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Background Current 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. Methods We carried out a systematic review of studies of trends in prevalence, incidence and mortality for people with dementia, conducted since 1980. Results We 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. Conclusions We 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.

Background In low or middle income countries chronic diseases are rapidly becoming the main cause of disease burden. However, the main focus of health policymakers has been on preventing death from cancer and heart disease, with very little attention to the growing problem of long-term needs for care (dependence). Numbers of dependent older people are set to quadruple by 2050. The economic impact of providing long-term care is likely to be substantial. Methods/design The study uses mixed methods and draws on and extends the population-based surveys conducted by the 10/66 Dementia Research Group. We focus on two countries in Latin America (Peru and Mexico), China and Nigeria. The surveys comprised baseline surveys of health, socioeconomic circumstances and care arrangements, repeated three to four years later. We are going back to these households to make a detailed assessment of the overall economic status and the use of health services by all family members. We will compare households where: a) an older resident became dependent between baseline and follow-up (incident care), b) one or more older people were dependent at both time points (chronic care), b) c) no older residents had needs for care (control households) for household income, consumption, healthcare expenditure and economic strain. In each of the four countries we are carrying out six detailed household ‘case studies’ to explore in more depth the economic impacts of dependence, and the social relations between household members and others in their network. Discussion The INDEP study will provide a detailed examination of the economic and social effects of care dependence in low and middle income settings. As the proportion of older people with needs for care rises rapidly in these countries, this neglected policy area is likely to become increasingly salient for families, communities and policymakers alike. Our detailed multilevel plans for dissemination will ensure that the study helps to put this important issue on the agenda for the international and national media, the public and researchers. Electronic supplementary material The online version of this article (doi:10.1186/2193-1801-3-379) contains supplementary material, which is available to authorized users.