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Prevalence of dementia and major dementia subtypes in the Chinese populations: A meta-analysis of dementia prevalence surveys, 1980–2010
Journal of Clinical Neuroscience 19 (2012) 1333–1337
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Review
Prevalence of dementia and major dementia subtypes in the Chinese populations: A meta-analysis of dementia prevalence surveys, 1980–2010 Yaodong Zhang, Yong Xu ⇑, Hongwei Nie, Ting Lei, Yan Wu, Ling Zhang, Minjie Zhang School of Radiation Medicine and Public Health, Soochow University, 199 Ren ai Road, Suzhou Industrial Park, Suzhou 215123, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 12 January 2011 Accepted 28 January 2012
Keywords: Alzheimer’s disease (AD) China Dementia Meta analysis Vascular dementia (VaD)
a b s t r a c t The aim of this study was to determine the prevalence of dementia and its major subtypes in China. Forty-eight eligible studies were included in this review. The pooled prevalence for the population aged 60 years and older of Alzheimer’s disease (AD) was 1.9%, vascular dementia (VaD) was 0.9%, and total dementia was 3.0%. The prevalence of VaD was significantly higher in Northern China than in Southern China. The prevalence of VaD was significantly higher in urban compared to rural areas. The prevalence of dementia and prevalence of AD increased with age in both males and females, and a higher prevalence of AD than VaD was observed in all age groups. AD has become more common than VaD in China since 1990. The current prevalence of dementia in China may be similar to that of developed countries. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction By the end of 2008, the elderly Chinese population, aged 60 years of age and above, had reached 159.89 million, accounting for 12% of the total Chinese population. This age group is predicted to reach 457 million by 2050. With this rapid growth in the elderly Chinese population, the prevention and treatment of age-related chronic diseases is of growing importance. Dementia is a disease of particular concern because the decline in memory and other cognitive functions that characterize this condition also lead to a loss of independent function that has a wide-ranging impact on individuals, families, and healthcare systems. An accurate national estimate of the prevalence of dementia is essential for effective planning for long-term care and medical costs that will fall on the social security system Medicare, and other insurance programs for elderly adults in China. The aim of the present study was to perform a systematic analysis of published epidemiological studies on the prevalence of dementia in the elderly Chinese population from 1980 to 2010. 2. Literature search The databases used in this meta-analysis [Chongqing VIP (1989–), CNKI (1979–), CBMDISK (1980–), and MEDLINE (1966–)] were inclusive up to October 2009. The core search terms used ⇑ Corresponding author. Tel.: +86 0512 65880072; fax: +86 0512 65880052. E-mail address: [email protected] (Y. Xu). 0967-5868/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jocn.2012.01.029
were ‘‘dementia’’, ‘‘Alzheimer’s disease’’ (AD), ‘‘vascular dementia’’ (VaD), ‘‘epidemiological survey’’, and ‘‘prevalence’’. When possible, the authors of the included studies were contacted to ascertain their knowledge of unpublished data. The present study includes epidemiological studies in the Hong Kong area. 3. Inclusion criteria All included studies met the following four selection criteria: (i) case collections were based on field surveys; (ii) studies were based on population samples; (iii) case collections were conducted in two stages: screening and diagnostic phases; and (iv) all samples were screened with brief cognitive tests, such as the Mini Mental State Examination, the Hasegawa Dementia scale, or the Blessed Dementia Scale. Those who were screen positive were scored below a given cutoff point on one or two screening tests, or were clinically suspected of dementia. Those patients with suspected dementia were examined further by senior physicians with the aid of laboratory tests, clinical features, and neuropsychological tests. Clinical diagnostic criteria employed in the 48 studies included the Diagnostic and Statistical Manual of Mental Disorders, Third Edition. The International Statistical Classification of Diseases 10th Revision and the National Institute of Neurological and Communicative Disorders and Stroke/The Alzheimer’s Disease and Related Disorders Association were used to diagnose possible and probable AD. The Hachinski–Ischemia Score and National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l’Enseignement en Neurosciences were used to differentiate AD and VaD.
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4. Data extraction Two observers assessed the eligibility of the studies independently. Disagreements between the reviewers were resolved through discussion. Data were extracted by the same reviewers using a standardized data extraction form created for the present study and with help from others as needed. The following data were obtained from each study: first author’s name, journal and year of publication, place of study, and prevalence data. The authors of primary studies were asked to check the accuracy of extracted data and to supply additional data if required. Forty-eight characteristics of the prevalence of dementia were included in the present study. 5. Data analysis All meta-analyses were analyzed using Comprehensive Meta Analysis, a software package developed by BioStat International (Tampa, FL, USA). 6. Results The search strategy identified 73 articles. After the obviously irrelevant abstracts were removed, the full texts of the remaining 66 studies were obtained. Forty-eight articles satisfied all inclusion criteria (Table 1). Twenty-five articles were excluded mainly because they were not original descriptions of population prevalence. The 48 selected studies covered 21 provinces and municipalities in China. A total elderly population of 105,866 was investigated, and 2,920 patients with dementia were detected. Among these patients, those with AD numbered 1,830 whereas those with VaD accounted for 905. The combined result for the pooled prevalence in the elderly population was 3.0% (95% confidence interval [CI], 2.4– 3.9%) for dementia, 1.9% (95% CI, 1.4–2.4%) for AD, and 0.9% (95% CI, 0.6–1.1%) for VaD. 7. Chronological prevalence of dementia Data were classified into five groups (Table 2) based on the study years. The prevalence of dementia increased markedly from 1.3% in 1985–1990 to 3.9% in 2001–2005, but decreased slightly in 2006–2010. The prevalence of AD showed an almost identical tendency in 1985–2000. In 2006–2010, AD prevalence was 2.3%, equal to that in 2001–2005. The prevalence of VaD increased considerably from 0.4% in 1991–1995 to 1.1% in 2001–2005, but decreased in 2006–2010. 8. Prevalence of dementia with respect to age The prevalence of dementia increased with age, from 1.0% of those aged 60–64 years to 26.3% of those aged 85 and older (Table 3). The prevalence of AD increased with age in both males and females. The result shows that the prevalence of AD in females was higher than in males in every age group. The prevalence of VaD increased from those aged 65–69 years to the group aged 85 years and older. A higher prevalence of AD than VaD was observed in all age groups. 9. Prevalence of dementia in different regions The prevalence of dementia was analyzed in different regions to determine the geographical characteristics of this disease in China (Table 4). The prevalence of AD was slightly higher in Northern than in Southern China, whereas that of VaD was markedly higher in Northern than in Southern China. The prevalence of AD was
slightly higher in rural China than in the city, whereas that of VaD was significantly higher in urban than in rural China. 10. Discussion Forty-eight eligible studies, published between 1980 and 2010, were included in the current meta-analysis. A total elderly Chinese population of 105,866 was investigated, and 2,920 patients with dementia were detected. Among these patients, those with AD numbered 1,830, whereas VaD accounted for 905. The proportions of AD and VaD were 62.8% and 30.9%, respectively. The combined pooled prevalence in the elderly population aged 60 years and older was 3.0% for dementia; 1.9% for AD; and 0.9% for VaD. A higher prevalence of AD than VaD was observed in all age groups and across all regions. The pooled prevalence of dementia in the elderly population aged 65 years and older was 6.0%, slightly lower than that reported in developed countries.49 This inconsistency may be caused by the population sampling methods (including variations in detection and diagnosis), or real geographical variations. For example, the apolipoprotein E4 allele, which is a well-known risk factor for dementia in Caucasians50 and Chinese populations,51–53 has a higher proportion in western countries than in China.54–57 However, China’s first multi-center, large sample study of dementia,44 which used standard criteria and selection processes for the cases diagnosed, has shown that the prevalence of senile dementia and the distribution of dementia subtypes are similar to those reported in Western countries. Three reports58–60 on dementia in China have shown that the incidence of dementia and AD is similar to that in Western countries. These results indicate that the current prevalence of dementia in China may be similar to that in western countries. The pooled prevalence of VaD was significantly higher in Northern than in Southern China. There are different exposures to risk factors, including hypertension, high salt diet, alcohol, and cigarette consumption, between Southern and Northern China. Vascular risk factors increase the risk of VaD, which may explain the north–south regional variation in the prevalence of VaD. There are no consistent conclusions on the differences in the prevalence of dementia between rural and urban China. Considering that the average life expectancy in rural China is lower than that in urban China, the prevalence of dementia in rural areas may be lower than in their urban counterparts. The notably lower educational level of the rural elderly compared with that of the urban elderly may lead to a higher prevalence of dementia in rural China than in urban China. However, the present study shows that the pooled prevalence of dementia and VaD are significantly higher in the cities than in the rural areas. Several factors, including environmental and lifestyle factors, may explain this difference. Suh et al.61 compared the prevalence of VaD and AD in numerous countries and found that AD was more prevalent than VaD in USA and Europe. However, in Asian countries before 1989, VaD was more prevalent than AD (China, Korea and Japan); AD has become nearly twice as prevalent as VaD since the early 1990s.The present study shows that a higher prevalence of AD than VaD is observed in all age groups and in different regions. Thus, the major subtype of dementia in China is AD, not VaD, and is similar to the prevalence in developed countries. Moreover, the present study found that VaD accounts for 30.9% and AD for 62.8% of patients with dementia. These figures are similar to the findings reported in Europe, North America, and Africa. The present findings indicate that the prevalence of dementia and AD increased significantly with age in China. However, the prevalence did not double almost every five years, in contrast to the findings in the international literature.62,63 The prevalence of VaD increased moderately from the age of 60 years to 65 years in China. The current study shows that the prevalence of dementia
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Y. Zhang et al. / Journal of Clinical Neuroscience 19 (2012) 1333–1337 Table 1 Forty-eight studies of the prevalence of dementia included in this review Yearref
Study design
Chen et al., 19871 Zhang et al., 19892 Chen et al., 19923 Mao et al., 19934 Gao et al., 19935 Gao et al., 19946 Liu et al., 19957 Wang et al., 19958 Liu et al., 19969 Wu et al., 199610 Li et al., 199711 Tang et al., 199812 Zhu et al., 199813 Lu et al., 199814 Yu et al., 199815 Li et al., 199816 Chiu et al., 199817 Wang et al., 199918 Tang et al., 199919 Li et al., 199920 Zhao et al., 200021 Fan et al., 200022 Xie et al., 200023 Lai et al., 200024 Zhang et al., 200025 Fei et al., 200126 Sun et al., 200127 Zhang et al., 200128 Tang et al., 200129 Zhu et al., 200130 Zhou et al., 200131 Qu et al., 200132 Tang et al., 200233 Jiang et al., 200234 Zou et al., 200235 Shen et al., 200236 Li et al., 200337 Liang et al., 200338 Qu et al., 200439 Gao et al., 200440 Yu et al., 200441 Chen et al., 200442 Yuan et al., 200543 Zhang et al., 200544 Tang et al., 200745 Tan et al., 200746 Huang et al., 200747 Yan et al., 200848
Prevalence (%) A
Location
Age
Beijing Shanghai Beijing Fujian Shanghai Hunan Taiwan Shanghai Taiwan Hainan Guangdong Beijing Shanghai Zhejiang Guangdong Taian Hong Kong Anhui Sichuan Beijing Shandong Jiangsu Beijing Guangdong Shanghai Shanghai Liaoning Beijing Sichuan Shandong shanghai Shanxi Beijing Guangdong Chongqing Shandong Inner Mongolia Guangdong Shanxi Guangdong Hebe Hainan Jiangxi Four areas Guangdong Hubei Guizhou Beijing
P60 P60 P60 P60 P60 P60 P65 P55 P65 P60 P65 P60 P55 P60 P65 P65 P70 P65 P65 P60 P65 P60 P60 P75 P55 P55 P60 P55 P55 P60 P55 P55 P60 P60 P65 P60 60 60 55 60 65 60 60 55 55 55 60 65
No. subjects(male/female)
Urban/rural
AD
VaD
Dementia
8,740 (4.055/4.685) 5,055 5,172 (2.385/2.787) 1,982 3,779 5,125 5,297 (2.753/2.544) 1,515 1,016 2,528 (1.103/1.425) 505 504(210/294) 3,083(1.304/1.779) 1,689 (863/866) 1.018 2,915 11,034 2,749 (998/1.751) 5,987 (2.653/3.334) 1,027 (372/655 2,186 (2.114/72) 3,268 1,491 3,825 1,186 (597/589) 462 (216/246) 2,000 (884/1116) 5,743 5,353 2,014 (1758/256) 15,910 4,807 (2.040/2.810) 2,788 (1.356/1.482) 1,524 (715/809) 1,519 (<11/908) 2,038 (886/1.152) 2,324 (1.846/478) 1,418 (599/819) 4,850 1,839 (1.727/1.112) 2,674 (1.630/1.044) 12,628 2,126 (1.042/1.084) 34,807 5,276 3,908 3,299 (1.227/2.002) 1,160 (499/661)
U U U U+R U U U R R U+R R U U U R U U U+R R U U U+R U U U U U U+R U+R U U+R U+R U U U R U U U+R U U U+R U U U+R U+R U U
0.4 (0.3–0.5) 2.0 (1.7–2.5) 0.2 (0.1–0.4) 1.5 (1.0–2.1) 3.1 (2.6–3.8) 0.6 (0.5–0.9) 0.3 (0.2–0.5) 1.8 (1.2–2.6) 2.2 (1.4–3.3) 0.4 (0.2–0.8) 5.0 (3.4–7.2) 2.0 (1.1–3.6) 3.6 (3.0–4.3) 6.0 (4.9–7.2) 4.7 (3.6–6.2) 2.0 (1.5–2.6) 0.5(0.4–0.7) 4.0 (3.3–4.80) 1.4 (1.2–1.8) 3.7 (2.7–5.0) 3.7 (2.7–5.0)
0.7 (0.6–0.9) 0.8 (0.6–1.1) 0.5 (0.3–0.7) 1.1 (0.7–1.7) 1.1 (0.8–1.4) 0.2 (0.1–0.4) 0.2 (0.1–0.4) 0.3(0.1–0.7) 1.1 (0.6–1.9) 0.1 (0.0–0.3)
1.0 0.9 0.9 0.3 1.0 0.2 2.4 2.4
(0.6–1.6) (0.5–1.7) (0.6–1.3) (0.2–0.4) (0.7–1.4) (0.1–0.3) (1.7–3.6) (1.7–3.6)
1.7 5.0 0.9 1.5 2.4 2.2 2.1 2.8 2.2 2.1 5.0 3.1 4.8 0.8 1.3 3.6
(1.2–2.5) (4.3–5.7) (0.5–1.7) (0.7–3.1) (1.8–3.2) (1.8–2.6) (1.7–2.5) (2.2–3.7) (1.9–2.4) (1.7–2.5) (4.3–5.9) (2.4–4.2) (3.8–6.0) (0.5–1.3) (0.9–1.9) (2.7–4.7)
1.2 0.6 0.4 2.2 4.6 1.6 0.4 1.3 0.6 1.1 1.5 1.3 0.6 0.3 1.3 1.0
(0.8–1.9) (0.4–0.9) (0.2–1.0) (1.2–4.0) (3.7–5.6) (1.3–1.9) (0.2–0.6) (0.3–1.9) (0.5–0.8) (0.9–1.5) (1.1–2.1) (0.8–2.0) (0.3–1.1) (0.1–0.7) (0.9–1.9) (0.6–1.7)
1.3 3.3 0.3 3.4 2.1 2.4 2.0 1.2 2.0
(0.8–1.9) (2.6–4.0) (0.2–0.4) (2.7–4.2) (2.0–2.3) (2.0–2.9) (1.6–2.5) (0.9–1.7) (1.3–3.0)
2.2 1.8 0.4 0.7 0.8 0.9 0.5 0.5 1.9
(1.6–3.0) (1.4–2.4) (0.3–0.6) (0.4–1.1) (0.8–0.9) (0.6–1.1) (0.3–0.7) (0.3–0.9) (1.3–2.9)
1.3 3.1 0.8 2.9 4.2 0.9 0.6 2.2 4.4 0.6 5.9 5.2 5.6 7.0 3.6 3.1 0.9 5.3 1.7 6.1 6.1 1.3 3.6 5.7 2.8 3.7 9.0 4.6 2.5 4.2 3.0 3.6 7.5 5.2 5.7 1.1 2.7 4.6 2.1 3.8 5.8 0.7 4.2
(1.1–1.5) (2.7–3.7) (0.6–0.1) (2.3–3.8) (3.6–4.9) (0.6–1.2) (0.4–0.8) (1.6–3.0) (3.3–5.9) (0.4–1.0) (4.2–8.4) (3.5–7.5) (4.8–6.4) (5.9–8.4) (2.8–4.6) (2.5–3.8) (0.7–1.1) (4.5–6.2) (1.4–2.1) (4.8–7.8) (4.8–7.8) (1.0–1.8) (2.8–4.7) (5.0–5.5) (2.0–3.9) (2.3–5.8) (7.8–10.3) (4.1–5.1) (2.1–2.9) (3.4–5.1) (2.8–3.3) (3.1–4.1) (6.5–8.5) (4.2–6.5) (4.7–7.0) (0.8–1.7) (2.1–3.4) (3.6–5.8) (1.7–2.5) (3.0–4.7) (5.0–6.7) (0.6–0.9) (3.4–5.1)
3.5 2.7 1.9 4.1
(3.0–4.0) (2.2–3.3) (1.5–2.5) (3.1–5.4)
3.2 (2.0–5.1)
AD = Alzheimer’s disease, R = rural, U = urban, VaD = vascular dementia. A Age in years.
Table 2 The chronological prevalence (and 95% confidence interval) of dementia in China Dementia
Alzheimer’s disease
Vascular dementia
Year/s
No. subjects
Population
Prevalence
No. subjects
Population
Prevalence
No. subjects
Population
Prevalence
1985–90 1991–95 1996–00 2001–05 2006–10
112 364 1020 1413 397
8740 22870 39110 38667 11145
1.3 1.4 2.9 3.9 3.6
34 236 579 870 270
8740 22870 35842 38667 11145
0.4 0.9 2.0 2.3 2.3
65 112 225 423 100
8740 22870 35340 38667 11145
0.7 0.4 0.7 1.1 0.9
(1.1–1.5) (0.6–3.2) (1.9–4.5) (2.8–5.6) (2.5–5.2)
and AD is higher in women than in men within the same age category, similar to that reported by Meng et al.64 This observation is consistent with the results of two meta-analyses.63,65 However, in the Kungsholmen Project66 in Sweden, there were no observed sex differences found in AD prevalence among those under the age of 85 years. No gender differences were found in VaD prevalence in China.
(0.3–0.5) (0.4–2.0) (1.2–3.2) (1.6–3.3) (1.5–3.6)
(0.6–0.9) (0.2–0.8) (0.4–1.3) (0.7–1.7) (0.6–1.5)
The chronological prevalence of AD and dementia increased significantly from 1980 to 2005. Similarly, an observational study from Hisayama, Japan, demonstrated that the prevalence of all causes of dementia significantly increased from 1985 to 2005 and that a similar trend was observed for AD but not for VaD.67 The chronological prevalence of dementia in China can be explained by several factors. The reform policy in China adopted
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Table 3 The prevalence of dementia (%) with respect to population age in China from 1985 to 2010 AgeA
Alzheimer’s disease Male
60–64 65–69 70–74 75–79 80–84 P85 A
0.4 0.5 1.4 6.6 10.2 10.5
(0.1–3.5) (0.1–1.8) (0.2–7.8) (1.8–21.6) (6.0–16.8) (4.4–22.8)
Vascular dementia
Total dementia
Female
Total
Male
Female
Total
Male
0.5 1.2 3.5 5.9 15.3 34.0
0.5 0.7 2.7 5.5 14.0 29.0
0.7 0.5 0.7 0.8 0.7 2.2
0.8 0.2 0.2 0.6 1.0 1.7
0.4 0.4 0.5 0.7 1.0 2.0
1.0 1.8 2.9 9.9 16.7 32.1
(0.1–0.51) (0.7–1.7) (2.3–5.3) (3.9–8.9) (8.2–26.7) (21.8–44.1)
(0.1–4.1) (0.3–1.4) (1.6–4.6) (3.5–8.5) (10.5–18.4) (16.1–31.5)
(0.0–10.4) (0.0–11.6) (0.0–24.2) (0.0–23.7) (0.0–9.2) (0.0–59.8)
(0.1–5.6) (0.0–0.9) (0.0–1.7) (0.0–15.8) (0.0–24.7) (0.0–45.3)
(0.1–2.5) (0.0–4.6) (0.0–10.2) (0.0–19.1) (0.0–19.2) (0.0–54.1)
(0.5–1.9) (1.1–3.0) (1.7––4.9) (6.015.8) (6.4–36.9) (18.4–49.8)
Female
Total
1.2 1.5 3.8 11.9 18.2 18.8
1.0 1.3 3.1 9.3 19.7 26.3
(0.5–2.8) (0.4–6.1) (1.6–8.9) (7.6–18.2) (13..6–22.6) (15.4–22.6)
(0.6–1.8) (0.8–2.0) (1.9–4.8) (7.2–11.8) (16.3–23.7) (11.8–48.7)
Age in years.
Table 4 The prevalence (%) of dementia in different regions in China from 1985 to 2010 Residence
Alzheimer’s disease
Vascular dementia
Dementia
Urban Rural Northern China Southern China Total
1.8 1.9 1.9 1.8 1.9
0.9 0.4 1.2 0.6 0.9
3.2 2.6 3.9 2.9 3.0
(1.3–2.4) (1.0–3.3) (1.3–2.7) (1.3–2.6) (1.4–2.4)
(0.4–1.3) (0.2–0.9) (0.8–1.8) (0.5–0.8) (0.6–1.1)
(2.4–4.2) (1.4–4.7) (2.8–5.5) (1.9–3.6) (2.4–3.9)
30 years ago has evoked rapid social and economic changes, including dietary and lifestyle changes as well as changes in vascular risk factors.68 These changes could increase the risk of AD because vascular risk factors have been linked to AD. Furthermore, the change could also be caused by an increased incidence of AD in elderly Chinese. As the incidence of AD rises steeply with age, the number of patients with AD will increase as the population ages. Li et al.69 reported that the incidence rates of dementia in Beijing were slightly higher than those 10 years ago by conducting a similar epidemiological survey in the same district of Beijing. In addition, the rapid increase may be caused by improvement in the diagnosis of dementia. However, Tang et al.70 reported that the prevalence of AD and VaD remained stable during a given period after conducting a similar epidemiological survey in the same district of Chengdu. The limitations of the present study should be noted. First, as pronounced results are more likely to be published, publication bias cannot be excluded. Second, given that limited information could be obtained from some included studies, relevant detailed statistical analyses could not be performed. Conflict of interest/disclosures The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication. References 1. Chen XS, Zhang JZ, Jiang ZN. Epidemiological study of mental disorders in the aged in the urban district of Beijing. Chin J Neurol Psychiatry 1987;20:145–9. 2. Zhang MY, Qu GY, Katzman R, et al. A study on dementia and Alzheimer disease. Shanghai Arch Psychiatry 1989;7:153–60. 3. Chen CH, Shin YC, Li SR. An epidemiological survey of dementia in Xicheng district, Beijing. Chin Mental Health J 1992;6:49–52. 4. Mao RH, Zhang RR, Ni YX. Prevalence of senile dementia in urban and rural areas of Luoyang. Chin J Gerontol 1993;3:226–8. 5. Gao ZX, Liu FG, Yan H. An epidemiological study of dementia. Shanghai Arch Psychiatry 1993;5:21–2. 6. Gao ZS, Shang XQ, Shan FB. An epidemiological survey in human province. Human Med J 1994;8:11–4. 7. Liu HC, Lin KN, Ting EL, et al. Prevalence and subtypes of dementia in Taiwan, a community survey of 5297 individuals. J Am Geriatr Soc 1995;43:144–9. 8. Wang D, Bu SM. A survey of prevalence of dementia in Shanghai. Shanghai Arch Psychiatry 1995;7:76–8. 9. Liu CK, Lin RT, Chen YF, et al. Prevalence of dementia in an urban area in Taiwan. J Formos Med Assoc 1996;95:762–8.
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Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Review
Prevalence of dementia and major dementia subtypes in the Chinese populations: A meta-analysis of dementia prevalence surveys, 1980–2010 Yaodong Zhang, Yong Xu ⇑, Hongwei Nie, Ting Lei, Yan Wu, Ling Zhang, Minjie Zhang School of Radiation Medicine and Public Health, Soochow University, 199 Ren ai Road, Suzhou Industrial Park, Suzhou 215123, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 12 January 2011 Accepted 28 January 2012
Keywords: Alzheimer’s disease (AD) China Dementia Meta analysis Vascular dementia (VaD)
a b s t r a c t The aim of this study was to determine the prevalence of dementia and its major subtypes in China. Forty-eight eligible studies were included in this review. The pooled prevalence for the population aged 60 years and older of Alzheimer’s disease (AD) was 1.9%, vascular dementia (VaD) was 0.9%, and total dementia was 3.0%. The prevalence of VaD was significantly higher in Northern China than in Southern China. The prevalence of VaD was significantly higher in urban compared to rural areas. The prevalence of dementia and prevalence of AD increased with age in both males and females, and a higher prevalence of AD than VaD was observed in all age groups. AD has become more common than VaD in China since 1990. The current prevalence of dementia in China may be similar to that of developed countries. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction By the end of 2008, the elderly Chinese population, aged 60 years of age and above, had reached 159.89 million, accounting for 12% of the total Chinese population. This age group is predicted to reach 457 million by 2050. With this rapid growth in the elderly Chinese population, the prevention and treatment of age-related chronic diseases is of growing importance. Dementia is a disease of particular concern because the decline in memory and other cognitive functions that characterize this condition also lead to a loss of independent function that has a wide-ranging impact on individuals, families, and healthcare systems. An accurate national estimate of the prevalence of dementia is essential for effective planning for long-term care and medical costs that will fall on the social security system Medicare, and other insurance programs for elderly adults in China. The aim of the present study was to perform a systematic analysis of published epidemiological studies on the prevalence of dementia in the elderly Chinese population from 1980 to 2010. 2. Literature search The databases used in this meta-analysis [Chongqing VIP (1989–), CNKI (1979–), CBMDISK (1980–), and MEDLINE (1966–)] were inclusive up to October 2009. The core search terms used ⇑ Corresponding author. Tel.: +86 0512 65880072; fax: +86 0512 65880052. E-mail address: [email protected] (Y. Xu). 0967-5868/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jocn.2012.01.029
were ‘‘dementia’’, ‘‘Alzheimer’s disease’’ (AD), ‘‘vascular dementia’’ (VaD), ‘‘epidemiological survey’’, and ‘‘prevalence’’. When possible, the authors of the included studies were contacted to ascertain their knowledge of unpublished data. The present study includes epidemiological studies in the Hong Kong area. 3. Inclusion criteria All included studies met the following four selection criteria: (i) case collections were based on field surveys; (ii) studies were based on population samples; (iii) case collections were conducted in two stages: screening and diagnostic phases; and (iv) all samples were screened with brief cognitive tests, such as the Mini Mental State Examination, the Hasegawa Dementia scale, or the Blessed Dementia Scale. Those who were screen positive were scored below a given cutoff point on one or two screening tests, or were clinically suspected of dementia. Those patients with suspected dementia were examined further by senior physicians with the aid of laboratory tests, clinical features, and neuropsychological tests. Clinical diagnostic criteria employed in the 48 studies included the Diagnostic and Statistical Manual of Mental Disorders, Third Edition. The International Statistical Classification of Diseases 10th Revision and the National Institute of Neurological and Communicative Disorders and Stroke/The Alzheimer’s Disease and Related Disorders Association were used to diagnose possible and probable AD. The Hachinski–Ischemia Score and National Institute of Neurological Disorders and Stroke-Association Internationale pour la Recherche et l’Enseignement en Neurosciences were used to differentiate AD and VaD.
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4. Data extraction Two observers assessed the eligibility of the studies independently. Disagreements between the reviewers were resolved through discussion. Data were extracted by the same reviewers using a standardized data extraction form created for the present study and with help from others as needed. The following data were obtained from each study: first author’s name, journal and year of publication, place of study, and prevalence data. The authors of primary studies were asked to check the accuracy of extracted data and to supply additional data if required. Forty-eight characteristics of the prevalence of dementia were included in the present study. 5. Data analysis All meta-analyses were analyzed using Comprehensive Meta Analysis, a software package developed by BioStat International (Tampa, FL, USA). 6. Results The search strategy identified 73 articles. After the obviously irrelevant abstracts were removed, the full texts of the remaining 66 studies were obtained. Forty-eight articles satisfied all inclusion criteria (Table 1). Twenty-five articles were excluded mainly because they were not original descriptions of population prevalence. The 48 selected studies covered 21 provinces and municipalities in China. A total elderly population of 105,866 was investigated, and 2,920 patients with dementia were detected. Among these patients, those with AD numbered 1,830 whereas those with VaD accounted for 905. The combined result for the pooled prevalence in the elderly population was 3.0% (95% confidence interval [CI], 2.4– 3.9%) for dementia, 1.9% (95% CI, 1.4–2.4%) for AD, and 0.9% (95% CI, 0.6–1.1%) for VaD. 7. Chronological prevalence of dementia Data were classified into five groups (Table 2) based on the study years. The prevalence of dementia increased markedly from 1.3% in 1985–1990 to 3.9% in 2001–2005, but decreased slightly in 2006–2010. The prevalence of AD showed an almost identical tendency in 1985–2000. In 2006–2010, AD prevalence was 2.3%, equal to that in 2001–2005. The prevalence of VaD increased considerably from 0.4% in 1991–1995 to 1.1% in 2001–2005, but decreased in 2006–2010. 8. Prevalence of dementia with respect to age The prevalence of dementia increased with age, from 1.0% of those aged 60–64 years to 26.3% of those aged 85 and older (Table 3). The prevalence of AD increased with age in both males and females. The result shows that the prevalence of AD in females was higher than in males in every age group. The prevalence of VaD increased from those aged 65–69 years to the group aged 85 years and older. A higher prevalence of AD than VaD was observed in all age groups. 9. Prevalence of dementia in different regions The prevalence of dementia was analyzed in different regions to determine the geographical characteristics of this disease in China (Table 4). The prevalence of AD was slightly higher in Northern than in Southern China, whereas that of VaD was markedly higher in Northern than in Southern China. The prevalence of AD was
slightly higher in rural China than in the city, whereas that of VaD was significantly higher in urban than in rural China. 10. Discussion Forty-eight eligible studies, published between 1980 and 2010, were included in the current meta-analysis. A total elderly Chinese population of 105,866 was investigated, and 2,920 patients with dementia were detected. Among these patients, those with AD numbered 1,830, whereas VaD accounted for 905. The proportions of AD and VaD were 62.8% and 30.9%, respectively. The combined pooled prevalence in the elderly population aged 60 years and older was 3.0% for dementia; 1.9% for AD; and 0.9% for VaD. A higher prevalence of AD than VaD was observed in all age groups and across all regions. The pooled prevalence of dementia in the elderly population aged 65 years and older was 6.0%, slightly lower than that reported in developed countries.49 This inconsistency may be caused by the population sampling methods (including variations in detection and diagnosis), or real geographical variations. For example, the apolipoprotein E4 allele, which is a well-known risk factor for dementia in Caucasians50 and Chinese populations,51–53 has a higher proportion in western countries than in China.54–57 However, China’s first multi-center, large sample study of dementia,44 which used standard criteria and selection processes for the cases diagnosed, has shown that the prevalence of senile dementia and the distribution of dementia subtypes are similar to those reported in Western countries. Three reports58–60 on dementia in China have shown that the incidence of dementia and AD is similar to that in Western countries. These results indicate that the current prevalence of dementia in China may be similar to that in western countries. The pooled prevalence of VaD was significantly higher in Northern than in Southern China. There are different exposures to risk factors, including hypertension, high salt diet, alcohol, and cigarette consumption, between Southern and Northern China. Vascular risk factors increase the risk of VaD, which may explain the north–south regional variation in the prevalence of VaD. There are no consistent conclusions on the differences in the prevalence of dementia between rural and urban China. Considering that the average life expectancy in rural China is lower than that in urban China, the prevalence of dementia in rural areas may be lower than in their urban counterparts. The notably lower educational level of the rural elderly compared with that of the urban elderly may lead to a higher prevalence of dementia in rural China than in urban China. However, the present study shows that the pooled prevalence of dementia and VaD are significantly higher in the cities than in the rural areas. Several factors, including environmental and lifestyle factors, may explain this difference. Suh et al.61 compared the prevalence of VaD and AD in numerous countries and found that AD was more prevalent than VaD in USA and Europe. However, in Asian countries before 1989, VaD was more prevalent than AD (China, Korea and Japan); AD has become nearly twice as prevalent as VaD since the early 1990s.The present study shows that a higher prevalence of AD than VaD is observed in all age groups and in different regions. Thus, the major subtype of dementia in China is AD, not VaD, and is similar to the prevalence in developed countries. Moreover, the present study found that VaD accounts for 30.9% and AD for 62.8% of patients with dementia. These figures are similar to the findings reported in Europe, North America, and Africa. The present findings indicate that the prevalence of dementia and AD increased significantly with age in China. However, the prevalence did not double almost every five years, in contrast to the findings in the international literature.62,63 The prevalence of VaD increased moderately from the age of 60 years to 65 years in China. The current study shows that the prevalence of dementia
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Y. Zhang et al. / Journal of Clinical Neuroscience 19 (2012) 1333–1337 Table 1 Forty-eight studies of the prevalence of dementia included in this review Yearref
Study design
Chen et al., 19871 Zhang et al., 19892 Chen et al., 19923 Mao et al., 19934 Gao et al., 19935 Gao et al., 19946 Liu et al., 19957 Wang et al., 19958 Liu et al., 19969 Wu et al., 199610 Li et al., 199711 Tang et al., 199812 Zhu et al., 199813 Lu et al., 199814 Yu et al., 199815 Li et al., 199816 Chiu et al., 199817 Wang et al., 199918 Tang et al., 199919 Li et al., 199920 Zhao et al., 200021 Fan et al., 200022 Xie et al., 200023 Lai et al., 200024 Zhang et al., 200025 Fei et al., 200126 Sun et al., 200127 Zhang et al., 200128 Tang et al., 200129 Zhu et al., 200130 Zhou et al., 200131 Qu et al., 200132 Tang et al., 200233 Jiang et al., 200234 Zou et al., 200235 Shen et al., 200236 Li et al., 200337 Liang et al., 200338 Qu et al., 200439 Gao et al., 200440 Yu et al., 200441 Chen et al., 200442 Yuan et al., 200543 Zhang et al., 200544 Tang et al., 200745 Tan et al., 200746 Huang et al., 200747 Yan et al., 200848
Prevalence (%) A
Location
Age
Beijing Shanghai Beijing Fujian Shanghai Hunan Taiwan Shanghai Taiwan Hainan Guangdong Beijing Shanghai Zhejiang Guangdong Taian Hong Kong Anhui Sichuan Beijing Shandong Jiangsu Beijing Guangdong Shanghai Shanghai Liaoning Beijing Sichuan Shandong shanghai Shanxi Beijing Guangdong Chongqing Shandong Inner Mongolia Guangdong Shanxi Guangdong Hebe Hainan Jiangxi Four areas Guangdong Hubei Guizhou Beijing
P60 P60 P60 P60 P60 P60 P65 P55 P65 P60 P65 P60 P55 P60 P65 P65 P70 P65 P65 P60 P65 P60 P60 P75 P55 P55 P60 P55 P55 P60 P55 P55 P60 P60 P65 P60 60 60 55 60 65 60 60 55 55 55 60 65
No. subjects(male/female)
Urban/rural
AD
VaD
Dementia
8,740 (4.055/4.685) 5,055 5,172 (2.385/2.787) 1,982 3,779 5,125 5,297 (2.753/2.544) 1,515 1,016 2,528 (1.103/1.425) 505 504(210/294) 3,083(1.304/1.779) 1,689 (863/866) 1.018 2,915 11,034 2,749 (998/1.751) 5,987 (2.653/3.334) 1,027 (372/655 2,186 (2.114/72) 3,268 1,491 3,825 1,186 (597/589) 462 (216/246) 2,000 (884/1116) 5,743 5,353 2,014 (1758/256) 15,910 4,807 (2.040/2.810) 2,788 (1.356/1.482) 1,524 (715/809) 1,519 (<11/908) 2,038 (886/1.152) 2,324 (1.846/478) 1,418 (599/819) 4,850 1,839 (1.727/1.112) 2,674 (1.630/1.044) 12,628 2,126 (1.042/1.084) 34,807 5,276 3,908 3,299 (1.227/2.002) 1,160 (499/661)
U U U U+R U U U R R U+R R U U U R U U U+R R U U U+R U U U U U U+R U+R U U+R U+R U U U R U U U+R U U U+R U U U+R U+R U U
0.4 (0.3–0.5) 2.0 (1.7–2.5) 0.2 (0.1–0.4) 1.5 (1.0–2.1) 3.1 (2.6–3.8) 0.6 (0.5–0.9) 0.3 (0.2–0.5) 1.8 (1.2–2.6) 2.2 (1.4–3.3) 0.4 (0.2–0.8) 5.0 (3.4–7.2) 2.0 (1.1–3.6) 3.6 (3.0–4.3) 6.0 (4.9–7.2) 4.7 (3.6–6.2) 2.0 (1.5–2.6) 0.5(0.4–0.7) 4.0 (3.3–4.80) 1.4 (1.2–1.8) 3.7 (2.7–5.0) 3.7 (2.7–5.0)
0.7 (0.6–0.9) 0.8 (0.6–1.1) 0.5 (0.3–0.7) 1.1 (0.7–1.7) 1.1 (0.8–1.4) 0.2 (0.1–0.4) 0.2 (0.1–0.4) 0.3(0.1–0.7) 1.1 (0.6–1.9) 0.1 (0.0–0.3)
1.0 0.9 0.9 0.3 1.0 0.2 2.4 2.4
(0.6–1.6) (0.5–1.7) (0.6–1.3) (0.2–0.4) (0.7–1.4) (0.1–0.3) (1.7–3.6) (1.7–3.6)
1.7 5.0 0.9 1.5 2.4 2.2 2.1 2.8 2.2 2.1 5.0 3.1 4.8 0.8 1.3 3.6
(1.2–2.5) (4.3–5.7) (0.5–1.7) (0.7–3.1) (1.8–3.2) (1.8–2.6) (1.7–2.5) (2.2–3.7) (1.9–2.4) (1.7–2.5) (4.3–5.9) (2.4–4.2) (3.8–6.0) (0.5–1.3) (0.9–1.9) (2.7–4.7)
1.2 0.6 0.4 2.2 4.6 1.6 0.4 1.3 0.6 1.1 1.5 1.3 0.6 0.3 1.3 1.0
(0.8–1.9) (0.4–0.9) (0.2–1.0) (1.2–4.0) (3.7–5.6) (1.3–1.9) (0.2–0.6) (0.3–1.9) (0.5–0.8) (0.9–1.5) (1.1–2.1) (0.8–2.0) (0.3–1.1) (0.1–0.7) (0.9–1.9) (0.6–1.7)
1.3 3.3 0.3 3.4 2.1 2.4 2.0 1.2 2.0
(0.8–1.9) (2.6–4.0) (0.2–0.4) (2.7–4.2) (2.0–2.3) (2.0–2.9) (1.6–2.5) (0.9–1.7) (1.3–3.0)
2.2 1.8 0.4 0.7 0.8 0.9 0.5 0.5 1.9
(1.6–3.0) (1.4–2.4) (0.3–0.6) (0.4–1.1) (0.8–0.9) (0.6–1.1) (0.3–0.7) (0.3–0.9) (1.3–2.9)
1.3 3.1 0.8 2.9 4.2 0.9 0.6 2.2 4.4 0.6 5.9 5.2 5.6 7.0 3.6 3.1 0.9 5.3 1.7 6.1 6.1 1.3 3.6 5.7 2.8 3.7 9.0 4.6 2.5 4.2 3.0 3.6 7.5 5.2 5.7 1.1 2.7 4.6 2.1 3.8 5.8 0.7 4.2
(1.1–1.5) (2.7–3.7) (0.6–0.1) (2.3–3.8) (3.6–4.9) (0.6–1.2) (0.4–0.8) (1.6–3.0) (3.3–5.9) (0.4–1.0) (4.2–8.4) (3.5–7.5) (4.8–6.4) (5.9–8.4) (2.8–4.6) (2.5–3.8) (0.7–1.1) (4.5–6.2) (1.4–2.1) (4.8–7.8) (4.8–7.8) (1.0–1.8) (2.8–4.7) (5.0–5.5) (2.0–3.9) (2.3–5.8) (7.8–10.3) (4.1–5.1) (2.1–2.9) (3.4–5.1) (2.8–3.3) (3.1–4.1) (6.5–8.5) (4.2–6.5) (4.7–7.0) (0.8–1.7) (2.1–3.4) (3.6–5.8) (1.7–2.5) (3.0–4.7) (5.0–6.7) (0.6–0.9) (3.4–5.1)
3.5 2.7 1.9 4.1
(3.0–4.0) (2.2–3.3) (1.5–2.5) (3.1–5.4)
3.2 (2.0–5.1)
AD = Alzheimer’s disease, R = rural, U = urban, VaD = vascular dementia. A Age in years.
Table 2 The chronological prevalence (and 95% confidence interval) of dementia in China Dementia
Alzheimer’s disease
Vascular dementia
Year/s
No. subjects
Population
Prevalence
No. subjects
Population
Prevalence
No. subjects
Population
Prevalence
1985–90 1991–95 1996–00 2001–05 2006–10
112 364 1020 1413 397
8740 22870 39110 38667 11145
1.3 1.4 2.9 3.9 3.6
34 236 579 870 270
8740 22870 35842 38667 11145
0.4 0.9 2.0 2.3 2.3
65 112 225 423 100
8740 22870 35340 38667 11145
0.7 0.4 0.7 1.1 0.9
(1.1–1.5) (0.6–3.2) (1.9–4.5) (2.8–5.6) (2.5–5.2)
and AD is higher in women than in men within the same age category, similar to that reported by Meng et al.64 This observation is consistent with the results of two meta-analyses.63,65 However, in the Kungsholmen Project66 in Sweden, there were no observed sex differences found in AD prevalence among those under the age of 85 years. No gender differences were found in VaD prevalence in China.
(0.3–0.5) (0.4–2.0) (1.2–3.2) (1.6–3.3) (1.5–3.6)
(0.6–0.9) (0.2–0.8) (0.4–1.3) (0.7–1.7) (0.6–1.5)
The chronological prevalence of AD and dementia increased significantly from 1980 to 2005. Similarly, an observational study from Hisayama, Japan, demonstrated that the prevalence of all causes of dementia significantly increased from 1985 to 2005 and that a similar trend was observed for AD but not for VaD.67 The chronological prevalence of dementia in China can be explained by several factors. The reform policy in China adopted
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Table 3 The prevalence of dementia (%) with respect to population age in China from 1985 to 2010 AgeA
Alzheimer’s disease Male
60–64 65–69 70–74 75–79 80–84 P85 A
0.4 0.5 1.4 6.6 10.2 10.5
(0.1–3.5) (0.1–1.8) (0.2–7.8) (1.8–21.6) (6.0–16.8) (4.4–22.8)
Vascular dementia
Total dementia
Female
Total
Male
Female
Total
Male
0.5 1.2 3.5 5.9 15.3 34.0
0.5 0.7 2.7 5.5 14.0 29.0
0.7 0.5 0.7 0.8 0.7 2.2
0.8 0.2 0.2 0.6 1.0 1.7
0.4 0.4 0.5 0.7 1.0 2.0
1.0 1.8 2.9 9.9 16.7 32.1
(0.1–0.51) (0.7–1.7) (2.3–5.3) (3.9–8.9) (8.2–26.7) (21.8–44.1)
(0.1–4.1) (0.3–1.4) (1.6–4.6) (3.5–8.5) (10.5–18.4) (16.1–31.5)
(0.0–10.4) (0.0–11.6) (0.0–24.2) (0.0–23.7) (0.0–9.2) (0.0–59.8)
(0.1–5.6) (0.0–0.9) (0.0–1.7) (0.0–15.8) (0.0–24.7) (0.0–45.3)
(0.1–2.5) (0.0–4.6) (0.0–10.2) (0.0–19.1) (0.0–19.2) (0.0–54.1)
(0.5–1.9) (1.1–3.0) (1.7––4.9) (6.015.8) (6.4–36.9) (18.4–49.8)
Female
Total
1.2 1.5 3.8 11.9 18.2 18.8
1.0 1.3 3.1 9.3 19.7 26.3
(0.5–2.8) (0.4–6.1) (1.6–8.9) (7.6–18.2) (13..6–22.6) (15.4–22.6)
(0.6–1.8) (0.8–2.0) (1.9–4.8) (7.2–11.8) (16.3–23.7) (11.8–48.7)
Age in years.
Table 4 The prevalence (%) of dementia in different regions in China from 1985 to 2010 Residence
Alzheimer’s disease
Vascular dementia
Dementia
Urban Rural Northern China Southern China Total
1.8 1.9 1.9 1.8 1.9
0.9 0.4 1.2 0.6 0.9
3.2 2.6 3.9 2.9 3.0
(1.3–2.4) (1.0–3.3) (1.3–2.7) (1.3–2.6) (1.4–2.4)
(0.4–1.3) (0.2–0.9) (0.8–1.8) (0.5–0.8) (0.6–1.1)
(2.4–4.2) (1.4–4.7) (2.8–5.5) (1.9–3.6) (2.4–3.9)
30 years ago has evoked rapid social and economic changes, including dietary and lifestyle changes as well as changes in vascular risk factors.68 These changes could increase the risk of AD because vascular risk factors have been linked to AD. Furthermore, the change could also be caused by an increased incidence of AD in elderly Chinese. As the incidence of AD rises steeply with age, the number of patients with AD will increase as the population ages. Li et al.69 reported that the incidence rates of dementia in Beijing were slightly higher than those 10 years ago by conducting a similar epidemiological survey in the same district of Beijing. In addition, the rapid increase may be caused by improvement in the diagnosis of dementia. However, Tang et al.70 reported that the prevalence of AD and VaD remained stable during a given period after conducting a similar epidemiological survey in the same district of Chengdu. The limitations of the present study should be noted. First, as pronounced results are more likely to be published, publication bias cannot be excluded. Second, given that limited information could be obtained from some included studies, relevant detailed statistical analyses could not be performed. Conflict of interest/disclosures The authors declare that they have no financial or other conflicts of interest in relation to this research and its publication. References 1. Chen XS, Zhang JZ, Jiang ZN. Epidemiological study of mental disorders in the aged in the urban district of Beijing. Chin J Neurol Psychiatry 1987;20:145–9. 2. Zhang MY, Qu GY, Katzman R, et al. A study on dementia and Alzheimer disease. Shanghai Arch Psychiatry 1989;7:153–60. 3. Chen CH, Shin YC, Li SR. An epidemiological survey of dementia in Xicheng district, Beijing. Chin Mental Health J 1992;6:49–52. 4. Mao RH, Zhang RR, Ni YX. Prevalence of senile dementia in urban and rural areas of Luoyang. Chin J Gerontol 1993;3:226–8. 5. Gao ZX, Liu FG, Yan H. An epidemiological study of dementia. Shanghai Arch Psychiatry 1993;5:21–2. 6. Gao ZS, Shang XQ, Shan FB. An epidemiological survey in human province. Human Med J 1994;8:11–4. 7. Liu HC, Lin KN, Ting EL, et al. Prevalence and subtypes of dementia in Taiwan, a community survey of 5297 individuals. J Am Geriatr Soc 1995;43:144–9. 8. Wang D, Bu SM. A survey of prevalence of dementia in Shanghai. Shanghai Arch Psychiatry 1995;7:76–8. 9. Liu CK, Lin RT, Chen YF, et al. Prevalence of dementia in an urban area in Taiwan. J Formos Med Assoc 1996;95:762–8.
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