Effect of retirement on cognitive function: the Whitehall II cohort study
European Journal of Epidemiology
Effect of retirement on cognitive function: the Whitehall II cohort study
Baowen Xue 0 1 2 3
Dorina Cadar 0 1 2 3
Maria Fleischmann 0 1 2 3
Stephen Stansfeld 0 1 2 3
Ewan Carr 0 1 2 3
Mika Kivim a¨ki 0 1 2 3
Anne McMunn 0 1 2 3
Jenny Head 0 1 2 3
Retirement 0 1 2 3
0 Department of Behavioural Science and Health, Institute of Epidemiology and Health Care, School of Life and Medical Sciences, University College London , London , UK
1 Biostatistics and Health Informatics, Institute of Psychiatry, Psychology and Neuroscience, King's College London , London , UK
2 Research Department of Epidemiology and Public Health, Institute of Epidemiology and Health Care, School of Life and Medical Sciences, University College London , London , UK
3 Centre for Psychiatry, Wolfson Institute of Preventive Medicine, Barts and the London School of Medicine and Dentistry, Queen Mary University of London , London , UK
reasoning, phonemic verbal fluency, and semantic verbal fluency before and after retirement. We found that all domains of cognition declined over time. Declines in verbal memory were 38% faster after retirement compared to before, after taking account of age-related decline. In analyses stratified by employment grade, higher employment grade was protective against verbal memory decline while people were still working, but this 'protective effect' was lost when individuals retired, resulting in a similar rate of decline post-retirement across employment grades. We did not find a significant impact of retirement on the other cognitive domains. In conclusion, these findings are consistent with the hypothesis that retirement accelerates the decline in verbal memory function. This study points to the benefits of cognitively stimulating activities associated with employment that could benefit older people's memory.
Cognition; Longitudinal study; Piecewise regression; Employment grade
Introduction
Good cognitive functioning represents an essential element
of healthy ageing and independent living [
1
]. There is some
evidence that ageing affects cognitive functions that are
primarily associated with executive processing and other
functions of the frontal lobe [
2, 3
]. Thus, fluid abilities,
such as memory, processing speed, and spatial ability tend
to decline faster with age than crystallised functions,
including vocabulary, information and comprehension
[
4–6
]. However, the decline in these abilities is not
necessarily homogenous across the population, as some people
maintain cognitive vitality even into extreme old age [
7–9
].
On the one hand, there is evidence that the adult brain
shows neuroplasticity and neurogenesis, representing the
brain’s ability to generate new neurons and rewire itself
[
10–12
]. On the other hand, accelerated deterioration or
impairment in one or more cognitive functions beyond the
‘normal’ age-related decline could be predictive of the
onset of dementia, a major cause of disability and
dependency among older people worldwide [
13, 14
].
Therefore, it is important to identify and understand the
predictors of interindividual differences in cognitive
decline.
The theory of cognitive reserve proposes that some
individuals have a larger cognitive reserve than others. It
has been postulated that innate cognitive resources (such as
childhood IQ), cognitive stimulation during brain
maturation in childhood (such as education), and cognitively
engaged lifestyle during adulthood (such as cognitively
demanding occupation) can increase cognitive reserve, thus
building up a buffer against cognitive decline in old age
[
15, 16
]. The ‘use it or lose it’ hypothesis similarly
suggests that a person can maintain cognitive function by
engaging in cognitively demanding activities, whereas
failing to keep mentally active will detrimentally affect
cognitive function and could accelerate cognitive decline
or even the onset of dementia [17]. Accordingly, retirement
may be a potential trigger for cognitive decline, assuming
that retirees leave paid work that is cognitively demanding.
Many studies have supported this assumption showing that
retirement is associated with lower cognitive functioning
[
18–23
], and later retirement is associated with better
cognition and lower risk of dementia [
24–27
], although
some studies have found no association [
28, 29
] or even a
positive effect [30] of retirement on levels of cognition.
When studying the effects of retirement on cognition, it
is important to consider reverse causality. Declines in
cognitive function may negatively affect the management
of work tasks and thus could be a determinant of the
decision to retire [
31, 32
]. For example, chronic diseases,
such as stroke, might affect both cognitive function and
retirement decisions [
33, 34
]. The vast majority of studies
have compared retirees with working people to assess the
potential effect of retirement on cognition, and it is
possible that their r (...truncated)