ABSTRACT: Objective Aims to observe temporal change in dementia prevalence, identify factors related to regional diversity of dementia subtype and propose explanatory hypothesis.
Method : Studies qualifying selection criteria were chosen after PubMedline search, to identify prevalence of all dementia, Alzheimer´s disease (AD) and vascular dementia (VaD) and to compare those analytically with related data.
Result : 1) There has been temporal change of dementia prevalence in Far-eastern countries more prevalent VaD (before year 1989), mutually contradictory reports (1990 1994)-more prevalent VaD in Japan, more prevalent AD in Korea and China-, more prevalent AD (after 1995). 2) Dementia prevalence in Africa seems relatively low and AD is more prevalent than VaD. 3) Reports from India are mutually contradictory; more prevalent VaD, more prevalent AD. 4) Reports from America and Europe have been consistent that AD is more prevalent as previously reported.
Conclusion : Author´s hypothesis is as follows. It may be hard to find dementia case in a society until average life expectancy reaches to the threshold age of dementia. Once it is over the threshold age, incidence of dementia may upsurge in a short period. High incidence-high mortality society may last for a while. With the efforts to control risk factors of dementia and improve medical services, incidence and mortality of dementia may gradually decline to reach low incidence-low mortality society at the end. The transition from high incidence-high mortality society to low incidence-low mortality society may develop in various ways according to social health policies and efforts to control risk factors of dementia and improve medical services.
The reason why dementia case was not found in Nigcria is because average life expectancy in Nigeria was not reached to the threshold age of dementia. The reasons why VaD is less prevalent than AD in Far-eastern countries are mainly due to low incidence of VaD in Japan, but mainly due to high mortality of VaD in Korea and China. Namely, japan is closer to the low incidence-low mortality society than Korea and China.
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