Levels of dementia underestimated in developing countries

Conventional estimates of dementia incidence in middle-income countries have been too optimistic, suggests one of the largest studies of dementia incidence to date, led by researchers at King’s College London's Institute of Psychiatry and published online in The Lancet today. 

The findings suggest that dementia incidence in middle-income countries might be much the same as in higher-income countries. Moreover, this is the first study to demonstrate that in less developed countries, as in developed nations, education offers substantial protection against dementia.

New estimates generated using a new cross-cultural approach to diagnosing dementia that is sensitive to more mild to moderate cases (the 10/66 Dementia Diagnosis), indicate that incidence is 1.5–2.5 times higher than that calculated using standard DSM-IV criteria. 

Professor Martin Prince who coordinates the 10/66 Dementia Research Group from the IoP at King’s and led the research says: ‘Our studies provide supportive evidence for the cognitive reserve hypothesis—that better brain development can mitigate the effects of neurodegeneration in later-life. Our findings suggest that early life influences, education and learning to read and write, may be particularly important for reducing the risk of dementia in late life. We need to understand more about cognitive reserve, how to measure it, and how it is stimulated across cultures.’

Professor Prince adds: ‘The high incidence of dementia in less developed countries reminds us that we are facing a global epidemic, and there needs to be more focus on prevention.’

Previous studies using conventional western diagnostic approaches such as the Diagnostic and Statistical Manual of Mental Disorders (DSM) IV criteria, have indicated that the incidence of dementia (the number of new dementia cases over a given time) might be considerably lower in low- and middle-income countries compared with high-income countries. 

The recently developed 10/66 Dementia Diagnosis uses methods developed and validated in 25 low- and middle–income countries and has been shown to provide accurate diagnoses even in those with little or no education.

Unlike many previous studies, restricted to single sites, this research applied both the 10/66 and standard DSM-IV criteria to nearly 12,800 people aged 65 years and older, across nine rural and urban sites in Cuba, the Dominican Republic, Venezuela, Peru, Mexico, and China to compare the incidence of dementia, and to determine whether factors such as education and literacy are protective against the development of dementia. 

The new figures indicate that 10/66 dementia incidence is 1.5–2.5 times higher than that calculated using standard DSM-IV criteria. After standardisation for age, 10/66 dementia incidence was consistently similar to, or higher than, dementia incidence previously observed in European studies.

Individuals with dementia at the start of the study had a nearly three-fold greater risk of dying compared with those who were dementia-free. The findings also showed that 10/66 dementia incidence was independently associated with increased age, being female, and low education, but not with occupational attainment. 

The authors conclude: ‘The protective effects of education seem to extend to settings where many older people have little or no formal education, and literacy confers an additional independent benefit. These findings…support the notion that cognitive reserve might counter the effects of neurodegeneration later in life.’

The 10/66 Dementia Research group’s research has been funded by the Wellcome Trust Health Consequences of Population Change Programme, WHO and the US Alzheimer’s Association.