Prevalence studies of dementia in mainland china, Hong Kong and taiwan: a systematic review and meta-analysis

Abstract

Background: Many studies have considered the prevalence of dementia in mainland China, Hong Kong and Taiwan. However, area level estimates have not been produced. This study examines area differences across mainland China, Hong Kong and Taiwan adjusting for the effect of methodological factors with the aim of producing estimates of the numbers of people with dementia in these areas.

Method and findings: A search of Chinese and English databases identified 76 dementia prevalence studies based on samples drawn from mainland China, Hong Kong and Taiwan between 1980 and 2012. A pattern of significantly decreasing prevalence was observed from northern, central, southern areas of mainland China, Hong Kong and Taiwan. Area variations in dementia prevalence were not explained by differences in methodological factors (diagnostic criteria, age range, study sample size and sampling method), socioeconomic level or life expectancy between areas. The results of meta-analysis were applied to current population data to provide best estimate. Based on the DSM-IV diagnostic criteria, the total number of people aged 60 and over with dementia in mainland China, Hong Kong and Taiwan is 8.4 million (4.6%, 95% CI: 3.4, 5.8) and in northern, central and southern areas are 3.8 (5.1%, 95% CI: 4.1, 6.1), 3.2 (4.4%, 95% CI: 3.2, 5.6) and 1.2 (3.9%, 95% CI: 2.3, 5.4) million respectively. These estimates were mainly based on the studies existing in highly developed areas and potentially affected by incomplete and insufficient data.

Conclusions: The findings of this review provide a robust estimate of area differences in dementia prevalence. Application of the estimated prevalence to population data reveals the number of people with dementia is expected to double every 20 years, areas in mainland China will be facing the greatest dementia challenge.

Figure 1. Flow plot of literature search.

Figure 2. Forest plot of the prevalence studies of dementia in mainland China, Hong Kong and Taiwan.

Figure 3. Stratified prevalence by age groups and gender.

Figure 4. Estimated age-stratified prevalence by north, central, south of mainland China, Hong Kong and Taiwan (Based on DSM-IV).

^a. Age range of estimation: The estimates of three areas in mainland China started from 60 years old, which is the definition of older people in People’s Republic of China. Both Hong Kong and Taiwan are more likely to consider elderly population as people aged 65 and above since they have higher proportion of ageing population since early 1990s. Most of their prevalence studies of dementia also recruited the participants aged 65 and over. Therefore, it is more reliable and reasonable to estimate age-stratified prevalence from 65 years old.

Figure 5. Estimated number of people with dementia by age and gender.

Figure 6. Estimated numbers of people with dementia by provinces and cities.

* The province without existing study; Jilin, Tianjin, Inner Mongo, Ningxia, Qinghai, Tibet were estimated by the model of North China. Guizhou, Yunnan and Guangxi were estimated by the model of South China.