In low- and middle-income countries, mild cognitive impairment—an intermediate state between normal signs of cognitive aging, such as becoming increasingly forgetful, and dementia, which may or may not progress—is consistently associated with higher disability and with neuropsychiatric symptoms but not with most socio-demographic factors, according to a large study published in this week's PLoS Medicine.
The established 10/66 Dementia Research Group interviewed approximately 15 000 people over 65 years of age who did not have dementia in eight low- and middle-incomes countries: Cuba, Dominican Republic, Peru, Mexico, Venezuela, Puerto Rico, China, and India.
Participants also completed standardized assessments of their mental and physical health and cognitive function and the researchers also interviewed relatives and carers for further details about any memory loss or other declines in cognitive function or the presence of any neuropsychiatric symptoms.
Then, using a clinical framework and a statistical model, the authors found that mild cognitive impairment with related memory problems was associated with disability, anxiety, apathy, and irritability but not with depression.
Increasing age or former education level did not seem to be linked but the authors found that men had a slightly higher prevalence of mild cognitive impairment than women. Furthermore, the prevalence of this type of mild cognitive impairment ranged from 0.8% in China to 4.3% in India.
The authors say: "This is one of the first studies, to our knowledge, to investigate the prevalence of [mild cognitive impairment with related memory problems] in [low- and middle-income countries], where the large majority of older people and people with dementia currently live."
They continue: "Differences in prevalence between countries were marked and ranged from 0.8% (China) to 4.3% (India), that is, greater than fivefold variation. After direct standardization for age, gender, and education, using the whole population as the reference, these differences were not markedly attenuated."
The authors conclude: "Further evaluation is needed of the associations with disability and neuropsychiatric symptoms since our findings do suggest higher than expected comorbidity and there are large absolute numbers of older people with [mild cognitive impairment with related memory problems] in these rapidly ageing and populous world regions."
Funding: The 10/66 Dementia Research Group population based surveys were supported by: the Wellcome Trust (UK) (GR066133); the World Health Organization; the US Alzheimer's Association (IIRG – 04 – 1286); and the Fondo Nacional de Ciencia Y Tecnologia, Consejo de Desarrollo Cientifico Y Humanistico, Universidad Central de Venezuela (Venezuela). RS is funded by the NIHR Specialist Biomedical Research Centre for Mental Health at the South London and Maudsley NHS Foundation Trust and Institute of Psychiatry, King's College London. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The 10/66 Dementia Research Group (DRG) works closely with Alzheimer's Disease International (ADI), the non-profit federation of 77 Alzheimer associations around the world. ADI is committed to strengthening Alzheimer associations worldwide, raising awareness regarding dementia and Alzheimer's disease, and advocating for more and better services for people with dementia and their caregivers. ADI is supported in part by grants from GlaxoSmithKline, Novartis, Lundbeck, Pfizer, and Eisai. Concerning the relationship with ADI, the 10/66 Dementia Research Group is an autonomous research network administered from the Institute of Psychiatry, King's College London. Its relationship with Alzheimer's Disease International is primarily around research dissemination; the 10/66 project website is hosted on the ADI server, and the cost of developing the site was met by ADI. 10/66 routinely makes a report of ongoing projects to the ADI Council, and have provided training at ADI's Alzheimer Universities. 10/66 have not received funding from ADI to conduct research, and ADI has no influence upon or input into 10/66 published research outputs. Martin Prince (but not the 10/66 DRG per se), through IoP/ KCL has received three small grants from ADI to fund researchers based at IoP/ KCL to work on the 2009, 2010, and 2011 World Alzheimer reports (not part of the present study). MD is a paid statistical reviewer for PLoS Medicine. All other authors have declared that no competing interests exist.
Citation: Sosa AL, Albanese E, Stephan BCM, Dewey M, Acosta D, et al. (2012) Prevalence, Distribution, and Impact of Mild Cognitive Impairment in Latin America, China, and India: A 10/66 Population-Based Study. PLoS Med 9(2): e1001170. doi:10.1371/journal.pmed.1001170
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