Markers of cognitive reserve and dementia incidence in the English Longitudinal Study of Ageing

Background In the current climate of an ageing population, it is imperative to identify preventive measures for dementia. Aims We implemented a multifaceted index of cognitive reserve markers and investigated dementia incidence over 15 years of follow-up in a representative sample of the English population. Method Data were 12 280 participants aged >= 50 years from the English Longitudinal Study of Ageing, free from dementia at their baseline assessments during wave 1 (2002-2003), 3 (2006-2007) or 4 (2008-2009), and followed up until wave 8 (2016-2017). The Cognitive Reserve Index was constructed as a composite measure of education, occupation and leisure activities, using a standardised questionnaire. Cox proportional hazards regression models were used to estimate the hazard ratios of dementia in relation to cognitive reserve levels (low, medium and high) and its components (education, occupation and leisure activities). Results During the follow-up period, 602 participants aged 56-99 years developed dementia. Higher levels of cognitive reserve (hazard ratio 0.65, 95% CI 0.48-0.89, P = 0.008) were associated with a lower risk of dementia. An individual analysis of its components showed that higher levels of education (hazard ratio 0.56, 95% CI 0.36-0.88, P = 0.012), occupation (hazard ratio 0.72, 95% CI 0.56-0.91, P = 0.008) and leisure activities (hazard ratio 0.74, 95% CI 0.56-0.99, P = 0.047) were predictive of a reduced dementia risk, with the first two components particularly protective in younger participants (<85 years). Conclusions This study showed a reduced risk of dementia for individuals with a higher level of cognitive reserve, represented by higher education, complex occupations and multifaceted level of leisure activities.