While the challenge of dementia in the older English population is widely shared; opposing views are expressed about its trend. We aimed to estimate current dementia prevalence, explored recent trajectory of cognition likeliest to lead to dementia, and examine cohort effects.

The English Longitudinal Study of Ageing (2002–2015) is the primary nationwide longitudinal ageing study, which in the latest wave collected for the first time dementia status in the population. The previous six waves provided instead measures of general cognition to establish decade-long trajectories of cognition (n=12,196).

Dementia is ascertained using the Telephone Interview for Cognitive Status. Dementia in wave seven is predicted by latent trajectories of general cognition over the previous six waves, while controlling for contemporaneous confounders including age, sex, cohort, education, wealth, occupation, marital status, comorbidities, health behaviours, sensory function and social connections (offline and online). Logistic regression with standard errors adjustment for latent trajectories as covariates is used.

The prevalence of dementia in the older English population aged 60–89 is 9.0% (confidence interval, 9.0–9.1%). Risk factors for general cognitive deficits are also responsible for dementia including sedentary behaviour, presence of comorbidities and lack of social connections. In contrast to cohort effects, which show no association, past trajectories of general cognition has the strongest association with dementia in the last wave.

Consistent with the long prodromal stage of dementia, decade-long trajectories of cognition are strongly consequential. Also, online social connections deserve further examination for its potential.