First-hand information on cognitive screening and several relevant references were provided by the World Federation of Neurology Dementia Research Group members and co-authors. A systematic literature search of PubMed and Medline was also done with combinations of search terms, including “developing countries” and “dementia”, with topic headings including “Alzheimer's disease”, “prevalence”, “incidence”, “cognitive impairment”, “mortality”, “risk factors”, “vascular dementia”, “Asia”,
ReviewAlzheimer's disease and vascular dementia in developing countries: prevalence, management, and risk factors
Introduction
Older people with dementia exist in nearly every country in the world. Dementia rates are predicted to increase at an alarming rate in the least developed and developing regions of the world despite mortality resulting from malnutrition, poverty, war, and infectious diseases. WHO projections suggest that by 2025, about three-quarters of the estimated 1·2 billion people aged 60 years and older will reside in developing countries.1 Thus, by 2040, if growth in the older population continues, and there are no changes in mortality or burden reduction by preventive measures, 71% of 81·1 million dementia cases will be in the developing world.2 About 4·6 million new cases of dementia are added every year, with the highest growth projections in China and its south Asian neighbours. These projections might be confounded by temporal changes due to shorter survival after dementia,3 lack of education and awareness, inadequate diagnostic assessment,4 and variability in costs of care of the elderly with dementia,5 all of which could lead to under-accounting of the dementia burden.6 In China, for example, 49% of patients with dementia were classified as normally ageing and only 21% had adequate access to diagnostic assessment,7 compared with 20% and more than 70%, respectively, in Europe.8
There are no known curative or preventive measures for most types of dementia. Diet and lifestyle could influence risk, and studies suggest that midlife history of disorders that affect the vascular system, such as hypertension, type 2 diabetes, and obesity, increase the risk for dementia including Alzheimer's disease (AD).9, 10, 11, 12 Increased trends in demographic transition and urbanisation within many developing countries are predicted to lead to lifestyle changes.13 Delaying of onset, by modifying risk or lifestyle, decreases the prevalence and public health burden of dementia; a delay in onset of 1 year would translate to almost a million fewer prevalent cases in the USA.14 However, this in turn might increase demands on health services and costs for older populations.15
We review published prevalence estimates and modifying factors for brain ageing-related dementias in developing regions of the world, as defined by the United Nations.16 Our report is limited to ageing-related neurodegenerative and vascular dementias and does not address dementia secondary to retroviruses (eg, HIV) or other infectious agents, recognising that these might assume importance in younger adults or in specific regions. Other reviews have focussed on these issues,15, 17, 18 but we take particular note of genetic and environmental factors,18, 19 in addition to the problems encountered in accounting for differences in dementia occurrence between developed and developing countries. Although more data from developing countries are needed, several comparative dementia prevalence and risk-factor assessment projects, which use similar designs, survey methods, and investigators, have been invaluable resources to allow examination of phenotypic variations in dementias in populations living in very different cultures and environments.18, 20, 21, 22
Section snippets
Dementia screening
Neuropsychometric assessment seems to be the best method to screen individuals in most developing countries.23 At the outset, the lack of standardisation of screening tools has to be recognised as a major issue in the estimation of the true burden.20 Standardisation might not be readily achieved because of diversity of language, culture, and levels of literacy. In certain communities, more than 80% of elderly people do not read or write.24 The mini mental state examination (MMSE) has been
Dementia prevalence and incidence
Since the Delphi study projections,2 several large-scale dementia prevalence studies have been done.30, 31, 32, 33, 34, 35, 36, 37, 38, 39 Dementia prevalence estimates vary widely within developing countries (table 1). This variation might indicate differences in population age structure, genetics, and lifestyle, but could also be due to difficulty in standardising dementia assessment and reduced survival after diagnosis.15 The mean age-adjusted prevalence estimate for dementia among people
Alzheimer's disease
Late-onset AD is the most common subtype of age-related dementia, even in developing countries; 60% of all cases of dementia fulfilled the US National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS–ADRDA) criteria.78 Total population projections suggest that 3·1 million people in China could have AD. Although unusually high prevalence was apparent in some countries, the mean AD prevalence was estimated to be
Behavioural and psychological symptoms of dementia
Behavioural and psychological symptoms of dementia (BPSDs) are common among people with dementia in developing countries, although there seem to be marked regional variants.22, 107 Several factors, including methods of reporting and cultural taboos, might account for the variations. However, at least one BPSD was reported in 70% of participants from 17 developing countries, and at least one case-level AGECAT psychiatric syndrome was shown by nearly half of those with dementia.27 Depression
Early stages of dementia and mild cognitive impairment
The transition or prodromal stage between normal ageing and dementia or mild cognitive impairment (MCI) is a heterogeneous entity. Diagnostic criteria and standardisation of MCI are evolving, which makes direct comparisons among studies more difficult, possibly due to the stronger influence of illiteracy and socioeconomic factors, than in similar studies when dementia is diagnosed. Patients and families in developing countries are also less likely to admit or report cognitive difficulties
Age and sex
Exposure early in life to deleterious conditions related to poverty, including infectious diseases, malnutrition, and prenatal stress, might influence the ageing process and reduce longevity for people in developing countries.116, 117 Despite these realities, increasing age is the most consistent risk factor for dementia worldwide (table 2). Age was also a strong risk factor,30, 51 with dementia prevalence of 2–11%, in those aged under 65 years. Nearly all studies in Latin America, Africa, and
Use of herbs and medicinal plants for dementia
Developing countries tend to retain traditional herbal medical practices and thus offer an invaluable resource for new anti-dementia therapies.185 However, the usefulness of such a resource relies on documented evidence of the effects. One of the largest long-term controlled clinical trials in progress on dementia prevention is based on the Asian traditional tree medicine Gingko biloba.186 Preliminary data have indicated significant effects on dementia progression,187 but the most recent
Mortality and dementia
Dementia modifies survival and increases the risk of death. A study among Shanghai residents indicated that the mortality risk ratios for AD and VaD, particularly in those over 75 years of age, were similar to the mortality risk ratio for cancer.125 In another Chinese study, the risk for death in patients with dementia was reported to be three times higher than in the whole cohort, although not related to a specific cause.84 In Brazilians, dementia was determined to be the most significant
Costs of dementia
Current projections indicate that the burden of disease, expressed as WHO-designated disability-adjusted life-years (DALYs), is unequally distributed between middle-income and low-income countries (table 3).16, 200 However, if dementia prevalence in developing countries is assumed to increase substantially due to demographic transition, the DALYs per number of patients with dementia who are 65 years and older are similar between regions.5 To estimate the total costs, we modelled the societal
Dementia awareness, care, and services
Understanding the burden and costs of dementia is crucial to guide future health care and socioeconomic policy.27 Policymakers need evidence to prioritise and plan appropriately for the rapidly growing numbers of older people with dementia and other chronic diseases. Low public awareness, under-diagnosis, and under-treatment could be addressed by national mobilisation strategies to increase awareness and specialised training for heath professionals and authorities through mass media, scientific
Conclusions
The prevalence of dementia, particularly that of AD, is increasing in the developing countries of Asia and Latin America. However, reliable age-adjusted estimates indicate a low prevalence of dementia in India and sub-Saharan Africa. Difficulties in definition, ascertainment of decline in intellectual ability, and assessment of patients mean that meagre information on MCI is available in developing countries.20 Illiteracy and depressive illness remain strong risks for dementia. Further research
Search strategy and selection criteria
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