Number of Alzheimer's 100 years ago
Executive summary
Estimates of how many people had “Alzheimer’s” around 100 years ago are not available as a single, reliable count because the disease was only newly described in the early 20th century and diagnostic systems, surveillance and recording were rudimentary; historical reviews note the term “Alzheimer’s disease” entered the literature in 1910 after Alois Alzheimer’s 1907 case report [1]. Modern global and U.S. prevalence figures — for comparison — put dementia at tens of millions worldwide and about 5.8 million Americans age 65+ in recent decades [2] [3] [4].
1. Why a precise headcount from a century ago is impossible
Medical historians and reviews explain that the label “Alzheimer’s disease” was introduced only in the 1910s and clinical recognition, biomarkers and diagnostic criteria evolved slowly thereafter, so systematic case-finding and population surveillance that underlie modern prevalence estimates did not exist around 1925; historical summaries emphasize the term has been in use for “over 100 years” only since 1910 [1]. Available sources do not provide a numerical prevalence or incidence estimate for Alzheimer’s disease circa 1925.
2. How modern numbers help frame the change
Contemporary authoritative sources report dementia and Alzheimer’s prevalence in the millions: global dementia counts have been cited in the tens of millions and Alzheimer’s is the single most common form, accounting for roughly 60–70% of dementia cases [5] [3]. U.S.-focused reports put Alzheimer’s patients among older adults in the millions — for example, some reviews and fact sheets cite about 5.8 million Americans age 65+ with Alzheimer’s in recent years [2] [4].
3. Reasons for the apparent rise in cases since the early 20th century
Three documented drivers explain why Alzheimer’s appears far more common now than a century ago: (a) population aging — far more people now reach the ages at greatest risk; (b) better recognition, diagnostic criteria and recording of cause of death and morbidity; and (c) formal epidemiologic surveillance and research that create the counts we use today [6] [7]. The Alzheimer’s Disease Facts and Figures reports highlight how modern surveillance tracks prevalence, incidence and mortality systematically [6] [7].
4. Diagnosis gaps then and now — and why that matters
Even today, many people with dementia go undiagnosed: international reports estimate that a large fraction of people living with dementia have not received a formal diagnosis, with recognition in primary care varying from roughly 20–50% in high-income countries and far lower in some low- and middle-income settings [8]. That chronic under-detection means historical counts — when diagnosis was rarer and stigmatized — would have missed most cases, making any retrospective headcount unreliable [8].
5. What historians and scientists actually document about early Alzheimer’s
Scientific histories note Alois Alzheimer’s first detailed neuropathologic description in 1907 and the subsequent gradual adoption of the eponym over the following decades; reviews recommend reading the early clinical and pathological literature to understand changing definitions [1]. The literature frames Alzheimer’s more as an evolving diagnostic concept than a fixed category with stable historical prevalence [1].
6. How to think about “number of Alzheimer’s 100 years ago” for practical use
If your aim is historical comparison, use contextual metrics — age-specific mortality, reported cases in clinical series, or archival hospital records — recognizing that none equates to modern population prevalence because surveillance, diagnostic criteria and social attitudes were different [1] [6]. If you need a working benchmark, compare modern, well-documented estimates (e.g., 5.8 million Americans 65+ in recent decades or global dementia in the tens of millions) to the qualitative historical record that shows far fewer recorded cases simply because the illness was less often recognized or recorded [2] [3].
Limitations and next steps: primary sources supplied here do not include any numeric prevalence estimate for Alzheimer’s disease circa 1925; to pursue a historical estimate you would need archival mortality data, contemporaneous hospital records or population studies from the 1920s and expert historical epidemiology analyses, none of which are cited in the available sources (not found in current reporting).