A survey of 7,072 older adults in six provinces across China, with one rural and one urban community in each province, has identified 359 older adults with dementia and 328 with depression. There were only 26 participants who had doctor-diagnosed dementia reported and 26 who had doctor-diagnosed depression. Overall, 93% of dementia cases and 93% of depression were not detected.

Undetected dementia was strongly associated with low socioeconomic status such as a low educational and occupational class, and living in a rural area.

In comparison, research in high income countries has found that about 60% of older adults with dementia are not diagnosed, and generally there has not been a strong association between low socioeconomic status and undetected dementia. One factor in China’s high rate may be that most older Chinese live with their families, who may be inclined to see dementia as a normal part of aging.

http://www.eurekalert.org/pub_releases/2013-07/kcl-o9072413.php

New estimates of dementia in China

A new review of 89 studies, involving more than 340,000 participants in total, has estimated that 9.19 million people in China had dementia in 2010, of whom 5.69 million had Alzheimer’s disease. Previous studies appear to have considerably underestimated the true burden of dementia in China, largely due to limited data availability. However, this study examined a much wider range of data sources than earlier studies, including many Chinese-language reports.

Of the 340 247 participants, 6357 had Alzheimer's disease (1.87%). Of 254,367 assessed for other forms of dementia, 3543 (1.4%) had vascular dementia, frontotemporal dementia, or Lewy body dementia.

Total dementia prevalence in 1990 was 1·8% at 65-69 years, and 42·1% at age 95-99 years; in 2010, prevalence had increased to 2·6% and 60·5%, respectively.

Prevalence was higher for women than men, but didn't differ significantly between urban and rural residents.

http://www.eurekalert.org/pub_releases/2013-06/l-mco060513.php

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(2013).  Determinants for undetected dementia and late-life depression.
The British Journal of Psychiatry. 203(3), 203 - 208.

[3559] Chan, K Y., Wang W., Wu J J., Liu L., Theodoratou E., Car J., et al.
(2013).  Epidemiology of Alzheimer's disease and other forms of dementia in China, 1990–2010: a systematic review and analysis.
The Lancet. 381(9882), 2016 - 2023.