Burden of disease due to dementia in the elderly population of Korea: present and future

DALYs due to dementia were calculated using various epidemiologic data such as incidence, prevalence, remission rate, case mortality, age of onset, disease duration, disability weight, total mortality of the population, and population structure. All the data were derived from various epidemiologic studies conducted in Korea and from a Korean national dataset [19]. This previous nationwide population study carried out in 2008 was based on 8,199 probability-sampled Koreans aged 65 years or older. The study used a 2-step assessment method to identify persons with dementia: 1) All the sampled individuals were invited to participate in the Phase I screening assessment using the Mini-Mental State Examination via door-to-door home visits, and 2) the Phase II diagnostic assessment for dementia was administered using the Korean version of the Consortium to Establish a Registry for Alzheimer’s Disease Assessment Packet (CERAD-K) clinical assessment battery, neuroimaging, including computed tomography or magnetic resonance imaging (MRI), and laboratory testing. Patients were diagnosed with dementia using the criteria established in the Diagnostic and Statistical Manual, 4th Revision (DSM-IV), or with Alzheimer’s disease according to the criteria of the National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer’s Disease and Related Disorders Association (NINCDS-ADRDA), or with vascular dementia according to the criteria of the National Institute of Neurologic Disorders and Stroke/Association Internationale pour la Recherche et l’Enseignement en Neurosciences (NINDS-AIREN) [19]. We adopted gender- and age-specific prevalence of dementia for this study from the published article [19] and report [20]. As the previous report used a sample aged 65 years or older, we also adopted the prevalence of dementia in adults aged 65 years or older. Case mortality due to dementia and total mortality of the population by gender and age group were derived from cause of death statistics from Statistics Korea [21]. In Korea, the cause of death on the death certificate must, by law, be decided by a doctor. Therefore, Korea has a relatively comprehensive and accurate death certification system. The population structure of each gender and age group in 2008 was derived from baseline population estimates from Statistics Korea [16]. These datasets from Statistics Korea are public data sources and completely open to the public with free website access [16, 21]. Other parameters for the estimation of the burden of disease, including incidence, disease duration, and age of onset, were estimated with DISMOD-II software [22], using prevalence, remission rate, case mortality, total population, and total mortality. DISMOD II, developed by WHO for the GBD project, is a software program that can be used to estimate missing parameters and to verify the consistency of the estimates for diseases [23]. The remission rate was assumed to be zero. The disability weight of 0.911 was derived from the results in the previous Korean panel study [24].

In general, this study followed the protocols of the original GBD study [25]. DALYs are the sum of two components. The first, Years of Life Lost (YLLs), measures the number of years lost when a person dies prematurely. The second component, Years Lived with Disability measures the number of years of healthy life lost due to temporary or permanent disability. YLL estimates were derived from mortality and life expectancy at birth in 2008 [26]. YLD estimates were derived from incidence, mortality, disease duration, and age of onset from the DISMOD II output. YLL, YLD and DALY estimates were calculated according to gender and 5-year age groups. We forecasted the DALYs due to dementia in the years 2010–2050 by applying demographic structure projections and assuming a constant age-specific prevalence of dementia [27].

Input variables in the DISMOD II model (prevalence, dementia mortality, remission rate, population and overall mortality) and output variables in the year 2008 generated from the model are illustrated in Table 1. Comparing input and output variables in terms of prevalence we did not find any discrepancies; this implies consistency of estimates for the diseases. Incidence demonstrated its peak at the ages of 80–84 and subsequently decreased. Case mortality showed a gradually increasing pattern in both genders. Incidence, prevalence, mortality, duration, and age of onset outputs shown in Table 1 were used in the YLD calculation. Mortality due to dementia from the DISMOD II output was used in the YLL calculation.

YLLs, YLDs, and DALYs in the year 2008 due to dementia in the elderly in Korea were 24,344, 232,303, and 256,647 person-years, respectively (Table 2). The burden of dementia was highest in the age group of 65–69 years (Table 2, Figure 1). YLLs, YLDs, and DALYs due to dementia were calculated per 100,000 in each age group and are listed in Table 2 and Figure 2. In total, the YLLs, YLDs, and DALYs in 2008 due to dementia per 100,000 were 50, 478, and 528 person-years, respectively. When projected to the general population, the burden of disease due to dementia per 100,000 was 435 person-years in males and 622 person-years in females in 2008. In the population aged 65 years or older, the burden of dementia was 5,117 person-years per 100,000 (males: 5,228 person-years, females: 5,041 person-years) in 2008.

DALYs due to dementia projected from the years 2010 to 2050 are illustrated in Figure 3. In both males and females, DALYs due to dementia were expected to show a continuous increase. In 2050, DALYs due to dementia (814,629 person-years) are expected to be 3.0 times higher than those in the year 2010 (274,849 person-years).