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

OBJECTIVE: With workforces in industrialized countries getting older, the study examined how shiftworking affects sleep in later life. METHOD: Longitudinal data were collected in 1996, 2001, and 2006 from a large sample of employees who were 32, 42, 52, and 62 years old in 1996. RESULTS: Effects of shiftwork were most apparent in middle-aged participants, becoming less apparent in later years when people tended to leave shiftwork. Nevertheless, a group of younger former shiftworkers reported more sleep problems than those who had never worked shifts. Giving up shiftwork offset a trend for sleep problems to accumulate over time, with the net result of no change in sleep problems after cessation of shiftwork. CONCLUSIONS: Poor sleep quality is a temporary consequence of shiftwork for some, whereas for others it is a cause of shiftwork intolerance.

Effects of working conditions and sleep of the previous day on cognitive performance.

The study examined the consequences of working conditions on the previous day on cognitive performance the following day. It also addressed the issue of whether this relationship was mediated by sleep and whether it differed as a function of age. The data were taken from the VISAT study (aging, health and work) and concerned the participant's general work schedule, general sleep quality, working conditions on the previous day (content, duration, load and schedule), subsequent sleep length and quality, and cognitive performance. Results showed that both physical activity and working before 6 am or after 10 pm on the previous day were significantly associated with poorer cognitive performance. Significant effects of working conditions on the previous day were also observed on subsequent sleep, but these effects did not mediate the relationship between working conditions and cognitive performance. The observed effect on cognitive performance of atypical work hours on the previous day was similar for all ages, probably because of the healthy worker effect.

Relation between body mass index and cognitive function in healthy middle-aged men and women.

OBJECTIVE: To assess whether body mass index (BMI) is associated with cognitive function and cognitive decline in healthy men and women. METHODS: In this prospective cohort study, we analyzed data from 2,223 healthy workers aged 32 to 62 years at baseline. Medical, psychosocial, and environmental data were collected in 1996 and in 2001. We tested cognitive functions at baseline and at follow-up with word-list learning (four recalls), a Digit-Symbol Substitution Test, and a selective attention test. RESULTS: Cross-sectionally, a higher BMI was associated with lower cognitive scores after adjustment for age, sex, educational level, blood pressure, diabetes, and other psychosocial covariables. A higher BMI at baseline was also associated with a higher cognitive decline at follow-up, after adjustment for the above-cited confounding factors. This association was significant for word-list learning. For the changes in scores at word-list learning (delayed recall), regression coefficients were -0.008 +/- 0.13, -0.09 +/- 0.13, -0.17 +/- 0.14, and -0.35 +/- 0.14 (p for trend < 0.001) for the second, third, fourth, and fifth quintiles of BMI at baseline when compared with the first quintile. No significant association was found between changes in BMI and cognitive function. CONCLUSIONS: Body mass index was independently associated both with cognitive function (word-list learning and Digit-Symbol Substitution Test) and changes in word-list learning in healthy, nondemented, middle-aged men and women.