Shift work and risk of incident dementia: a study of two population-based cohorts.

This study aimed to investigate the association between shift work and incident dementia in two population-based cohorts from the Swedish Twin Registry (STR). The STR-1973 sample included 13,283 participants born 1926-1943 who received a mailed questionnaire in 1973 that asked about status (ever/never) and duration (years) of shift work employment. The Screening Across the Lifespan Twin (SALT) sample included 41,199 participants born 1900-1958 who participated in a telephone interview in 1998-2002 that asked about night work status and duration. Dementia diagnoses came from Swedish patient registers. Cox proportional-hazards regression was used to estimate hazard ratios (HR) with 95% confidence intervals (CI). Potential confounders such as age, sex, education, diabetes, cardiovascular disease and stroke were included in adjusted models. In genotyped subsamples (n = 2977 in STR-1973; n = 10,366 in SALT), APOE ε4 status was considered in models. A total of 983 (7.4%) and 1979 (4.8%) dementia cases were identified after a median of 41.2 and 14.1 years follow-up in the STR-1973 and SALT sample, respectively. Ever shift work (HR 1.36, 95% CI 1.15-1.60) and night work (HR 1.12, 95% CI 1.01-1.23) were associated with higher dementia incidence. Modest dose-response associations were observed, where longer duration shift work and night work predicted increased dementia risk. Among APOE ε4 carriers, individuals exposed to ≥ 20 years of shift work and night work had increased dementia risk compared to day workers. Findings indicate that shift work, including night shift work, compared to non-shift jobs is associated with increased dementia incidence. Confirmation of findings is needed.

Shift work and cognitive aging: a longitudinal study.

Objectives The few studies of shift work and late life cognitive functioning have yielded mixed findings. The aim of the present study is to estimate the association between shift-work experience and change in cognitive performance before and after retirement age among older adults who were gainfully employed. Methods Five hundred and ninety five participants with no dementia were followed up for a mean of 17.6 standard deviation (SD) 8.8 years from a Swedish population-based sample. Participants had self-reported information on any type of shift-work experience (ever/never) in 1984 and measures of cognitive performance (verbal, spatial, memory, processing speed, and general cognitive ability) from up to 9 waves of cognitive assessments during 1986-2012. Night work history (ever/never) from 1998-2002 was available from a subsample (N=320). Early adult cognitive test scores were available for 77 men. Results In latent growth curve modeling, there were no main effects of "any-type" or night shift work on the mean scores or rate of change in any of the cognitive domains. An interaction effect between any-type shift work and education on cognitive performance at retirement was noted. Lower-educated shift workers performed better on cognitive tests than lower-educated day workers at retirement. Sensitivity analyses, however, indicated that the interactions appeared to be driven by selection effects. Lower-educated day workers demonstrated poorer cognitive ability in early adulthood than lower-educated shift workers, who may have selected jobs entailing higher cognitive demand. Conclusion There was no difference in late-life cognitive aging between individuals with a history of working shifts compared to those who had typical day work schedules during midlife.

Association Between Sleep Characteristics and Incident Dementia Accounting for Baseline Cognitive Status: A Prospective Population-Based Study.

BACKGROUND: Although research has shown that sleep disorders are prevalent among people with dementia, the temporal relationship is unclear. We investigated whether atypical sleep characteristics were associated with incident dementia while accounting for baseline cognitive functioning. METHODS: Screening Across the Lifespan Twin (SALT) study participants were 11,247 individuals from the Swedish Twin Registry who were at least 65 years at baseline (1998-2002). Sleep and baseline cognitive functioning were assessed via the SALT telephone screening interview. Data on dementia diagnoses came from national health registers. Cox regression was performed to estimate hazard ratios for dementia. RESULTS: After 17 years of follow-up, 1,850 dementia cases were identified. Short (≤6 hours) and extended (>9 hours) time in bed (TIB) compared to the middle reference group (hazard ratio = 1.40, 95% confidence interval = 1.06-1.85; hazard ratio = 1.11, 95% confidence interval = 1.00-1.24, respectively) and rising at 8:00 AM or later compared to earlier rising (hazard ratio = 1.12, 95% confidence interval = 1.01-1.24) were associated with higher dementia incidence. Bedtime, sleep quality, restorative sleep, and heavy snoring were not significant predictors. Findings stratified by baseline cognitive status indicated that the association between short TIB and dementia remained in those cognitively intact at the start. CONCLUSIONS: Short and extended TIB and delayed rising among older adults predicted increased dementia incidence in the following 17 years. The pattern of findings suggests that extended TIB and late rising represent prodromal features whereas short TIB appeared to be a risk factor for dementia.

The type A behavior pattern and cardiovascular disease as predictors of dementia.

OBJECTIVE: Research has suggested that greater psychophysiological reactivity to stress increases risk of dementia and that those with the Type A behavior pattern (TABP) are predisposed to elevated stress reactivity and cardiovascular disease (CVD), but no study has evaluated the associations among TABP, CVD, and dementia, prospectively. Hence, the present study aimed to investigate dementia risk in relation to TABP and CVD. METHODS: A population-based cohort of 1,069 persons with a baseline mean age of 64.81 years from the Swedish Twin Registry was followed consecutively for up to 23 years. Based on self-reported items, TABP was measured using 6 scales: Ambition, Stress, Hard-driving, Neuroticism, Cynicism, and Paranoia. CVD was self-reported and dementia was diagnosed adhering to Diagnostic and Statistical Manual of Mental Disorders, third edition, revised (DSM-III-R) or Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV) criteria. RESULTS: TABP was generally not associated with dementia risk. However, significant interaction effects of stress, paranoia, and cynicism with CVD on dementia risk were observed. That is, for those with CVD, high scores on stress, paranoia, and cynicism were associated with increased risk of dementia (hazard ratio [HR] = 1.43, 95% confidence interval [CI] = 0.95-2.15; HR = 1.39, 95% CI = 0.83-2.33; HR = 1.25, 95% CI = 0.76-2.06, respectively), whereas for those who did not have CVD, high scores on these measures appeared to be protective (HR = 0.76, 95% CI = 0.50-1.14; HR = 0.55, 95% CI = 0.34-0.89; HR = 0.50, 95% CI = 0.29-0.84, respectively). CONCLUSION: Some features of TABP confer an increased risk for dementia in those with CVD, whereas those without CVD are protected. When evaluating the risk of dementia, CVD and personality traits should be taken into consideration.