Conclusion These results show that self reported engagement is not associated with the trajectory of cognitive decline in late life, but is associated with the acquisition of ability during the life course. Overall, findings suggest that high performing adults engage and those that engage more being protected from relative decline.

Results Intellectual engagement was significantly associated with level of cognitive performance in later life, with each point on a 24 point scale accounting for 0.97 standardised cognitive performance (IQ-like) score, for processing speed and 0.71 points for memory (both P<0.05). Engagement in problem solving activities had the largest association with life course cognitive gains, with each point accounting for 0.43 standardised cognitive performance score, for processing speed and 0.36 points for memory (both P<0.05). However, engagement did not influence the trajectory of age related decline in cognitive performance. Engagement in intellectual stimulating activities was associated with early life ability, with correlations between engagement and childhood ability and education being 0.35 and 0.22, respectively (both P<0.01).

Introduction

Loss of mental competence can cause substantial anticipatory concern among older adults (that is, age> 65 years) by suggesting that such loss heralds the onset of progressive cognitive decline and dementia.1 Public health guidance on successful ageing highlights the importance of social and physical activity and engagement.2 Cognitive endeavours that engage multiple activity domains might have important benefits.3 However, longitudinal analysis of potential protective effects of cognitively effortful pursuits is difficult and a variety of methodological challenges have been documented. In studies4 that track cognitive change in adulthood, there are a dearth of historical data on childhood mental ability and limited awareness that early performances on IQ-type tests are already confounded by reading proficiency acquired before IQ-type scores can be obtained.

Another concern is the potential practice effects that can result from exposure to a common test format, and the possibility that differences in initial cognitive ability influence the size of practice effects observed.5 Results presented by Wesnes and Pincock in 20026 suggest that improvements in practice effects for commonly used tests of processing speed and memory are largest between the first and second occasion, with little improvement after that. Modelling of longitudinal data allows such practice effects to be accounted for by an initial practice model.7 Finally, reports of the effects of additional common confounders such as education and sex on cognitive performance are mixed, but it is generally accepted that education and sex affect cognitive performance in particular domains8 and early education has an influence across the life course.9

Activity engagement is so often argued to be an important dimension of successful ageing10 (and more specifically, the preservation of intellectual function in old age11121314151617) that the “use it or lose it” conjecture already appears to be an established fact of cognitive ageing. We aimed to re-examine this claim by analysing the effects of activity engagement on cognitive test performance and the trajectory of that performance in late adulthood. In addition, we aimed to test the robustness of observations by controlling for life course cognition and education.

Various studies support the “use it or lose it” conjecture. For example, Stanovich and colleagues proposed in 1995 that literary habits and exposure to print might be one way in which cognitive capacities are maintained with age.18 In their cross sectional study including a sample of younger and older adults, the researchers found that measures of exposure to print was associated with the positive relations between age and vocabulary, and between age and declarative knowledge. In 1997, Christensen and colleagues assessed the influence of self reported and informant reported activity levels on crystallised intelligence, fluid intelligence, memory, and mini-mental state examination scores in a sample of community dwelling, older participants. They found that specific activities were associated with higher cognitive performance in less well educated participants, but had no effect on cognitive performance in highly educated participants.12 In 2003, Verghese and colleagues conducted a prospective cohort study of older adults who resided in the community and did not have dementia at baseline.17 They reported that even after statistically controlling for educational level, presence or absence of chronic medical illnesses, and baseline cognitive status, those individuals who participated at least twice weekly in cognitive activities such as reading, playing board games, and playing musical instruments had significantly reduced risks for dementia.13

Our collaborators, who studied survivors sampled from the Scottish Mental Surveys, have also examined possible links between activity engagement and cognitive functioning in later life. Their study identified typical intellectual engagement scores (recorded on a self report questionnaire) and childhood mental ability as powerful effects on verbal fluency scores in late life.19 The evidence is clear that there is an association between typical intellectual engagement and cognitive ability in late life, although data on the longitudinal trajectory of cognitive change are sparse. However, the strength of any association between engagement and cognition is unclear, and it may well be that both cognition and engagement share a common origin (eg, early ability or education).

With access to archives of childhood mental ability and repeated measurement of cognitive ability in late adulthood, we aimed to investigate the possible effects of childhood ability, education, sex, and practice as a result of repeated cognitive testing when investigating the influence of typical intellectual engagement on late life cognition and the trajectory of decline. We analysed trajectories for two cognitive tests used repeatedly on our study group: the auditory verbal learning test as an indicator of memory performance, and the digit symbol substitution test as a measure of mental speed. Both tests are known to be sensitive to the effects of ageing and are measures of fluid ability.20