Alzheimer’s disease (AD) is a neurodegenerative disease that leads to progressive deterioration in memory and cognitive abilities and is the most common type of dementia, which is irreversible. However, the disease can begin to develop before symptoms of dementia appear in the preclinical and prodromal stages. Identifying individuals at these stages has been difficult, and as a result, many estimates of Alzheimer’s disease typically focus on estimating the prevalence of Alzheimer’s once dementia has developed.
Due to the irreversible nature of dementia, interventions that target Alzheimer’s disease during these stages present a tremendous opportunity to mitigate the progression of Alzheimer’s disease to its most severe stage. Thus, it is critical to understand the magnitude and risk factors along the Alzheimer’s disease continuum, which is defined by preclinical Alzheimer’s, prodromal dementia, and Alzheimer’s disease.
A recent meta-analysis by Gustafsson and colleagues, published in the journal Alzheimer’s & Dementia, aims to shed some light on this issue by estimating the global prevalence of preclinical and prodromal Alzheimer’s disease. The study evaluated all literature published in the past 10 years and identified 55 articles that indicated estimates of the prevalence of AD at any stage of the disease, with or without confirmation of vital signs.
In the United States, the authors estimated that as many as 28.4 million individuals over the age of 50 have persistent Alzheimer’s disease, with 20 million and 5.6 million having preclinical and prodromal Alzheimer’s disease, respectively. Such an estimate is well above the roughly 2.3 million individuals over 60 who are expected to be diagnosed with Alzheimer’s disease, and about 2.3 million more people with mild cognitive impairment in the United States this year, according to GlobalData.
While the inclusion of the 50-59 age group in Gustafson’s estimates explains some of this difference, individuals’ estimates of Alzheimer’s persistence were lowest in this age group and thus did not significantly influence the discrepancy. Therefore, the inclusion of individuals with preclinical and prodromal Alzheimer’s disease in prevalence estimates suggests that millions of individuals in the United States are at risk of developing Alzheimer’s disease, many of whom do not know they are at risk because of the difficulty of diagnosing preclinical and prodromal Alzheimer’s disease.
While, in many cases, individuals in the continuing continuum will not develop Alzheimer’s disease, the large size of this group, combined with an aging population in the United States, has significant implications for Alzheimer’s treatment and prevention. This presents an opportunity to expand existing research and increase the focus of health care systems on populations in the early stages of the disease. This focus should aim to clarify factors that may influence the development of Alzheimer’s disease, such as socioeconomic, racial, and gender disparities, and aim to screen individuals earlier and more routinely. In doing so, prevention and mitigation strategies can be deployed more effectively and reduce the overall burden of Alzheimer’s disease.