Summary: New evidence indicates that the likelihood of being diagnosed with cognitive impairment or dementia among U.S. adults has grown over the last two decades.
Source: Max Planck Institute
A recent analysis by researchers at the Max Planck Institute for Demographic Research and collaborators finds that the risk of cognitive impairment and dementia in the United States rose between 1996 and 2014 when prior test experience and selective mortality are taken into account.
For years, many population studies—particularly in high-income countries—reported falling rates of cognitive decline. Those conclusions often come from longitudinal surveys in which the same people repeat the same cognitive test over time. Repeated testing can generate practice effects: participants improve simply because they become familiar with the test. If practice effects are not accounted for, trends can be biased downward and mask true increases in impairment.
To address this, Mikko Myrskylä, Joanna Hale, Jutta Gampe, Neil Mehta, and Daniel Schneider re-examined trends in cognitive impairment across the United States from 1996 through 2014. Their models explicitly adjusted for prior testing experience and for selective mortality—two factors that can distort apparent prevalence trends in aging populations.
“Models that ignore prior test experience tend to suggest a decline in cognitive impairment and dementia risk over time,” says Mikko Myrskylä, Director at the Max Planck Institute for Demographic Research (MPIDR). “Once test experience is controlled for, the trend reverses and points to an increase in risk.”
Across their primary models, the prevalence of any cognitive impairment rose for both sexes. The rise was especially pronounced among older adults—those aged 85 and above—among Latinas, and among individuals with the lowest education levels. The authors note that part of the observed increase may reflect people living longer with dementia, which would raise prevalence even if incidence remained stable.
The study analyzed more than 32,000 participants drawn from the Health and Retirement Study (HRS), a nationally representative biennial panel survey of Americans aged 50 and older and their spouses. The HRS includes a modified version of the Telephone Interview for Cognitive Status (TICS-M), a standardized instrument commonly used to detect declines in cognition in large surveys.
About this dementia research article
Source:
Max Planck Institute for Demographic Research (MPIDR)
Contacts:
Silvia Leek – Max Planck Institute
Image Source:
The image is in the public domain.
Original Research:
“Trends in the Risk of Cognitive Impairment in the United States, 1996–2014” by Mikko Myrskylä, Joanna Hale, Jutta Gampe, Neil Mehta and Daniel Schneider. Epidemiology. DOI: 10.1097/EDE.0000000000001219. (Closed access)
Abstract
Trends in the Risk of Cognitive Impairment in the United States, 1996–2014
Background:
Accumulating research has suggested declines in the risk of cognitive impairment in high-income countries, but much of that evidence comes from longitudinal surveys vulnerable to practice effects from repeated testing. This study re-evaluates trends in the United States while accounting for prior test experience and selective mortality.
Methods:
Using the Health and Retirement Study, a nationally representative panel dataset, the authors included individuals aged 50 and older observed between 1996 and 2014 (n = 32,784). Cognitive impairment and dementia were classified with standard cut points on the modified Telephone Interview for Cognitive Status. Logistic regression models estimated changes in risk for any impairment and for dementia over time, adjusting for age, sex, and race/ethnicity, and comparing models with and without adjustment for practice effects and education. The study also examined heterogeneity in trends by age group, sex, race/ethnicity, and education level.
Results:
Models that did not control for testing experience indicated declines in cognitive impairment and dementia over the study period. Once practice effects were included, the pattern reversed. In the primary adjusted models, the prevalence of any cognitive impairment increased for women from 18.7% to 21.2% (annual change 0.7%, 95% CI, 0.1%–1.3%) and for men from 17.6% to 21.0% (annual change 1.0%, 95% CI, 0.5%–1.4%). For dementia, annual increases were 1.7% for women (95% CI, 0.8%–2.6%) and 2.0% for men (95% CI, 1.0%–2.9%). The upward trend would have been larger in the absence of education gains. Increases were most rapid among Latinas, the least educated groups, and the oldest age groups.
Conclusions:
When testing experience and selective mortality are taken into account, the risk of cognitive impairment rose in the United States between 1996 and 2014. The authors call for focused research to identify the drivers behind this increase and to inform public health policies aimed at prevention, early detection, and support for those living with cognitive decline.