ArticlesGlobal prevalence of dementia: a Delphi consensus study
Introduction
Auguste D, a patient of Alois Alzheimer, was a 51-year-old woman with a 5-year history of progressive cognitive impairment, hallucinations, delusions, and severely impaired social functioning. After her death on April 8, 1906, Alzheimer identified in her brain amyloid plaques, neurofibrillary tangles, and arteriosclerotic changes. World Alzheimer's Day, Sept 21, 2006, marks the centenary of the identification and naming of the clinico-pathological entity that we now recognise to be the main cause of dementia syndrome, and one of the most burdensome conditions of later life.
According to the Global Burden of Disease estimates for the 2003 World Health Report,1 dementia contributed 11·2% of years lived with disability in people aged 60 years and older; more than stroke (9·5%), musculoskeletal disorders (8·9%), cardiovascular disease (5·0%), and all forms of cancer (2·4%). The disability weight for dementia, estimated by an international and multidisciplinary expert consensus, was higher than for almost any other health condition, apart from spinal-cord injury and terminal cancer. Although people with dementia are heavy consumers of health services, direct costs in developed countries arise mostly from community and residential care. Knapp and colleagues2 estimated that in the UK, 224 000 of the 461 000 elderly people with cognitive impairment live in institutions at a cost of £4·6 billion (US$8·2 billion) every year, or 0·6% of the UK gross domestic product. Family caregivers remain the cornerstone of support for people with dementia, experiencing substantial psychological, practical, and economic strain.3, 4 Dementia care is particularly time intensive, and many caregivers need to cut back on work. In the USA, the annual cost of informal care was $18 billion per year in 1998 dollars.5
Such estimates of burden are critically dependent on the accuracy of the estimates of people living with the disease, which in turn depend on evidence from epidemiological surveys that are representative and well organised. For dementia in many world regions, such evidence is either incomplete or scanty in its coverage. Even when a wider evidence base is available for country or region-specific figures, these estimates are sometimes generated from single studies with little regard for their generalisability. Previous estimates of the number of people worldwide with dementia have tended to apply a uniform age-specific prevalence, assuming no important geographic variation.6, 7 Prevalence has been noted to be lower in developing countries,8 strikingly so in some studies.9, 10
Alzheimer's Disease International, the umbrella organisation for national Alzheimer's associations, convened an international group of experts to generate up-to-date evidence-based estimates for the prevalence and numbers of people with dementia in all regions of the world. Such figures would provide an authoritative and consistent foundation for global policymaking, and would assist national Alzheimer's associations to raise awareness of the size of the challenge faced by this and future generations.
Section snippets
Study design
We selected a Delphi consensus approach, guided by a systematic review of the published work on the prevalence of dementia from around the world. The essence of the Delphi consensus method is to derive quantitative estimates through the qualitative assessment of evidence. Studies of widely different design and quality can be assessed, much more than is usual in systematic reviews. When published information is scarce, experts can make inferences using other data from comparable contexts.
Results
Figure 1 shows the extent of the global research evidence on the prevalence of dementia. The world regions coloured in red (North America, Europe, Japan, and Australia) are well covered with several studies of good methodological quality. Some epidemiological studies have been done in the regions coloured in pink, but they are insufficient in quality or quantity to provide representative estimates of the regional prevalence of dementia. Regions marked in white are completely or almost
Discussion
We have generated expert consensus estimates of age-specific dementia prevalence for different world regions using the Delphi technique. We estimate that 24 million people have dementia today and that this amount will double every 20 years to 42 million by 2020 and 81 million by 2040, assuming no changes in mortality, and no effective prevention strategies or curative treatments. Of those with dementia, 60% live in developing countries, with this number rising to 71% by 2040. The rate of
References (27)
- et al.
Hemoglobin levels and Alzheimer disease: an epidemiologic study in India
Am J Geriatr Psychiatry
(2004) World Health Report 2003—Shaping the future
(2003)- Comas-Herrera A, Wittenberg R, Pickard L, Knapp M, MRC-CFAS. Cognitive impairment in older people: its implications for...
- et al.
EUROCARE: a cross-national study of co-resident spouse carers for people with Alzheimer's disease: I—factors associated with carer burden
Int J Geriatr Psychiatry
(1999) Care arrangements for people with dementia in developing countries
Int J Geriatr Psychiatry
(2004)- et al.
National estimates of the quantity and cost of informal caregiving for the elderly with dementia
J Gen Intern Med
(2001) The need for research on dementia in developing countries
Trop Med Health
(1997)- et al.
The magnitude of dementia occurrence in the world
Alzheimer Dis Assoc Disord
(2004) Methodological issues in population-based research into dementia in developing countries: a position paper from the 10/66 Dementia Research Group
Int J Geriatr Psychiatry
(2000)- et al.
Prevalence of Alzheimer's disease and other dementias in rural India: the Indo-US study
Neurology
(1998)
Prevalence of Alzheimer's disease and dementia in two communities: Nigerian Africans and African Americans
Am J Psychiatry
Consensus methods for medical and health services research
BMJ
Consensus development methods, and their use in clinical guideline development
Health Technol Assess
Cited by (4331)
Gut instincts: Unveiling the connection between gut microbiota and Alzheimer's disease
2024, Clinical Nutrition ESPENMagnesium ions and dementia
2024, Journal of NeurorestoratologyMetabolomics and Risk of Dementia: A Systematic Review of Prospective Studies
2024, Journal of NutritionThe amyloid-β peptide: Guilty as charged?
2024, Biochimica et Biophysica Acta - Molecular Basis of Disease