Studies have reported that countries with lower- and middle-to-average incomes have lower rates of dementia than those in the wealthiest parts of the world. These findings might occur for several reasons, such as higher life expectancies in wealthier countries, but also may be a result of under-diagnosis. A recent study published in The Lancet used an alternate criteria for dementia diagnosis to examine protective and risk factors for dementia in middle-income countries.
This alternate diagnostic criteria, known as the 10/66 criteria, was developed because may the most widely-used criteria developed in the US to assess dementia, the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), may not be applicable in lower-income countries, where older adults have comparatively lower rates of literacy and education. In fact, these lower rates of literacy and education potentially complicate the attempt to define criteria for dementia in lower-income given the cognitive reserve hypothesis. This hypothesis posits in part that education, literacy, and occupational attainment provide cognitive resources that have a protective effect against dementia.
To evaluate both the DSM-IV and 10/66 criteria for dementia, and to test the effects of cognitive reserve in lower-income countries, an international team of researchers interviewed over 12,000 older adults across a wide range of sites in lower- and middle-income countries: Cuba, the Dominican Republic, Venezuela, Peru, Mexico and China. The interviews were comprehensive clinical interviews and included questions about demographic information and personal history. The samples included participants who were diverse in terms of educational and occupational attainment, wealth, and other factors.
The 10/66 criteria led to almost twice the dementia diagnosis across the sites as did the DSM criteria, which the authors hypothesized might miss cases of mild to moderate dementia among older adults with lower levels of education, wealth and literacy. Using the 10/66 criteria, rates of dementia relative to age are similar in these lower- and middle-income countries to those in higher-income countries. Higher education, literacy, and verbal fluency were associated with lower risk of dementia. Significantly, even when controlling for education, occupational attainment, and household wealth, literacy was associated with lower rates of dementia, providing support for the cognitive reserve hypothesis.
Prince M, Acosta D, et al. Dementia incidence and mortality in middle-income countries, and associations with indicators of cognitive reserve: a 10/66 Dementia Research Group population-based research study. The Lancet; (2012). 380: 50-58.