Worldwide Dementia Prevalence Underestimated
The true prevalence of dementia in developing nations may be higher than is widely believed. In the July 28 issue of The Lancet, a group called the “10/66 Dementia Research Group,” led by Martin Prince at the Institute of Psychiatry, De Crespigny Park, London, U.K., report on their ongoing large-scale study to assess dementia prevalence in low- and middle-income countries, including both rural and urban sites within India, China, Cuba, Dominican Republic, Venezuela, Mexico, and Peru. The group found that in areas of Latin America and China in particular, the occurrence of dementia was near if not equal to dementia incidences found in Europe and higher than previously estimated. The 10/66 group, based in over 20 countries throughout developing nations, is so named because though only 10 percent of population-based dementia research is carried out in low- or middle-income countries, 66 percent of individuals with dementia live there.
The large-scale 10/66 study, initially begun in 1999, aims to collect 2,000-3,000 participants over the age of 65 within each target low-income country and to have participants undergo a one-phase assessment consisting of an interview, a blood draw, and a physical examination. The study design is centered on the 10/66 group’s carefully delineated “Dementia Diagnosis,” which puts special emphasis on diagnosing dementia in individuals in culturally diverse, low-income, and low-education environments. This is in contrast to the more common Diagnostic and Statistical Manual of Medical Disorders (DSM-IV) criteria, which the group claims is “restrictive” and in low- and middle-income countries identifies only those persons with clearly evident and quite severe cases of dementia, excluding those with possibly mild or moderate forms of the illness (see Prince et al., 2007).
The arm of the study presented in this recent publication had four primary goals: assess the prevalence and severity of dementia within the selected sites, while measuring variation amongst the sites and tying that variation to environmental factors when possible; compare the 10/66 Dementia Diagnosis to the DSM-IV criteria within those sites; compare the DSM-IV data for these sites with dementia prevalence within Europe; and evaluate the consistency of the newly obtained data to regional estimates performed by the Alzheimer’s Disease Institute (ADI). In all, nearly 15,000 interviews were completed within 11 geographic areas contained in seven low- to middle-income countries.
The group’s more inclusive algorithm for diagnosing dementia shows high sensitivity and specificity of 94 percent and 97 percent, respectively. Overall, first author Juan Llibre Rodriguez and colleagues found that the occurrence of dementia as defined by their algorithm was between 5.6 percent and 11.7 percent, depending on geographic site. Prevalence of dementia by the group’s definition was greater than that calculated by DSM-IV criteria, which indicated prevalence of 0.4 percent to 6.4 percent within those same sites. Dementia was routinely lower in men than in women, and the inverse association between education and dementia was greater than the inverse association between dementia and assets. Not surprisingly, no matter which criteria were used, dementia was strongly age-dependent, and the incidence doubled every 7.5 years over age 65, which is lower than the doubling time of four to six years after age 65 seen in developed countries.
The eye-opener was that compared to the EURODEM analysis of dementia in European sites, the frequency of dementia in urban Latin America was over four-fifths of European levels, and both rural and urban sites within China were greater than half of the European numbers. Although these low-income countries provided values smaller than European levels, the widespread thinking in research circles is that values from low-income nations would be substantially less than those seen in Europe. This mindset may have advanced in part due to a 2005 ADI study which suggested a lower prevalence of dementia in undeveloped nations such as in Africa and south Asia compared to the incidence in developed nations. Llibre Rodriguez and colleagues’ findings clearly demonstrate that the occurrence of dementia is higher in these undeveloped countries than previously thought, prompting the notion that the incidence of dementia in many areas of the developing world may have been underestimated in the past. In an accompanying Lancet editorial, Eric Larson, Group Health Center for Health Studies, Seattle, Washington, and Kenneth Langa, University of Michigan, Ann Arbor, have a suggestion as to why dementia prevalence is higher than expected in developing countries. “The rising tide of late-life dementia is both a triumph of public health and an opportunity. Increased worldwide prevalence reflects gains in life expectancy, perhaps made more evident in present knowledge-based societies. Cognitive skills are probably more essential for survival—and sustain well-being better—in cities, where people are increasingly concentrated. Because the rates rise considerably in late old age, delaying the onset of functional impairment would represent true prevention—or at least compression of morbidity,” they write.
Now that the research centers have been established by the 10/66 group throughout these countries of interest, the group hopes to extend the studies to examine what environmental and cultural determinants impact these patients. The study has already collected data that will help in this effort, including information on overall health, care considerations and burden, disability, marital status, education, income, household assets, and food security. Blood samples were also collected for glucose, cholesterol, triglyceride, and albumin analysis, as well as apolipoprotein E genotyping. The group expects to obtain data from additional sites into 2009. Due to the high levels of participation and compliance demonstrated by the people in these countries, it seems quite probable that valuable research will continue to come from these largely underserved areas in order to paint a clearer picture of where dementia hits throughout the world.—Rebecca Henderson
Rebecca Henderson is a freelance writer living in Pittsburgh, Pennsylvania.
- Prince M, Ferri CP, Acosta D, Albanese E, Arizaga R, Dewey M, Gavrilova SI, Guerra M, Huang Y, Jacob KS, Krishnamoorthy ES, McKeigue P, Rodriguez JL, Salas A, Sosa AL, Sousa RM, Stewart R, Uwakwe R. The protocols for the 10/66 dementia research group population-based research programme. BMC Public Health. 2007;7:165. PubMed.
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- Llibre Rodriguez JJ, Ferri CP, Acosta D, Guerra M, Huang Y, Jacob KS, Krishnamoorthy ES, Salas A, Sosa AL, Acosta I, Dewey ME, Gaona C, Jotheeswaran AT, Li S, Rodriguez D, Rodriguez G, Kumar PS, Valhuerdi A, Prince M, . Prevalence of dementia in Latin America, India, and China: a population-based cross-sectional survey. Lancet. 2008 Aug 9;372(9637):464-74. PubMed.
- Larson EB, Langa KM. The rising tide of dementia worldwide. Lancet. 2008 Aug 9;372(9637):430-2. PubMed.
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