10% of Older People Suffer Dementia, Another 20% Exhibit Mild Cognitive Impairment
One in three people over 65 in the US exhibit either dementia or mild cognitive impairment. There is a great need for treatments that target the mechanisms of aging, particularly those that contribute to the environment of chronic inflammation that characterizes the aging brain. Neurodegenerative conditions are the outcome of so many different contributing mechanisms that success in the medical control of aging, finding ways to repair or work around the cell and tissue damage that causes aging, seems the most plausible path towards anything that resembles either a cure or absolute prevention.
Dementia is a highly prevalent condition characterized by cognitive difficulties that typically begin in adulthood and affect a person's ability to independently perform everyday activities. Alzheimer's disease is the most common cause of dementia, accounting for approximately 60% to 80% of all dementia cases. Mild cognitive impairment (MCI) is a clinical classification assigned to people who are thought to be transitioning between normal aging and dementia. Because age is the most potent risk factor for dementia and MCI, the number of adults with these conditions is projected to rise dramatically in the US and around the world due to demographic trends that have transformed populations from mostly young adults to mostly older adults.
Based on a community cohort of older adults in Chicago, Illinois, the prevalence of dementia due to Alzheimer's disease in the US in 2021 was estimated at 11.3% of those 65 years and older, which translates to about 6.2 million adults. Other recent estimates have been somewhat lower, likely related to differences in study methods. Similarly, different implementation of MCI criteria and cohort characteristics drive variability in MCI prevalence and rates of progression to dementia across cohorts. It is well established that annual progression rates of MCI to dementia in population- or community-based studies are lower (4% to 15%) than in clinic-based studies (12% to 17%).
The Health and Retirement Study (HRS) provides a core resource for researchers who require US population-level data on dementia and MCI prevalence and incidence. The Harmonized Cognitive Assessment Protocol (HCAP) was developed to update national estimates of the prevalence of MCI and dementia in the US. Of 9,972 age-eligible HRS participants, 4,425 were randomly selected for HCAP, and 3,496 completed a comprehensive neuropsychological test battery and informant interview, none of whom were excluded.
A total of 393 individuals (10%) were classified as having dementia and 804 (22%) as having MCI. Every 5-year increase in age was associated with higher risk of dementia (weighted odds ratio, OR, 1.95 per 5-year age difference) and MCI (OR 1.17 per 5-year age difference). Each additional year of education was associated with a decrease in risk of dementia (OR 0.93 per year of school) and MCI (OR 0.94 per year of school). In conclusion, the national prevalence of dementia and MCI in 2016 found in this cross-sectional study was similar to that of other US-based studies.