The changing prevalence and incidence of dementia over time — current evidence

Key Points Knowledge of changes in dementia occurrence can only be acquired through population-based studies conducted at different time periods in representative samples derived from the same populations Such studies must use diagnostic and research methods that are as similar as feasible across time to enable valid comparisons We synthesize worldwide evidence from 14 such population-based studies across Western Europe, the USA, Japan and Nigeria; most have reported declining or stable prevalence and incidence with varying sex differences across countries No single risk or protective factor has explained these changes, but societal changes in western societies have improved cognitive reserve and health status across the lifecourse Integrating analytical epidemiological approaches and neuroscience within population-based studies is key to understanding the changes observed, underlying neurobiological mechanisms, and what policies might sustain such improvements Determining how the incidence and prevalence of dementia changes over time requires population-based studies that use consistent methods over time. In this Review, the authors discuss the results of 14 worldwide studies that have attempted this approach. The findings consistently indicate that the incidence and prevalence of dementia, at least in Western countries, is stable or declining. Dementia is an increasing focus for policymakers, civil organizations and multidisciplinary researchers. The most recent descriptive epidemiological research into dementia is enabling investigation into how the prevalence and incidence are changing over time. To establish clear trends, such comparisons need to be founded on population-based studies that use similar diagnostic and research methods consistently over time. This narrative Review synthesizes the findings from 14 studies that investigated trends in dementia prevalence (nine studies) and incidence (five studies) from Sweden, Spain, the UK, the Netherlands, France, the USA, Japan and Nigeria. Besides the Japanese study, these studies indicate stable or declining prevalence and incidence of dementia, and some provide evidence of sex-specific changes. No single risk or protective factor has been identified that fully explains the observed trends, but major societal changes and improvements in living conditions, education and healthcare might have favourably influenced physical, mental and cognitive health throughout an individual's life course, and could be