Introduction to Supplement on Multidisciplinary Perspectives on Dementia and Related Population Health Trends
Year: 2024
Type: article
Abstract: Alzheimer’s disease and Alzheimer’s-disease-related dementias (hereafter, dementia) are a set of conditions involving impaired memory and other cognitive processes that interfere with daily functioning. Like other chronic conditions, the age-specific incidence of dementia rises sharply with age (1). Worldwide, significant increases in the number of older adults living with dementia are anticipated in the coming decades—from 55.2 million in 2019 to 78 million in 2030 and 139 million in 2050 (2)—unless effective interventions or treatments that forestall the onset of dementia are developed and widely adopted (3). The prevalence of dementia is expected to increase more rapidly in low- and middle-income countries (LMICs) than in high-income countries in the coming decades (4). This growth is likely to place significant pressures on families, who provide the bulk of care in many countries, and, particularly in high-income countries, on publicly financed services. The papers in this supplemental issue are an outgrowth of the May 2023 annual meeting of the Michigan Center on the Demography of Aging’s (MiCDA) TRENDS network. TRENDS is a network of researchers working to accelerate scientific understanding of population-level changes over time in late-life disability, death, and health. The May 2023 meeting focused on updating our understanding of dementia and dementia care trends both in the United States and internationally. MiCDA and the TRENDS network are supported by a grant from the National Institute on Aging (P30AG012846). This supplemental issue is also a follow-up to a 2018 supplemental issue of the Journals of Gerontology: Series B, undertaken by MiCDA’s TRENDS network. That issue featured 6 national studies and 3 subnational studies, each focused on a unique aspect of dementia trends. Six cross-cutting themes were identified in that issue (5): (1) dementia is becoming less prevalent in the United States overall, but not for all population groups; (2) some groups of older adults in the United States have experienced declines in the number of years lived with dementia; (3) racial and socioeconomic disparities in dementia are large and not diminishing over time; (4) rising levels of educational attainment partially account for dementia trends, and more research is needed to better understand the role of cardiovascular risk factors; (5) postponing the onset of dementia is the most effective way to reduce the size of the population living with dementia; and (6) close attention to dementia measurement challenges is critical. The papers in this current supplemental issue grow our understanding of dementia and dementia care trends in 2 complementary ways: expanding our understanding of population trends in cognitive impairment and dementia from several high-income countries, and exploring trends and projections in care and related costs for older adults with dementia across high-income and middle-income countries (6–11). Two additional editorials in this issue focus on cross-cutting topics: approaches to handling practice effects in national studies of dementia trends, and current knowledge and data gaps in the study of dementia and related care trends in LMICs (12,13). Two articles in this supplement leverage national health surveys to understand population trends in cognitive impairment and dementia in high-income countries (6,7). One draws upon harmonized data from the Health and Retirement Study (HRS), the English Longitudinal Study of Aging (ELSA), and the Survey of Health, Aging and Retirement in Europe (SHARE) (6); the other uses data from the National Health and Aging Trends Study (NHATS) (7). These data resources are particularly useful for studying trends because they are drawn from sampling frames in which individuals have a known probability of being selected and participating. When used with nonresponse-adjusted sampling weights, estimates are considered nationally representative. Myrskylä and colleagues (6) provide comparative analyses using the immediate and delayed recall of a 10-word list, a harmonized measure of memory function. They examined trends in memory function among self-responding adults ages 50 and older in the United States (HRS) from 1998 to 2018, England (ELSA) from 2002 to 2018, and 11 European countries (SHARE) from 2004 to 2019. They estimated unweighted age- and gender-adjusted mixed-effects regression models as well as models with adjustments for additional sociodemographic characteristics and health behaviors. In these models, memory test scores were standardized for each country separately, so that a 1 standard deviation (SD) change could be interpreted in the context of that country as well as across countries. They explored overall trends as well as gender, age group, and educational attainment. They found that the age-adjusted 10-year improvement in average memory test score was 0.04-SD units (95% confidence interval [CI]: 0.03, 0.05) in the United States, 0.17-SD units (95% CI: 0.15, 0.19) in England, and 0.24-SD units (95% CI: 0.23, 0.25) in the SHARE countries, when restricted to a comparable period beginning in 2004 for all studies. The gap between the United States and other countries was smaller for those ages 75 years or older, ages for which memory impairment is much more prevalent. They concluded that uncovering the causes for the cross-country heterogeneity in time trends should be a priority. Freedman and Cornman (7) focused on trends in dementia prevalence, incidence, and mortality among adults in the United States ages 72 and older. Their analysis considered the 2011–2021 period, incorporating for the first time post-COVID-19 pandemic period assessments. They found that the prevalence of probable dementia declined from 11.9% in 2011 to 9.2% in 2019 and 8.2% in 2021 (3.1% average annual decline). Declines in dementia incidence were stronger for the 2011–2021 period than for the 2011–2019 period, whereas mortality among those with dementia rose sharply with the onset of the COVID-19 pandemic. Shifts in the composition of the older population accounted for a smaller fraction of the decline over the full period (28%) than over the pre-pandemic period (45%). Thus, they concluded that continued tracking of dementia prevalence, incidence, and mortality among those with and without dementia is needed to understand the long-run consequences of the pandemic. Four additional papers in this issue focus on trends and projections in care for older adults with dementia (8–11). Two are U.S.-focused, one relying on the HRS and publicly available vital statistics (8), and the other on NHATS and its linked National Study of Caregiving (NSOC) (9). One is focused on China, and one is an international comparison of China, Mexico, and India. Feng and colleagues (8) explored evolving demographic trends in the United States and how they affect the kin networks of older adults with dementia. They focused on differences by race, emphasizing inequities in both health and family resources in the United States. Using demographic models of kinship, they estimated the availability of potential caregivers and dementia prevalence among kin by race, kin type, and the age of a focal person from 2000 to 2060. They introduced a novel index called the Dementia Dependency Ratio that considers the age and kinship structure of individuals in the population. They found that in the United States, Black individuals have larger kin networks as they age, but also have more kin with dementia than White individuals. Projections suggest that racial gaps in caregiving will widen over the next 4 decades if the racial gap in dementia prevalence remains unchanged. Their findings underscore the need for attention to racial inequality in dementia prevalence rates in the United States and the value of adopting a kinship perspective in understanding dementia care. Kim and colleagues (9) focused on gaps in respite care—assistance that provides short-term relief for caregivers—in the United States by race for caregivers helping a family member or friend with dementia. Using NHATS linked with NSOC, they found overall low rates of respite care for both Black and White caregivers of older adults with dementia. In 2015, Black caregivers to older adults with dementia had a respite care use rate 11.6 percentage points lower than that of White dementia caregivers (95% CI: −16.9 to −6.4). In 2017 and 2021, the racial difference in the use of respite care was not statistically significant. The disappearance of the racial gap was attributable to an increase in the use of respite care among Black caregivers over the study period. No increase was observed for White caregivers. They concluded that, despite a reduction in the racial gap in respite care use, efforts are needed to encourage more respite among both groups of caregivers. Jin and Wu (10) projected the trend in the number of older adults in China with limitations in activities of daily living (ADLs) with and without cognitive impairment and the associated long-term care (LTC) costs over the next 20 years. They used data on adults ages 65 and older from the 2005–2018 waves of the Chinese Longitudinal Healthy Longevity Survey. They simulated the population of China and tracked the transition of older adults over the next 20 years among 4 ADL limitation–cognition categories. They incorporated data on expenditures for paid care (direct costs) and hours of care provided by children, grandchildren, and their spouses (indirect costs). Projections suggested that the percentage of older adults with ADL limitations but without cognitive impairment will rise slowly from 4.0% in 2022 to 4.3% in 2040 and the percentage with both limitations and cognitive impairment will rise from 3.5% in 2022 to 4.1% in 2040. Costs associated with family care were projected to increase from 197 billion yuan in 2022 to 1 697 billion yuan in 2040 for older adults with ADL limitations but without cognitive impairment and from 316 billion yuan in 2022 to 4 399 billion yuan in 2040 for older adults with both ADL limitations and cognitive impairment. They concluded that impending increases in cognitive impairment should be considered when projecting LTC costs. Park and colleagues (11) used data from the Gateway to Global Aging Data in China, Mexico, and India to estimate the prevalence of care needs related to ADL and instrumental activities of daily living (IADL) limitations among older adults. They then modeled associations between caregiver availability and receipt of unpaid care using logistic regression models. They observed relatively similar patterns in care need measures across countries and over time. However, the association between caregiver availability and unpaid care receipt varied across countries: Living with family members was associated with a higher probability of receiving unpaid care in China and India, but in Mexico, this association was observed only for male care recipients. The magnitude of the association between caregiver availability and unpaid care receipt also varied with the care recipient’s gender. They concluded that additional resources and evidence-based public policy are needed in LMICs to support both paid and unpaid care for older adults with dementia. Taken together, the 6 articles and 2 editorials in this issue underscore 4 cross-cutting themes and directions for future research. Memory impairment and dementia are becoming less prevalent in the United States, particularly for adults in their mid-70s or older; but declines in memory impairment appear even larger in England and Europe. Both Myrskylä et al. (6) and Freedman and Corman (7) find using different samples, age groups, and measures, that cognitive impairment is becoming less prevalent in the United States for adults in the mid-70s and older. However, Myrskylä and colleagues’ analysis provides international comparisons that facilitate the interpretation of these declines (6). They find slower improvement in the prevalence of memory impairment in the United States (and to a lesser extent in England) compared to European countries, particularly for those less than age 75. They concluded this type of pattern is consistent with comparative trends in physical health and mortality across high-income countries. Freedman and Corman (7) seek explanations for the declining trend among those 72 and older. They find that factors such as the age distribution and changing composition of educational attainment explain less of the trend between 2011 and 2021 compared to earlier time periods. The authors imply that the accelerating decline in prevalence in the 2011–2021 period is linked to the substantial increases in mortality among those with dementia that occurred with the onset of the pandemic. One issue raised by both studies is the challenge of accounting for practice effects in national studies of cognitive impairment and dementia trends. In an accompanying editorial in this issue, Freedman and Hu (12) discuss these challenges in the context of national panel studies with replenishment and particularly how the methodological considerations may differ from studies focused on individual-level changes with age. In the United States, there are racial inequities not only in dementia prevalence but in care demands on family members and in the use of caregiver services such as respite care. Continued racial inequities in dementia prevalence were evident in the United States in both Myrskylä et al. (6) and Freedman and Cornman (7). In addition, Feng et al. (8) demonstrated that Black adults in the United States are more likely than White adults to have kin with dementia and projects racial gaps in caregiving will widen over the next 4 decades. Their findings underscore the need for attention to racial inequality in dementia prevalence rates in the United States as well as how the family care context differs for minoritized groups. Kim and colleagues (9) documented that racial gaps in the United States in respite care use by dementia caregivers have narrowed, but respite care use remains underutilized. Whether barriers to use differ for Black and White dementia caregivers was not directly addressed. Together, these findings suggest that more research is needed to better understand the role of contextual factors and their role in inequities in dementia onset and related care in the United States. Models to project dementia, dementia care, and dementia costs are challenging to estimate and need more development so that sensitivity to assumptions can be assessed. Two papers in this volume focus on dementia care-related projections. Feng and colleagues (8) projected the availability of potential caregivers and dementia prevalence among kin from 2000 to 2060. They drew upon demographic models of kinship to explore how demographic trends will affect the kin networks of older adults with dementia. Jin and Wu (10) used data from adults ages 65 and older from the 2005–2018 waves of the Chinese Longitudinal Healthy Longevity Survey. They simulated the population of China and tracked transitions across 4 groups (with and without activity limitations and with and without cognitive impairment). They then used a 2-part model to project LTC costs per capita, including family care costs. Together, these models push forward our understanding of how to project the need for and costs of dementia care and the critical importance of taking into account kin and family care when assessing costs of care despite the data and methodological challenges. Yet, further development of projection models and the ability to demonstrate sensitivity to various assumptions are needed for projection models to better inform policy. There are new opportunities and challenges for studying dementia and dementia trends in LMICs. A majority of new dementia cases over the coming decades will occur in LMICs (2). However, as noted in the accompanying commentary (13), a primary challenge in designing public health and policy approaches in LMICs is the substantial data gap. Although populations in many LMICs are rapidly aging and experiencing epidemiological transitions, there is still a lack of robust population-based data to study dementia epidemiology, risk factors, and associated disability. The International Research Network of the Harmonized Cognitive Assessment Protocol (HCAP) and others are working to bridge this data gap by promoting the collection of longitudinal and population-based harmonized data globally, including in LMICs. Several new studies are underway or are in planning that together with existing HCAP studies will represent more than 75% of the world’s adults aged 65 and older. These harmonized data will offer considerable opportunity for researchers to study dementia trends globally over the years ahead. The preparation of this introduction was supported by the National Institute on Aging of the National Institutes of Health (grant number P30AG012846). The views expressed are those of the authors alone and do not represent those of their employers or the funding agency. This introduction appears as part of a supplemental issue on Multidisciplinary Perspectives on Dementia and Related Population Health Trends, which was supported by the Michigan Center on the Demography of Aging at the University of Michigan, with funding from the National Institute on Aging of the National Institutes of Health (P30AG012846). None.
Language: English
Subfield: Psychiatry and Mental health
Field: Medicine
Domain: Health Sciences
Open Access status: hybrid
Estimated APC paid: $4,628
Awards: G3003890976, G9000029081
OpenAlex ID: W4404126397