Sigh-entific Nonsense
A once venerable magazine and a research article it dramatizes reflect the state of science and science journalism.
Dementia and Alzheimer’s are among the most devastating human diseases, most commonly impacting adults over age 65. Terminal cancers certainly inflict far more pain and suffering than any form of cognitive decline. While dementia or Alzheimer’s victims’ absence of pain and suffering is certainly some solace compared to cancer, watching a loved one lose their independence, ability to communicate, and ultimately their dignity over years extracts a different but still very heavy toll on family members and close friends.
According to the Alzheimer’s Association, approximately 7 million Americans age 65 and older are living with the disease today. Among that age cohort, Alzheimer’s is the fifth leading cause of death.
The causes of dementia, Alzheimer’s and cognitive decline remain unknown. Heredity is clearly a risk factor.
Many studies have identified a variety of other possible associations. The 2024 Lancet Commission on Dementia identifies 14 additional contributing risk factors.
Age is the most obvious. After age 65, the prevalence of dementia doubles roughly every five years. But age and genetics are non-modifiable risk factors. Neither are in your control.
Other risk factors associated with dementia and Alzheimer’s relate to lifestyle. These include diet, exercise, smoking, alcohol and drug use, physical inactivity and all of their associated consequences on cardiovascular health, and even education. All of these are modifiable. (We all make choices.)
Investigations attempting to discover causal connections between environmental exposures and dementia, Alzheimer’s and cognitive decline have increased over the last two decades. Exposure to pollutants like metals in air and drinking water are a key focus.
Some degree of association between dementia and Alzheimer’s and pollutant-related environmental exposures would seem logical on the surface. Certain heavy metals (e.g. lead and mercury), some pesticides (e.g. organophosphates) and chlorinated solvents, for example, have known neurotoxic effects in humans.
But the idea of a connection between exposure to “greenspace” and these cognitive diseases had never crossed our minds. Nor would it ever have.
Until we recently learned that a group of scientists had attempted to assess the relationship between environmental “greenness” (time spent in greenspace, parks, open space in urban areas) and dementia, Alzheimer’s, and cognitive impairment. We were tipped off to the research article by Dr. Heather Heying, who closed a recent episode of the Dark Horse podcast with her husband Dr. Bret Weinstein describing its coverage in a well-known science magazine.
The story appeared last month on March 31 in Scientific American. Had it been published a day later we would have suspected it was an April Fool’s Day joke. (It would have made for a more believable headline in The Onion or The Babylon Bee.)
What did the study find, and how much credence do we give it? How did Scientific American’s depiction of the study leave readers with the wrong impression while doing its own reputation no favors?
We begin the story (and end it) with Scientific American. Founded in 1845, it is the oldest mainstream science publication in continuous circulation in the United States. The list of scientific luminaries whose writing has appeared in the publication’s pages over the decades includes names like Albert Einstein, Marie Curie, Nikola Tesla, and Jonas Salk. Readers may remember the magazine as a non-political, objective, and reliable source of science news from their youth. (A quaint notion today.)
But as James B. Meigs wrote in a Spring 2024 City Journal piece with the not-so-flattering title Unscientific American:
“In the twenty-first century, however, American scientific media, including Scientific American, began to slip into lockstep with progressive beliefs.”
Meigs’ article incorporates Michael Shermer’s first-hand experiences as a regular columnist on the magazine’s payroll for nearly twenty years, providing examples of Scientific American’s metamorphosis from objective reporter of science to political advocacy across a wide variety of topics, ranging from race to gender to climate change to the Covid-19(84) pandemic. When the magazine’s editors endorsed a candidate for President in 2020 for the first time in the publication’s nearly 200-year history, its transformation to political advocacy first, science second was effectively complete.
Scientific American described the findings of the study at issue as follows (emphasis added:)
You might presume that more green space is better, and that living on a few wooded acres with nothing but trees for miles around will lead to the lowest possible chance of dementia. It turns out this is not so simple. A 2022 research study led by Federico Zagnoli of the University of Modena and Reggio Emilia revealed that more green space is not always better. The researchers found a U-shaped association between exposure to green space and dementia risk—low levels of green space were associated with a higher likelihood of developing dementia, and medium levels were linked to a lower risk. But the highest level of green space exposure didn’t reduce dementia risk relative to the medium level—and in some cases even increased it! In other words, too little green space has an adverse effect, but so might too much of it.
It is instructive to note that Zagnoli, Emilia, etal (Zagnoli) is nearly three years old. It was published as an article in the July 20, 2022 edition of Current Environmental Health Reports. Why Scientific American chose now to highlight a research article nearly three years after its release is anybody’s guess.
Zagnoli attempts to assess “the relation between environmental greenness and risk of dementia and cognitive impairment.” The authors conducted no original research on the relationship in conjunction with their research paper, but rather a meta-analysis of existing research in the relevant scientific literature (a study of studies, if you will).
Meta-analysis studies systematically combine and analyze data from multiple independent studies on the same topic in an attempt to draw more robust conclusions. They aim to provide a higher level of evidence by pooling results, increasing statistical power, and reducing bias or inconsistencies found in individual studies.
Meta-analysis has its strengths and weaknesses. They can increase precision by pooling large datasets. They can resolve disputes when studies conflict with each other. And they can detect patterns or effects too subtle for smaller studies.
On the other hand, meta-analyses are subject to the same “garbage in-garbage out” (aka GIGO) risk as the original research on which they rely. They can suffer from heterogeneity complications, in which differences in study methods, populations, or settings can complicate combining data, producing misleading results. They are prone to publication bias, overemphasizing published studies which are more likely to report significant results, while ignoring unpublished null findings. Depending on how they are structured, they can be mined for predetermined answers rather than unfolding from a neutral hypothesis (via cherry picking studies for inclusion, or by p-hacking, or designing a study based on a narrow or leading question). This is not to suggest that all meta-analyses are flawed or that the Zagnoli researchers engaged in any or all of these actions.
The Zagnoli authors identified 269 relevant articles in the scientific literature, discarding 232 articles after analyzing their titles and abstracts. From the remaining 37, 25 more were excluded for various reasons, leaving the researchers with a total of 12 articles which provided individual-level data and reported the association of greenness with dementia and/or cognitive impairment. We note this is a relatively small number of studies for a meta-analysis.
The remaining twelve studies Zagnoli analyzes employ the two most common indices researchers use to measure greenness - normalized difference vegetation index (NDVI) and land use and land cover (LU/LC). NDVI uses satellite imagery and has better ability to measure greenness at fine spatial resolutions, making it ideal for large-scale epidemiological studies. LU measures land use (a categorical indicator of what covers the land) and LC measures land cover in terms of the actual physical or biological surface. LU/LC can differentiate between types of green spaces and account for human interaction with ecosystems. The more context-specific data is useful for understanding how accessible or usable greenspaces might influence dementia outcomes, especially in urban settings, and is complementary to NVDI data.
The publication period of the twelve studies ranged from 2015 to 2022. Three were conducted in Europe (two in UK, one in the Netherlands), five in North America (two in Canada, three in US), three in Asia (one each in China, Taiwan, and Hong Kong), and one in Australia.
The specific research question was:
“In the adult population, what is the effect of greenness on risk of cognitive impairment or dementia from epidemiological studies?”
Comparing the highest versus lowest exposure categories of greenness assessed using the six NDVI studies or six LU/LC 6 studies, the Zagnoli researchers found “no association with dementia.” But a dose-response analysis of (only) three of the LU/LC studies “indicated a U-shaped association, but estimates were imprecise,” as shown in Zagnoli’s Figure 3 below (with our notes added). The vertical axis represents risk ratio (RR) for dementia (where 1.0 is the neutral value, >1 implies higher risk, <1 reduced risk), and the horizontal axis represents the level of exposure to “greenness” (where 0 is the minimum and 1 the maximum).
The dose-response curve between dementia and “greenness” in those three LU/LC-based studies indicated a lower risk for an “intermediate range of exposure” (our “Goldilocks” arrow added to Figure 3 above). However, as the authors note:
But at the highest levels of greenness, there was little evidence of protection, with the RR (risk ratio) approaching and slightly exceeding 1. Two of the three included studies demonstrated a U-shaped relation while the other suggested no association.
At the highest level of “greenness” the RR actually exceeds 1? That conclusion implies the highest levels of exposure to “greenness” actually increase risk of dementia, Alzheimer’s, and/or cognitive decline rather than attenuate it.
Count us highly skeptical that any direct causal relationship exists between the amount of time in, or exposure, to “greenness” - or nature more broadly - and dementia or cognitive decline. Frankly, the premise itself is absurd on its face.
The Zagnoli findings contradict a wealth of research concluding numerous benefits to mental health generally and brain health specifically from time spent in nature, from urban “greenspaces” to the most remote wilderness areas. These benefits are far more certain than the speculative risks of dementia or cognitive decline for higher exposure levels to “greenness” than the “goldilocks” window the Zagnoli findings suggest.
No concrete answer to the research question (“In the adult population, what is the effect of greenness on risk of cognitive impairment or dementia from epidemiological studies?”) could be derived from the Zagnoli analysis of the selected literature. Given that science cannot presently answer any questions about any causal relationships between environmental-related exposures and dementia, Alzheimer’s, or cognitive decline, that outcome is not surprising.
Heterogeneity problems between the 12 underlying studies add to our skepticism. How might “greenness” be defined differently across 12 studies in different societies (one controlled by a communist regime) on four different continents?
The time of exposure (to “greenness”) assessment varies across the 12 studies. Some use an average of the seasons, others use a single measure.
Errors in exposure classification are likely given how the 12 studies measured “greenness” spatially. Most measured in relation to a study participant’s address. Exposure in other settings (in particular recreation) was not taken into consideration. Those with serious, lifelong outdoor passions will recognize this as a significant shortcoming.
Importantly, none of the 12 underlying studies in the Zagnoli meta-analysis control for virtually any of the other risk factors associated with dementia, Alzheimer’s, or cognitive decline. Differences in study participants’ diet, exercise, lifestyle choices and especially environmental exposures like air pollution and water contamination are likely to be vast. For example, consider the differences in air quality (mercury, particulate matter, etc.) between Florida (location of one of the 12 studies Zagnoli used, where only 3% of electricity generated statewide is from coal), and China (another study location, but with ~60% electricity from coal). Such lack of controls makes drawing conclusions from a U-shaped association derived from only three underlying studies speculative.
We give the Zagnoli authors credit for identifying the numerous and non-trivial limitations, heterogeneity complications, and other confounding factors that affected their analysis and, by implication, limit its reliability. The Discussions and Conclusions sections of their research article explicitly acknowledge these issues.
We can give no such quarter to Scientific American for the lack of such balance in its presentation of the study’s findings. That absence is evident from the very first paragraph in its article (emphasis ours):
But new research suggests that when it comes to the risk of dementia and Alzheimer’s disease, easy access to nature can sometimes help but, at other times, can be too much of a good thing.
Whereas the Zagnoli authors are reasonably careful to qualify the limitations of their conclusions, Scientific American throws caution to the wind, leaving readers to worry that spending more time closer to nature could increase their risk of dementia (emphasis added):
So, the conclusion is that green space itself is not bad for your brain health, but living on a few acres of land surrounded by forest and farmland might increase your risk of dementia in other ways. Although trees have a positive effect, they are no substitute for a nearby hospital, local community center and a walkable neighborhood with friendly neighbors. Aiming for the lowest possible dementia risk is all about a balance: enough neighborhood density to have easy access to services and social support but plenty of trees for a walk in the park.
No one would consider trees as a substitute for a nearby hospital, local community center or relationships with people. The suggestion and the sentence are sophomoric, yet perfectly illustrative of the state of science journalism in advanced nations today.
We would put the matter to Scientific American and its editors in a different way: although a nearby hospital, local community center and a walkable neighborhood may have a positive effect, they are no substitute for trees, mountains, rivers, marshes, wilderness areas, parks (whether your neighborhood park or an expansive National Park or Forest), wildlife, fish, and time immersing oneself in such “greenness”.
We close by noting that the members of the environMENTAL team, long passionate about the outdoors, will take our chances spending the most time we can in “greenness” with zero worry about increasing our risk of dementia or Alzheimer’s. On the contrary, we will do so with express intent: to avoid the day where we might regret failing to engage in those outdoor passions with every opportunity we had, in the event we someday suffer any form of cognitive decline and no longer can.
We highly encourage readers to do the same. Do not worry about your brain or mental health while doing so.
Too much exposure to “greenness” or nature does not increase the risk of dementia, Alzheimer’s, or cognitive decline. At a time when too many people in wealthy, advanced nations are too sedentary, glued to their iPhone screens, addicted to social media, with poor diets, increasingly disconnected to the natural world around them, and the sources of their food and energy and the ecosystem services on which they rely, Scientific American causing readers to question their time outdoors looks more like sigh-ence than science.
You will not lose your mind no matter how much time you spend exposed to “greenness”. But it’s not obvious to us the same can be said about long-term exposure to legacy media reporting on science, particularly sigh-entific nonsense.
“Like” this post if you can differentiate between science and sigh-ence, and the latter makes you sigh.
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Substack came along just in time…….
Scientific American= woke mindvirus. Sad.