Digging Deeper: What Can We Really Learn about Dementia from History?

We appreciate the provocative article by Finch and Burstein [1]. The authors argue that the advanced dementias of old age might largely be conditions linked to environmental toxins and unhealthy lifestyles associated with modern societies. As evidence to support this idea, they point to recent research showing that the Amerindian group the Tsimané have rates of mild cognitive impairment (MCI) that are comparable to modern Western societies, but comparably very low rates of advanced dementia. They argue that the Tsimané’s isolation in the Amazon basin gives them a milieu of environmental exposures and lifestyle that is analogous to pre-industrial societies such as those in ancient Greece and Rome. They survey Greco-Roman medical, legal, and literary texts describing old age and find descriptions of conditions that might today be characterized as MCI but a paucity of descriptions of frank dementia. This is an intriguing argument with significant bearing on the Alzheimer’s disease field today.

In these comments, we want to make the case for a more genuinely historical approach to dementia than the authors have taken and expand on some of the broader public health implications that their article gestures at but does not explore.

As a discipline, history is grounded in a commitment to reconstructing and understanding the past on its own terms. The approach the authors take in this article is essentially the opposite of this, using ancient descriptions of dementia with no attempt to situate them in the broader social and cultural context in which they were created. Rather, they use historical evidence in an ahistorical, instrumental fashion to support their thesis that dementia is caused primarily by environmental toxins. While we appreciate their argument and do not mean to dismiss it, we would caution that this ahistorical approach entails a significant risk of error. As the well-known aphorism goes, “absence of evidence is not evidence of absence.” There are many reasons why an existing group of people or a particular human experience may be absent from textual sources from any historical period, and the authors do not seem to have considered that in this article. To reach a meaningful conclusion about whether and how dementia was experienced in ancient societies will require a much more rigorous historical study, grounded in an analysis of the broader social and cultural contexts of these textual sources.

More broadly, a genuinely historical approach would help open the dementia field up to different ways of thinking. History is a humbling discipline, reminding us that every perspective and every concept is limited at least to some extent by historical and cultural context. In the current article, such an approach might appropriately lead to questions about concepts that the authors deploy uncritically, such as MCI. While there has arguably been utility to the MCI concept in research context, its value in clinical settings is controversial due to concerns about variability, over-medicalization, and stigma. It should be acknowledged that the construct was created, just like earlier abandoned terms such as Aging Associated Memory Impairment, in a particular place and time to serve a particular set of interests. It may be distorting to apply it in some contexts, and especially to societies that may have significantly different ideas about cognitive ability and aging.

A more historically grounded approach might also lead the authors to a fuller consideration of the contemporary public health consequences of their argument. Indeed, in the past decade, an emerging literature has documented, somewhat surprisingly, the decreasing relative rates of dementia in the US and other Western European countries [2–4]. While total numbers of people affected by dementia have risen (due to growing populations), the relative risk of older persons developing dementia has consistently declined by 13% per decade since the 1980s in these Western countries (Alzheimer’s disease has declined by 16% per decade) [2].

Researchers have linked this phenomenon with population health-level factors such as improved vascular health, increased smoking cessation, increased total years of education, and the removal of lead from environments via the de-leading of gasoline achieved in the mid-20th century [5]. These actions are linked with state-driven policies—in a US context, the establishment of Medicare/Medicaid, the Federal Cigarette Labeling and Advertising Act of 1966 and the Public Health Cigarette Smoking Act of 1969, the GI Bill, Pell Grants, the Clean Air Act, etc.—that, by directly and indirectly influencing social determinants of brain health (i.e., prevention and treatment of cardiovascular disease, increased access to education, lower exposure to neurotoxins), appear to have helped move the needle on dementia risk and incidence for older adults now entering their graying years. These aging cohorts have generationally benefited from the salutary environments instantiated by 20th-century policies.

Such landmark findings would seem to strongly support the authors’ overall thesis that built environments have substantial impact on brain aging and are also an invitation to think more critically about the deleterious consequences of contemporary political-economic organization. Indeed, the positive brain health trends we have witnessed over the past decade may soon begin reversing due to the reorientation of Western societies over the last several decades around radical free-market principles. This shift, commonly referred to as “neoliberalism” or “hyper-capitalism”, began in the 1970s in response to the crisis of stagflation and international oil shocks. It has transitioned the government’s role from capital control, redistribution, and public investment, as was generally the commitment of Western states during the post-Depression and post-World War II period in the mid-20th century, to facilitating global capital mobility, market expansion and deregulation, decreased taxation of the wealthy, de-unionization, and cutting and privatizing public goods and services.

As Western states have gradually reduced their public commitments to citizens and pursued neoliberal policies aligned with a faith in the efficiency of markets, the societal conditions of the mid-20th century that fostered progress on dementia incidence have been altered, with many of the trends that precipitated gains in brain health reversed. For instance, vascular health in the US is declining at a staggering rate. Six in ten Americans currently live with a chronic disease, many related to vascular factors (e.g., diabetes, cardiovascular disease, stroke, obesity, hypertension, high cholesterol, etc.), and four in ten live with at least two conditions [6]. From an access to care standpoint, over 80 million US citizens remain un- or under-insured [7], largely failing to receive primary or secondary prevention for vascular risk factors that likewise affect late-life risk for dementia. As opposed to the state’s role in heavily subsidizing higher education in most Western countries in the 20th century, tuition costs within a hyper-marketized landscape have skyrocketed over the last several decades, causing a recent trend towards falling cumulative years of education, especially for men [8]. So too are we dealing with a renewed lead crisis, only this time with the heavy metal present in our public drinking water due to aging infrastructure, political inaction, and austerity-era policies that have gutted regulatory oversight [9, 10].

It is unfortunate the authors did not align their analysis with the emerging contemporary literature as it could have helped clarify and expand upon the environmental relationships they are trying to draw out. Generally, there has been less attention given to the counter-intuitive finding of reduced dementia incidence in Western countries, largely because the field has been so deeply invested in biomolecular approaches interceding in neurodegenerative processes. But in the contemporary world, just as in ancient Greece, Rome, and in the Amazon, the organization of society and our broad commitments to public health and social welfare (or lack thereof) appear to be the biggest driver of brain health.