Worldwide prevalence and incidence of dementia.

Dementia is a common and disabling disorder in the elderly. Because of the worldwide aging phenomenon, existing in both developed and developing countries, dementia has a growing public health relevance. This article reviews the prevalence and incidence data for dementia reported in the international literature in the last 10 years. Results from 36 prevalence and 15 incidence studies have been examined. Prevalence is equal to 0.3 to 1.0 per 100 people in individuals aged 60 to 64 years, and increases to 42.3 to 68.3 per 100 people in individuals 95 years and older. The incidence varies from 0.8 to 4.0 per 1,000 person years in people aged 60 to 64 years, and increases to 49.8 to 135.7 per 1,000 person years when the population was older than 95 years. The international comparison allows the following conclusions: (i) both prevalence and incidence show little geographical variation, as differences between countries seem to reflect methodological rather than real differences [the low prevalence of dementia in Africa needs to be confirmed by incidence data]; (ii) both incidence and prevalence figures increase with age even in the advanced ages; (iii) regarding dementia types, most of the inconsistency in results from different studies is due to vascular dementia rather than to Alzheimer's disease (AD); (iv) it is still unclear if the reported higher frequency of vascular dementia in Asian populations is due to differential distribution of genetic and/or environmental factors, or due to methodological differences; (v) different dementia types might have different age distributions.