CHAPTER 2 EPIDEMIOLOGY OF DEMENTIA
<strong>Dementia</strong>: A public health priority > CHAPTER 2 > EPIDEMIOLOGY OF DEMENTIA <strong>Dementia</strong> mainly affects older people, although there is growing awareness of cases that start before the age of 65. Population ageing is having a profound impact on the emergence of the global dementia epidemic, influencing awareness and driving demand for services. Particularly rapid increases in the numbers and proportions of older people are forecast for China, India and Latin America (11). By 2050 people aged 60 and over will account for 22% of the world’s population, four-fifths living in Africa, Asia or Latin America. As yet, public and policy-maker awareness of dementia and health system preparedness for it are much more limited in these regions where the epidemic will be concentrated in the coming decades. It is therefore important to track the global prevalence and impact of this burdensome condition and its regional distribution in the context of rapidly unfolding demographic and health transitions. Global prevalence of dementia Late onset dementia In 2005, Alzheimer’s Disease International (ADI) commissioned a panel of experts to review all available epidemiological data and reach a consensus estimate of prevalence in each of 14 world regions (12). The panel estimated 24.3 million people aged 60 years and over with dementia in 2001, 60% living in LMIC. Each year, 4.6 million new cases were predicted, with numbers affected nearly doubling every 20 years to reach 81.1 million by 2040. Incidence was estimated from prevalence and mortality. The estimates were provisional, due to limited data (12). Coverage was good in Europe, North America, and in developed Asia-Pacific countries. Studies from China and India were too few and estimates too variable to provide a consistent overview. There was a dearth of studies from Latin America (13–15), Africa (16), Eastern Europe, Russia and the Middle East, and a consequent reliance on the consensus judgement of the international expert panel. This supported a tendency, noted in the few LMIC studies available at that time, for the age-specific prevalence of dementia to be lower in developing countries than in developed ones (16–18). Global prevalence is being reappraised for the revision of the Global burden of disease (GBD) study 2010 (http: //www.globalburden.org/), with findings summarized in ADI’s 2009 World Alzheimer Report (3). The evidence base was expanded considerably with more studies from LMIC and from other regions and groups previously underrepresented in the literature. Enhancements included a fully systematic review of the world literature on the prevalence of dementia (1980– 2009) in 21 GBD regions, a critical appraisal of study quality, and an attempt, where possible, to generate regional estimates from quantitative meta-analysis. Details of the methodology can be found in the web appendix¹. Search results The search yielded abstracts for 2017 publications. Of these, 155 publications (describing 167 studies) were considered to be provisionally eligible. For 20 of these publications, it was not possible to confirm eligibility. A full list of included and excluded publications is provided in the web appendix¹. Finally, 135 publications (describing 147 studies) were fully eligible for inclusion in the review. Coverage Good-to-reasonable coverage was identified for 11 of the 21 GBD regions (Tables 2.1 and 2.2). Western Europe (56 studies) and East Asia (34 studies) accounted for most of the world’s studies. The next best represented region was Asia Pacific High Income (22 studies), followed by North America (13 studies), and Latin America (11 studies – comprising three in the Andean, four in the Central, one in the Southern and three in the Tropical Latin America region). Other regions with reasonable coverage were South Asia (7 studies), South-East Asia (5 studies) and Australasia (4 studies). Five regions were sparsely covered; the Caribbean (4 studies as three of the four studies were conducted in Cuba, and the other in the Dominican Republic, thus only two countries were covered from the region), Central Europe (4 studies), North Africa / Middle East (2 studies), Eastern Europe (1 study) and Western sub-Saharan Africa (2 studies) and Southern sub-Saharan Africa (1 study). No eligible studies were identified for Central and Eastern sub-Saharan Africa, or for Central Asia. Figure 2.1, summarizing the annual number of prevalence studies according to the median year in which data were collected, indicates a large and sustained increase in studies conducted in LMIC since the mid-1990s, while studies in high-income countries peaked in the early 1990s and declined sharply thereafter; 27% of studies in high-income countries (chiefly in Europe and North America) were conducted in the 1980s, 63% in the 1990s and 10% in the 2000s. 1. http://www.who.int/mental_health/publications/dementia_report_2012 12