BOSTON—Midlife shift work is associated with an increased risk of incident dementia in later life, according to research presented at the 31st Annual Meeting of the Associated Professional Sleep Societies. The
association is stronger with longer duration of shift
work, said Kathleen Bokenberger, a doctoral student in
the Department of Medical Epidemiology and Biostatis-tics at the Karolinska Institutet in Stockholm.
“To the best of our knowledge, this is the first study
to find a connection between shift work and greater
dementia incidence,” said Ms. Bokenberger. “As such,
we will need confirmation from other studies, especially
if they have more nuanced measures of shift work, and
perhaps repeated measures of shift work.”
An Analysis of Two Population-Based Cohorts
Shift work interferes with the circadian and homeostatic
regulation of sleep and can lead to insomnia and excessive sleepiness. A prospective Danish study found that
rotating and evening shift work were associated with
increased dementia mortality, but the link between shift
work and dementia is still relatively unexplored, said
She and her colleagues followed two population-based cohorts from the Swedish Twin Registry. The
first cohort, which the researchers called STR-1973,
included 13,283 people who were age 30 or older
when they received a mailed questionnaire in 1973
that elicited information about shift work status and
duration. The Screening Across the Lifespan Twin
(SALT) sample included 41,199 participants who participated in a telephone interview between 1998 and
2002 that asked about status and duration of night
The primary outcome was all-cause dementia, and
dementia diagnoses were obtained from Swedish national health registers. Investigators followed participants until the date of dementia diagnosis, death, or
the end of follow-up in 2015.
A Dose-Response Relationship
The mean age at baseline was 38 in the STR-1973 cohort
and 58 in the SALT cohort. Median follow-up time was
41 years in the STR-73 cohort and 14 years in the SALT
cohort. The proportion of participants with shift work
history was 17% in the STR-1973 cohort. The proportion of people who worked nights was 30% in the SALT
cohort. Dementia incidence was 7.4% in the STR-1973
cohort and 5.0% in the SALT cohort.
The researchers used Cox proportional hazard models to analyze the data and adjust for age, sex, education,
cardiovascular disease, stroke, and type 2 diabetes. Having shift work versus day work was associated with an
increased hazard of dementia (hazard ratio [HR], 1.40),
as was having night work versus day work (HR, 1. 13).
Spline models indicated modest dose-response relationships in which longer duration of shift work and night
work predicted greater dementia risk.
Information about APOE e4 genotype was available for
subsamples of both cohorts. APOE e4 seemed to be an effect
modifier for the association of night work and dementia, but
not for that of shift work and dementia. APOE e4 carriers
with 20 or more years of shift work had a fourfold increased
risk of dementia. APOE e4 carriers with 20 or more years of
night work had a twofold increased risk of dementia. The
sample sizes were small, however, and “it is possible that
these findings are spurious,” said Ms. Bokenberger.
“Individuals in the labor force might consider minimizing shift work exposure or managing work scheduling practices, but this is dependent on individual differences and tolerances to certain types of shift work,”
she concluded. NR
Bokenberger K, Ström P, Dahl Aslan AK, et al. Shift work and cognitive aging: a
longitudinal study. Scand J Work Environ Health. 2017 Mar 31 [Epub ahead of print].
Jørgensen JT, Karlsen S, Stayner L, et al. Shift work and overall and cause-specific mortality in the Danish nurse cohort. Scand J Work Environ Health.
Shift Work in Midlife
Increases Risk of Dementia
The risk of dementia appears to increase with longer duration of shift work.