Conventional estimates of dementia incidence in middle-income countries have been too optimistic, suggests one of the largest studies of dementia incidence to date, published Online First in The Lancet. New estimates generated using a cross-culturally validated algorithm that is sensitive to more mild to moderate cases indicate that dementia incidence in middle-income 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.
"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", explains Martin Prince from King's College London who led the research. "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.
A recently developed alternative approach to diagnosing dementia (the 10/66 Dementia Diagnosis) that uses methods developed and validated in 25 low- and middle–income countries, 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 1.5.5 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."
In a linked Comment, Kathleen Hall and Hugh Hendrie from Indiana University School of Medicine in the USA say: "The most vexing question posed by Prince and colleagues is that, if the link is substantial, why is incidence of dementia not higher in middle-income countries and even higher in low-income countries than in the high-income countries? One explanation they suggest is that the high case mortality associated with dementia in middle-income countries results in an underestimate of incident cases. [But there is another possible explanation]…that low education may simply be a marker for socioeconomic deprivation including poverty, malnutrition, and toxic environmental exposures…These factors, incidentally, have also been implicated as risk factors for dementia."
For Professor Martin Prince, Institute of Psychiatry, King's College London, London, UK please contact Seil Collins, Press Office, King's College London T) +44 (0)207 848 5377 or +44 (0)797 972 8674 E) seil.collins@kcl.ac.uk
For Dr Kathleen Hall, Indiana University School of Medicine, Indianapolis, IN, USA. Please contact Mary Hardin IU Communications T) +1 317 274 7722 E) mhardin@iu.edu
Notes to editors:
*Quote direct from authors and cannot be found in text of Article
** For such individuals, and in settings where awareness of dementia is low, it may be difficult to assess the impact of dementia on the lives of older people in the early stages of the disease. This is the likeliest explanation for the lower incidence according to DSM-IV and similar dementia criteria.
Journal
The Lancet