PARTICIPANTS: The cohorts comprised 623 male and female, employed and retired, wage earners who were 32, 42, 52, and 62 years old at the time of the first measurement (t1, 1996), and who were seen again 5 (t2) and 10 (t3) years later. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: Subjective ratings of the frequency of sleep problems and hypnotic usage were recorded on all 3 occasions, as was the employment status of the individuals. After controlling for age and gender, an effect of decade was observed for difficulty falling asleep and difficulty maintaining sleep, indicating that the frequency of these sleep problems was rated higher in 2006 than in 1996 by people of the same age at both measurement occasions. The perceived frequency of difficulty maintaining sleep, difficulty getting back to sleep, and premature awakening was found to increase up to the mid-50s but to then remain relatively constant, or even in the case of premature awakening to reduce, up to the age of 72. There was also a significant improvement in premature awakening among those individuals who changed from being active to being retired during the study period (n = 111). In contrast, the rated frequency of difficulty falling asleep and hypnotic usage increased fairly linearly over the entire age range. CONCLUSIONS: Sleep complaints were reported early in the workers' lives, and were more frequent with age, but some of them improved after retirement, especially the complaint of premature awakening.

Shiftwork and metabolic dysfunction.

Many of the health problems that are more prevalent among shiftworkers are thought to be linked to their heightened susceptibility to metabolic syndrome, i.e., the association of even moderate degrees of visceral obesity, dyslipidemia, abnormal blood pressure, and serum glucose levels in the same individual. Although previous studies have identified associations between shiftwork and metabolic syndrome, there is relatively little evidence to date of how the risk of developing it varies as a function of exposure to shiftwork. The current study seeks to confirm earlier findings of an association between shiftwork exposure and metabolic dysfunction, and to examine the impact of exposure duration, while adjusting for a number of covariates in the analyses. The analyses were based on data from VISAT, a study involving the measurement of physiological, behavioral, and subjective outcomes from 1757 participants, 989 being current or former shiftworkers. The sample comprised employed and retired wage earners, male and female, who were 32, 42, 52, and 62 yrs old. The first analysis sought to confirm previous findings of an association between exposure to shiftwork and the risk of developing metabolic syndrome. It indicated that participants who were or who had previously been shiftworkers (i.e., working schedules that involved rotating shifts; not being able to go to bed before midnight; having to get up before 05:00 h; or being prevented from sleeping during the night) were more likely to exhibit symptoms of metabolic syndrome, after adjusting for age, sex, socioeconomic status, smoking, alcohol intake, perceived stress, and sleep difficulty (odds ratio [OR] 1.78; 95% confidence interval [CI] 1.03-3.08). The results suggest the association between shiftwork and metabolic syndrome cannot be fully accounted for by either higher levels of strain or increased sleep difficulty among shiftworkers, although it remains a possibility that either one or both of these factors may have played a contributing role. The second analysis addressed the issue of duration of exposure to shiftwork. Participants with >10 yrs' experience of working rotating shifts were more likely to exhibit symptoms of metabolic syndrome than participants without exposure to shiftwork, i.e., dayworkers, even after adjusting for age and sex (OR 1.96; 95% CI 1.03-3.75). Thus, the current study confirms the association between shiftwork exposure and metabolic syndrome. It also provides new information regarding the time course of the development of the illness as function of exposure duration, although this was only examined in relation to rotating shiftwork. It is concluded that those responsible for monitoring workers' health should pay particular attention to indices of metabolic dysfunction in workers who have been exposed to shiftwork for >10 yrs.

Impact of long-term benzodiazepine use on cognitive functioning in young adults: the VISAT cohort.

PURPOSE: Results from a number of studies have suggested a relationship between cognitive alteration and benzodiazepine use in the elderly. The aim of this study was to determine the impact of benzodiazepine use on cognitive functions in a young adult population. METHODS: This study included 1,019 French salaried workers from the VISAT (Aging, Health and Work) cohort whose objective was to determine the long-term impact of working conditions on health and aging. Data were collected during interviews by occupational physicians in 1996, 2001 and 2006. Cognitive function was assessed using five cognitive tests (immediate free recall test, delayed free recall test, recognition test, Digit Symbol Substitution Subtest and visual search speed test). Cognitive scores obtained after a 10-year follow-up were investigated among three categories of benzodiazepine users, namely, non-users, occasional users and long-term users, using analysis of covariance models adjusted for several potential confounders in men and women separately. RESULTS: In the course of the 10 year-follow-up, 3.9% of subjects were defined as occasional users of benzodiazepine and 7.5% as long-term users. The analysis revealed a significant alteration of long-term memory in women whereas there was no significant association in men. CONCLUSIONS: Long-term use of benzodiazepine leads to specific impairment in long-term memory only in women.

The effects of age and shiftwork on perceived sleep problems: results from the VISAT-combined longitudinal and cross-sectional study.

OBJECTIVES: With the workforces in industrialized countries getting older, this study sought to determine how shiftworking affects sleep in later life. METHOD: Longitudinal data were collected from a large sample in 1996, 2001, and 2006 from employees who were 32, 42, 52, and 62 years old in 1996. RESULTS: The effects of shift work were most apparent in the early and middle years of working life. Former shiftworkers reported more sleep problems than both current shiftworkers and those who had never worked shifts. Giving up shift work off-set the age-related accumulation of sleep problems, with the net result that former shiftworkers showed little or no change in sleep problems over the three measurement occasions. CONCLUSIONS: The effects of shift work on sleep may persist for a long time after giving up shift work but they are not permanent.

Shiftwork experience, age and cognitive performance.

Changes of alertness and cognitive efficiency has been suggested in people whose circadian rhythms are disrupted, e.g. night or shift-workers. Data from field and laboratory studies have demonstrated short-term cognitive disturbances related to circadian rhythm disruption. By contrast, little is known about the long-term consequences of chronic sleep deprivation, as can be observed with shift-work, on cognitive abilities. The present paper is aimed at evaluating, on a large cross-sectional sample of workers, the long-term influence of shift-work on verbal memory and speed performances. Participants were 3,237 workers aged 32, 42, 52, and 62 years of various occupational statuses included in the VISAT (Aging, Health and Work) cohort. Data collected by questionnaires included items on working hours and shift-work and sleep disorders. Cognitive abilities were assessed using neuropsychological tests. Current male shift-workers had lower cognitive performance than never exposed workers. In the same population, memory performance tended to decrease with increasing shift-work duration. Among former shift-workers, the cognitive performance of the participant having stopped shiftwork more than 4 years ago seemed to be increased, suggesting a possible reversibility of effects. In conclusion, this study demonstrated that cognitive functioning tends to be impaired by a long-term exposure to SW. As found by other authors, neuropsychological performance tends to decrease with the increases in the duration of exposure to SW.