Prevalence of dementia in the developing world substantially underestimated
28 July 2008
As the average age of the global population increases, dementia and other age-related illnesses are increasing in prevalence. Recent estimates have suggested that over 24 million people live with dementia worldwide, with 4.6m new cases every year. However, a number of studies have suggested that the prevalence of dementia in the developing world is between a quarter and a fifth of that typically recorded in developed countries.
Now, research announced at the International Conference on Alzheimer's Disease and published online today in the journal The Lancet suggests that this figure has been underestimated and that levels of dementia in the developing world may be much closer to those in the developed world.
The research was conducted by the 10/66 Dementia Research Group, an international collaboration whose funders include the Wellcome Trust. The 10/66 Dementia Research Group is part of Alzheimer's Disease International. The group is so named because less than one tenth of all population-based dementia research has been directed towards the two-thirds or more of all people with dementia who live in developing parts of the world. It aims to provide by far the most extensive source of information regarding dementia in low- and middle-income countries.
Professor Martin Prince from the Institute of Psychiatry, King's College London, who leads the group, believes that a number of factors may have led to researchers failing to identify a significant proportion of cases of dementia.
"It's likely that cultural differences may be partly responsible for researchers missing cases of dementia," says Professor Prince. "Our evidence suggests that relatives in developing world countries are less likely to perceive or report that their elders are experiencing difficulties, even in the presence of clear evidence of disability and memory impairment."
The research group assessed almost 15 000 people over the age of 65 in 11 countries, including India, China, Cuba and Peru. The assessment consisted of interviews with the participant and, typically, a family member, as well as a physical examination and a blood test. The criteria used by the 10/66 researchers were developed and validated cross-culturally across Latin America, Africa, South and South-east Asia in an attempt to enable valid comparisons to be made between different countries and cultures even when a high proportion of older people had received little or no education.
According to the study, prevalence of dementia in urban settings in Latin America is comparable with rates in Europe and the US, though the prevalence in China and India is lower.
Dementia leads to associated disability, such as memory impairment, affecting the quality of life of the patient. However, pilot studies carried out by the group suggest that dementia also places a high burden on the carer and that this is exacerbated by lack of knowledge of the disease and its likely progression.
"You could question the point of labelling someone as having dementia if their relatives do not acknowledge it as a problem," says Professor Prince. "Our data suggest that even if it is not recognised as dementia, the illness places a heavy burden on both the elderly patient and their relatives. Being able to estimate accurately the true population of people living with burden is the first important step towards putting into place appropriate health and social care systems."
The 10/66 investigators are now analysing their data to examine the burden and impact of dementia in different countries, relative to that of other chronic diseases. This will include the effect of dementia on disability, dependency, strain on the carer, and the economic cost of dementia and other diseases. These data, in conjunction with the prevalence estimates now published, will enable policymakers in low-income and middle-income countries to prioritise more effectively, as they begin to invest more heavily in the prevention and control of chronic non-communicable diseases.
The research has been welcomed by Marc Wortmann, Executive Director of Alzheimer's Disease International, which supports the 10/66 Dementia Research Group.
“Behind every case of dementia, there are relatives who are also affected, and both patients and carers need support," says Mr Wortmann. "Alzheimer’s Disease International hopes that the World Health Organisation will use these findings to make raising awareness of and tackling dementia a priority in all parts of the world."
Image: Heidi Cartwright; Wellcome Images
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Wellcome Trust
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Notes for editors
1. Llibre Rodriguez, J et al. Prevalence of dementia in Latin America, India, and China: a population-based cross-sectional survey. The Lancet, published online in advance 28 July 2008.
2. The 10/66 Dementia Research Group is a collective of researchers carrying out population-based research into dementia, non-communicable diseases and ageing in low- and middle-income countries. 10/66 refers to the two-thirds (66 per cent) of people with dementia living in low- and middle-income countries, and the ten per cent or less of population-based research that has been carried out in those regions. 10/66 is a part of Alzheimer's Disease International, and is coordinated from the Institute of Psychiatry, King's College London.
The study was funded by the Wellcome Trust Health Consequences of Population Change Programme, the US Alzheimer’s Association, and Fondo Nacional De Ciencia Y Tecnologia, Consejo De Desarrollo Cientifico Y Humanistico, and Universidad Central De Venezuela. Alzheimer’s Disease International provided support for networking and infrastructure.
3. The Wellcome Trust is the largest charity in the UK. It funds innovative biomedical research, in the UK and internationally, spending over £600 million each year to support the brightest scientists with the best ideas. The Wellcome Trust supports public debate about biomedical research and its impact on health and wellbeing.
4. King’s College London is one of the top 25 universities in the world (Times Higher 2007) and the fourth oldest in England. A research-led university based in the heart of London, King's has 19 700 students from more than 140 countries, and 5400 employees. King's has an outstanding reputation for providing world-class teaching and cutting-edge research. The College is in the top group of UK universities for research earnings and has an annual income of approximately £400m. An investment of £500m has been made in the redevelopment of its estate.
5. Alzheimer’s Disease International (ADI) is the international federation of 77 Alzheimer associations around the world. It was founded in 1984 as a global network for Alzheimer associations to share and exchange information, resources and skills.