Serhiy Dekhtyar

Association of lifelong exposure to cognitive reserve-enhancing factors with dementia risk: A community-based cohort study

Background Variation in the clinical manifestation of dementia has been associated with differences in cognitive reserve, although less is known about the cumulative effects of exposure to cognitive reserve factors over the life course. We examined the association of cognitive reserve-related factors over the lifespan with the risk of dementia in a community-based cohort of older adults. Methods and findings Information on early-life education, socioeconomic status, work complexity at age 20, midlife occupation attainment, and late-life leisure activities was collected in a cohort of dementia-free community dwellers aged 75+ y residing in the Kungsholmen district of Stockholm, Sweden, in 1987–1989. The cohort was followed up to 9 y (until 1996) to detect incident dementia cases. To exclude preclinical phases of disease, participants who developed dementia at the first follow-up examination 3 y after the baseline were excluded (n = 602 after exclusions). Structural equation modelling was used to generate latent factors of cognitive reserve from three periods over the life course: early (before 20 y), adulthood (around 30–55 y), and late life (75 y and older). The correlation between early- and adult-life latent factors was strong (γ = 0.9), whereas early–late (γ = 0.27) and adult–late (γ = 0.16) latent factor correlations were weak. One hundred forty-eight participants developed dementia during follow-up, and 454 remained dementia-free. The relative risk (RR) of dementia was estimated using Cox models with life-course cognitive reserve-enhancing factors modelled separately and simultaneously to assess direct and indirect effects. The analysis was repeated among carriers and noncarriers of the apolipoprotein E (APOE) ε4 allele. A reduced risk of dementia was associated with early- (RR 0.57; 95% CI 0.36–0.90), adult- (RR 0.60; 95% CI 0.42–0.87), and late-life (RR 0.52; 95% CI 0.37–0.73) reserve-enhancing latent factors in separate multivariable Cox models. In a mutually adjusted model, which may have been imprecisely estimated because of strong correlation between early- and adult-life factors, the late-life factor preserved its association (RR 0.65; 95% CI 0.45–0.94), whereas the effect of midlife (RR 0.73; 95% CI 0.50–1.06) and early-life factors (RR 0.76; 95% CI 0.47–1.23) on the risk of dementia was attenuated. The risk declined progressively with cumulative exposure to reserve-enhancing latent factors, and having high scores on cognitive reserve-enhancing composite factors in all three periods over the life course was associated with the lowest risk of dementia (RR 0.40; 95% CI 0.20–0.81). Similar associations were detected among APOE ε4 allele carriers and noncarriers. Limitations include measurement error and nonresponse, with both biases likely favouring the null. Strong correlation between early- and adult-life latent factors may have led to a loss in precision when estimating mutually adjusted effects of all periods. Conclusions In this study, cumulative exposure to reserve-enhancing factors over the lifespan was associated with reduced risk of dementia in late life, even among individuals with genetic predisposition.

Cognitive Reserve: A Life-Course Perspective

The concept of reserve has been developed to account for the discontinuity between the extent of brain damage at its clinical manifestation in the form of cognitive decline or dementia . In this chapter, we discuss contributors to cognitive reserve from various stages of the life-course , including childhood, early adulthood, middle age, and late life. Evidence from observational, as well as intervention trials is presented and assessed. We conclude by arguing that reserve formation in dementia risk is a life-course process whereby baseline cognitive abilities are subjected to modulation by subsequent experiences at diverse stages over the entire life-course. Variations among individuals in their ability to withstand age-related brain changes is ultimately dependent on their life-time accumulation of mental, physical, and lifestyle inputs into cognitive reserve.

Letter to the EditorResponse to Brodziak's Letter to the Editor

How to Prove that Good Learning Outcomes in Childhood Is an Independent Factor Strengthening the Cognitive Reserve Response

Response to "How to Prove that Good Learning Outcomes in Childhood Is an Independent Factor Strengthening the Cognitive Reserve".

How to Prove that Good Learning Outcomes in Childhood Is an Independent Factor Strengthening the Cognitive Reserve Response

How to Prove that Good Learning Outcomes in Childhood Is an Independent Factor Strengthening the Cognitive Reserve Response

How to Prove that Good Learning Outcomes in Childhood Is an Independent Factor Strengthening the Cognitive Reserve Response

Response to Brodziak's Letter to the Editor

How to Prove that Good Learning Outcomes in Childhood Is an Independent Factor Strengthening the Cognitive Reserve Response

A life-course study of cognitive reserve in dementia: Dementia incidence in inpatient registers and mmse test scores in a clinical study in sweden

Cognitive reserve helps mitigate the impact of pathology on the clinical expression of dementia. Education and occupational complexity are considered as contributors to reserve, although it has been argued that cognitive reserve is likely formed over the life-course. A life-course model of cognitive reserve in dementia risk has not yet been tested. We apply a life-course model and examine if school grades around age 10, formal educational attainment, and lifetime occupational complexity affect dementia incidence in inpatient registers.