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Bill & Melinda Gates Foundation.

We believe that the detailed estimates in this paper constitute the best currently available basis for policymaking, planning, and allocation of health and welfare resources.

The Commission gratefully acknowledges the contribution of data on psychotherapies from Pim Cuijpers, the Global Burden of Disease from Harvey Whiteford, and inputs received from William Eaton on some of the content. We also acknowledge the role of the Lancet editors (Niall Boyce and Helen Frankish) who provided important feedback through the process of developing the Commission. Research administration of the Commission was coordinated by Deepti Beri (Public Health Foundation of India and Sangath).We acknowledge the role of research team members of the working groups who provided assistance with literature searches, drafting and data extraction and helping prepare figures, namely

BackgroundCurrent projections of the scale of the coming dementia epidemic assume that the age- and sex-specific prevalence of dementia will not vary over time, and that population ageing alone (increasing the number of older people at risk) drives the projected increases. The basis for this assumption is doubtful, and secular trends (that is, gradual decreases or increases in prevalence over long-term periods) are perfectly plausible.MethodsWe carried out a systematic review of studies of trends in prevalence, incidence and mortality for people with dementia, conducted since 1980.ResultsWe identified nine studies that had tracked dementia prevalence, eight that had tracked dementia incidence, and four that had tracked mortality among people with dementia. There was some moderately consistent evidence to suggest that the incidence of dementia may be declining in high-income countries. Evidence on trends in the prevalence of dementia were inconsistent across studies and did not suggest any clear overall effect. Declining incidence may be balanced by longer survival with dementia, although mortality trends have been little studied. There is some evidence to suggest increasing prevalence in East Asia, consistent with worsening cardiovascular risk factor profiles, although secular changes in diagnostic criteria may also have contributed.ConclusionsWe found no evidence to suggest that the current assumption of constant age-specific prevalence of dementia over time is ill-founded. However, there remains some uncertainty as to the future scale of the dementia epidemic. Population ageing seems destined to play the greatest role, and prudent policymakers should plan future service provision based upon current prevalence projections. Additional priorities should include investing in brain health promotion and dementia prevention programs, and monitoring the future course of the epidemic to chart the effectiveness of these measures.