The role of air pollution in cognitive impairment and decline

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trader32176
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The role of air pollution in cognitive impairment and decline

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The role of air pollution in cognitive impairment and decline

June 2020

https://www.sciencedirect.com/science/a ... 8620300991

Highlights



The area of air pollution on cognitive decline has become an active area of epidemiological research.


Results from epidemiological studies indicate that exposure to air pollution can have adverse effects on cognitive decline and impairment.


Abstract


The biological pathways and the extent to which air pollution can affect the cognitive decline in the elderly is not fully understood. In recent years, the impact of air pollution on cognitive impairment has become an active area of epidemiological research and several studies provided supporting evidence. This short review focuses on epidemiological studies in older adults investigating the associations between long-term air pollution exposure and cognitive impairment and decline. Most studies were observational studies and reported assessment of cognitive function using different cognitive scores and air pollution exposure in adults older than 50 years. The results from these studies indicate that exposure to ambient air pollution can have adverse effects on cognitive decline and impairment, but the overall results are heterogeneous and not fully conclusive. The number of epidemiological studies are still limited and additional longer-term studies are needed to confirm the findings. Understanding the relationship between air pollution and cognitive impairment is important to develop preventive measures and to address the needs of people living with cognitive impairment.

1. Background

Air pollution has been associated with various adverse health outcomes including respiratory and cardiovascular diseases (Rajagopalan et al., 2018; Brunekreef and Holgate, 2002). In recent years there has been an emerging body of evidence of epidemiological studies linking air pollution exposure to neurological disorders (Weisskopf et al., 2015); stroke (Sun et al., 2019) and cognitive functions in children and the elderly (Power et al., 2011; Calderon-Garciduenas et al., 2011; Block et al., 2012). Studies on air pollution exposure with cardiovascular and cerebrovascular diseases suggest a harmful impact on the brain and cognitive processes through vascular and inflammatory mechanisms (Thal et al., 2012). However, the extent to which air pollution can affect cognitive decline and dementia in the elderly is not fully understood.

Ambient air pollution exposures are ubiquitous and affecting large populations worldwide. Over 90% of the worlds’ population is exposed to detrimental levels of air pollution exceeding the World Health Organisations Air Quality Guidelines (World Health Organisation, 2019a), making air pollution one of the leading risk factors worldwide for morbidity and mortality. Exposure to high levels of ambient air pollution can affect people at all stages of life, particularly vulnerable subgroups such as children and the elderly. Both, short and long-term effects have been linked to adverse health outcomes and premature mortality (Lelieveld et al., 2015) with the long-term exposures being the greater risk. However, even low levels of air pollution have been associated with cardiovascular health outcomes (Miller et al., 2007).

With the growing of the elderly population (population aged 65 or older), accounting for 8.5% (617 million) of the world's population in 2015 and expected to double to over 16.7% (1600 million) in 2050 (He et al., 2015), it's important to understand the needs of the aging population. As increasing age is the strongest known risk factor for cognitive impairment and dementia and due to the globally aging population, the number of people living with these neurological disorders is expected to rapidly grow in the coming years. According to a report from World Health Organization (WHO), worldwide, dementia affected around 50 million people (or roughly 5% of the world's population those above the age of 60 years) in 2015, with approximately 60% living in low- and middle-income countries (LMIC). Every year, there are nearly 10 million new cases and the total number of people with dementia is projected to reach 152 million in 2050 (World Health Organization, 2019b). In the last 15 years, the impact of air pollution on cognitive impairment in the elderly has become an active area of epidemiological research and several studies provided supporting evidence.

2. Ambient air pollution


There are various sources of air pollution and depending on their characteristics, they differ in composition and conditions under which they are produced. Common sources of air pollution are the combustion of fossil fuels from traffic as well as industrial, residential and agricultural sources. Pollutants of concern are particulate matter (PM), and gases such as sulfur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO). They are the so-called ‘primary’ pollutants, which are released directly into the atmosphere. Secondary pollutants are formed in the atmosphere, largely from the primary pollutants under UV exposure. One of such secondary pollutants is ozone (O3), which is formed from nitrogen oxides and hydrocarbons in the atmosphere under UV exposure.

Ambient particulate matter (PM) is one of the components of ambient air pollution, which is produced either by natural processes such as volcanic activity or dust storms, or by human activity. PM is usually classified by its size or aerodynamic diameter; PM10 are particles<10 μm (μm) in aerodynamic diameter; PM2.5 particles are <2.5 μm in diameter; and PM0.1 particle are<0.1 μm (or 100 nm) in diameter. All PM2.5 and PM0.1 are included in PM10, therefore, adverse effects attributed to PM10 could be caused by smaller particles. Ultrafine particles (PM0.1) especially can be inhaled deeply into the lungs and can infiltrate the blood stream, therefore they may be more harmful to human health than the larger particles. The term “coarse particles” is used to refer to particulates between PM10 and PM2.5 in size. PM pollution is not a specific single component of air pollution, but is a complex mixture of extremely small particles and droplets. It consists of a number of components including acids, organic chemicals, metals, and soil or dust particles (Donaldson and MacNee, 2001). The major source of air pollution nowadays is from traffic-related sources and from the industry. Exposure to traffic-related air pollutants (TRAP) have been associated with cognitive decline and dementia in the elderly (Block and Calderon-Garciduenas, 2009).

3. Cognitive impairment

Cognitive decline is a major concern in the elderly population. The risk of developing cognitive decline after the age of 65 is estimated to be 30–40%. The incidence of developing cognitive decline is increasing with increasing age (Alzheimer’s Association and Centers for Disease Control and Prevention, 2013) and cognitive impairment ranges from mild to severe. Changes in the brain may occur 15–20 years before obvious symptoms affecting memory, thinking or behaviour can be clinically detectable. The “preclinical stage” may be detected by biomarker abnormalities (excess amyloid plaque accumulation in the brain, presence of tau protein in cerebrospinal fluid, grey matter loss in the brain, etc.) in the brain but not yet meet accepted clinical criteria for mild cognitive impairment (MCI). In the “prodromal stage” (i.e., MCI), people may begin to notice changes in cognitive functions and also have a positive biomarker test, but still be able to do their everyday activities. The prodromal stage follows dementia in which both cognition and daily function are deteriorated (Parnetti et al., 2019).

In addition to age, there are several other risk factors that contribute to cognitive decline, including genetic risk factors and physical health status such as cardiovascular disease (Breteler et al., 1994). Certain medical conditions are associated with an increased risk of developing dementia, including hypertension, diabetes, hypercholesterolemia, obesity, and depression (World Health Organization, 2019b). Other possible risk factors contributing to cognitive decline are early-life education, physical activity, and smoking (Barnes et al., 2013; Baumgart et al., 2015). Many of these risk factors are also influenced by ambient air pollution or are associated with it such as cardiovascular diseases. Although cognitive decline precedes dementia, decline in cognition does not always indicate subclinical dementia (Power et al., 2016). However, it is important to acknowledge that not all people with cognitive decline also progress to dementia and Alzheimer's disease.

4. Possible biological pathways

There are different hypotheses about how air pollutants can affect cognitive decline. One is that Tau and beta-amyloid (Aβ) deposits in the brain, however little to no research is available on how pollutants can affect the development of tau and Aβ protein in the brain. Current research suggests that cardiovascular and respiratory risk factors and conditions are possible mediators of the association between air pollution and cognitive decline (Hüls et al., 2018; Saito and Ihara, 2016; Toledo et al., 2013). Particulate matter has been associated with heart rate variability as well as other cardiovascular conditions (Adhikari et al., 2016). Global cortical Aβ deposition has also been linked to different cardiovascular diseases risk factors such as diabetes and hypertension (Gottesman et al., 2017). Further, ambient air pollution exposure has been linked to stroke and cerebrovascular diseases (Bejot et al., 2018). Air pollutants such as particles, nitrogen oxides, and ozone are potent oxidants and they may reach the brain and affect the central nervous system by oxidative stress and neuro-inflammation (Block and Calderon-Garciduenas, 2009; Fonken et al., 2011; Genc et al., 2012). Oxidative stress and neuro-inflammation are reported among the hypothesized biological pathways of neurological disorders (Berr et al., 2000; Cervellati et al., 2014; Droge and Schipper, 2007).

Particles may translocate directly to the brain via the nose to the olfactory bulb. The olfactory bulb has been found to be loaded with particulate matter and impaired olfactory function is a precursor of Alzheimer's disease (Calderon-Garciduenas et al., 1995; Fagundes et al., 2015). Furthermore, inhalation of air pollution and diesel exhaust has been shown to elicit inflammatory changes in the brain (Levesque et al., 2011; Calderon-Garciduenas et al., 2012).

5. Epidemiological studies on air pollution and cognitive decline


In recent years, the area of air pollution on cognitive decline has gained more interest and has become an active area of epidemiological research. Several studies on cognitive decline and different air pollutants were published. Most studies were observational studies and reported assessment of cognitive function using different cognitive scores and air pollution exposure in adults older than 50 years. Most studies were conducted in the US and Mexico, two are from Europe and one study from China. The results from all these studies are mixed. The study by Gatto et al. (2014) investigated 1500 older adults from the US using ozone (O3), PM2.5 and NO2. Participants with high exposure to these pollutants showed slight but not significant associations with general cognition scores. However, the individual cognitive scores for verbal learning were associated with PM2.5 exposures and ambient exposure to NO2 >20 ppb tended to be associated with lower logical memory. In addition, compared to the lowest level of exposure to ambient O3, exposure above 49 ppb was associated with lower executive function. All other scores did not show any association. The study by Ailshire and Clarke (2015) from the US also found association between PM2.5 and tests of the working memory and orientation. Older adults living in areas with high concentrations of PM2.5 had a test error rate 1.5 times greater than those exposed to lower concentrations, net of individual and neighborhood-level demographic and socioeconomic characteristics. Another study from Germany investigated elderly women from the Ruhr area and the association between NO2, PM10, and PM2.5 with scores of the CERAD test battery (Consortium to Establish a Registry for Alzheimer's Disease - Neuropsychological Assessment Battery) (Schikowski et al., 2015). They found an association between NO2 and one subtest of the CERAD test battery. In the same study population, they found that living close a major road (a distance of the participant's home address of at most 50 m to the next busy road with more than 10,000 cars per day) was also associated with a reduction in olfactory function and executive functions (Ranft et al., 2009). The MOBILIZE Boston Study observed that residential proximity to nearest major roadways (defined as roads having US Census Feature Class Code A1 (primary highway with limited access) or A2 (primary road without limited access)) was associated with poorer performance on cognitive tests of verbal learning and memory, psychomotor speed, language, and executive functioning. Generally, participants residing <100 m from a major roadway performed worst and performance improved monotonically with increasing distance. In addition, long-term average residential black carbon levels, a marker of traffic-related air pollution, were associated with a reduction in the Mini Mental State Exam (MMSE) (Wellenius et al., 2012). In the prospective Normative Aging Study (NAS) from the US, they could show that exposure to black carbon (BC) was also associated with the odds of having a “low” (≤25) MMSE score in older men (Power et al., 2011). The NHANES III study from the US (Chen and Schwartz, 2009) investigated the influence of exposure to PM10 and ozone with cognitive performance. They could show that higher exposure to PM10 or O3 was associated with poorer performance in all cognitive tests. Each 10-ppb increase in annual ozone was associated with increased cognitive scores equivalent to 3.5 and 5.3 years of aging-related decline in cognitive performance. A study in older adults from Mexico City found an association between the MMSE and living in urban areas compared to adults living in rural areas (Sanchez-Rodriguez et al., 2006). The Chinese Longitudinal Health and Longevity Survey (CLHLS) (Sun and Gu, 2008; Zeng et al., 2010) also assessed cognitive decline with MMSE and exposure to ambient air pollution was assessed by combining multiple air pollutants using Air pollution index (API). A 1-point increase in API was associated with worse cognitive performance in the MMSE.

There are only two investigated the incidence of air pollution exposure and cognitive decline. In the long-term Nurses’ Health Study from the US, Weuve et al. (2012), PM2.5 exposure showed a greater decline in global cognitive function compared to older women with less exposure. Their results indicated that the effect of a 10-μg/m3 increment in long-term PM exposure is cognitively equivalent to aging by approximately 2 years. In another prospective study from the UK, Tonne et al. (2014) could show that five-year averages of PM2.5 and PM10 increased changes in memory scores and reasoning in older men, but not verbal fluency. Additionally, the study of Tonne et al. mentioned that their results did not support the hypothesis that traffic-related particles are more strongly associated with cognitive function than particles from all sources.

6. Conclusion

The results from the above epidemiological studies indicate that exposure to ambient air pollution can have adverse effects on cognitive decline and impairment, but the overall results are heterogeneous and not fully conclusive. The number of epidemiological studies is still limited and additional longer-term studies are needed to confirm the findings. The majority of current studies are observational studies and only two studies investigated long-term associations. Direct comparison of the studies is difficult as they vary in design, used different tools to assess cognitive decline/impairment, measured air pollution exposure in various ways and were performed in different populations. However, with the burden of air pollution exposure increasing worldwide, the burden of cognitive decline will likely also grow. Understanding the relationship between air pollution and cognitive impairment is important to develop preventive measures and to address the needs of people living with cognitive impairment. If the evidence supporting such a causal relationship is further proved, regulatory actions for reducing the exposures would support gaining substantial health benefits.
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Re: The role of air pollution in cognitive impairment and decline

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Study: Air Pollution Increases Plaque Buildup in Brains of Seniors

11/30/20

https://www.kboi.com/news/study-air-pol ... f-seniors/


Older adults exposed to air pollution might have a heightened risk of abnormal “plaque” accumulation in the brain, a new study suggests.

Plaques refer to clumps of protein called beta-amyloid that build up in the brains of people with Alzheimer’s disease. In the new study, researchers found that among older adults with memory and thinking problems, those exposed to higher levels of air pollution were more likely to show plaque buildup on brain scans.

The findings do not prove air pollution causes plaques or dementia, said lead researcher Leonardo Iaccarino, a postdoctoral fellow at the University of California, San Francisco’s Memory and Aging Center.

But the results add to a body of research suggesting that air pollution is a risk factor for dementia.

A recent study, for example, found that older Americans living in polluted ZIP codes had higher odds of being hospitalized for dementia or Parkinson’s disease than people breathing cleaner air.

The new study is different in that it looked at air quality and its relationship to a “biomarker” in the brain, Iaccarino said.

The 18,000 study participants all had either dementia or mild cognitive impairment (problems with memory and thinking that can progress to dementia). Each underwent a PET scan to look for beta-amyloid deposits in the brain.

Iaccarino’s team used data from the U.S. Environmental Protection Agency to estimate people’s exposure to air pollution — both around the time of the PET scan and 14 years earlier, based on their ZIP codes.

Overall, 61% showed beta-amyloid clumps on their brain scans. And the odds inched up along with air pollution exposure.

People who lived in the most-polluted areas 14 years prior were 10% more likely to have evidence of plaques than those in the least-polluted areas.

Why? One question was whether heart disease or stroke could explain the connection. Air pollution can worsen those conditions, and they are linked to dementia risk.

But Iaccarino’s team accounted for heart disease and stroke diagnoses, as well as respiratory and neurological conditions, smoking habits, household income and other factors. And air pollution exposure, itself, was still a predictor for having beta-amyloid plaques.

Alzheimer’s researchers suspect that plaques begin to form in the brain years before dementia symptoms are apparent, Iaccarino said. So the current findings link air pollution to a brain pathology underlying the disease.

That, again, does not prove cause and effect. But based on lab research, Iaccarino said, it’s possible that air pollution directly affects brain health by causing inflammation.

Xiao Wu, a researcher at Harvard University in Boston, worked on the recent study linking air pollution to hospitalizations for dementia.

He called the new findings “important,” because they tie air pollution to the biology underlying Alzheimer’s.

Wu agreed that it’s plausible that air pollutants have a direct effect: Research suggests the microscopic inhaled particles can cross the blood-brain barrier, he noted, and possibly lead to sustained inflammation.

At this point, Wu said, research into air pollution and brain health is in early days, and much more is left to learn.

“It’s very important that we look at the modifiable factors that are related to dementia and other neurological conditions,” he said.

If air pollution does contribute to Alzheimer’s risk, Iaccarino said, it would be just one of many factors.

“Alzheimer’s is a very complex condition,” he said. “Air pollution may be a small, but significant, determinant.”

It’s significant, in part, because air quality can be improved.

In fact, Iaccarino noted, the Lancet Commission on Dementia recently added air pollution to its list of modifiable risk factors for the disease. Others include smoking, high blood pressure, physical inactivity and traumatic brain injury.

Iaccarino also stressed that the study did not look at single air-polluting events, like wildfires, but at average, daily-life exposures to dirty air.

It all suggests that even air pollution levels within “normal” range are associated with beta-amyloid in the brain, he said.

On the positive side, Iaccarino said, Americans are living with less-polluted air, on the whole, than in years past.

“Air quality in the U.S. has improved a lot in the last 20 years,” he said. “It’s going in the right direction.”

The findings were published online Nov. 30 in JAMA Neurology.
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Re: The role of air pollution in cognitive impairment and decline

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Study: Air pollution exposure may be linked to Alzheimer's disease risk

12/2/20


https://www.upi.com/Health_News/2020/12 ... 606861785/


Older adults exposed to air pollution might have a heightened risk of abnormal "plaque" accumulation in the brain, a new study suggests.

Plaques refer to clumps of protein called beta-amyloid that build up in the brains of people with Alzheimer's disease.

In the new study, researchers found that among older adults with memory and thinking problems, those exposed to higher levels of air pollution were more likely to show plaque buildup on brain scans.

The findings do not prove air pollution causes plaques or dementia, said lead researcher Leonardo Iaccarino, a postdoctoral fellow at the University of California, San Francisco's Memory and Aging Center.

But the results add to a body of research suggesting that air pollution is a risk factor for dementia.

A recent study, for example, found that older Americans living in polluted ZIP codes had higher odds of being hospitalized for dementia or Parkinson's disease than people breathing cleaner air.

The new study is different in that it looked at air quality and its relationship to a "biomarker" in the brain, Iaccarino said.

The 18,000 study participants all had either dementia or mild cognitive impairment -- problems with memory and thinking that can progress to dementia. Each underwent a PET scan to look for beta-amyloid deposits in the brain.

Iaccarino's team used data from the U.S. Environmental Protection Agency to estimate people's exposure to air pollution -- both around the time of the PET scan and 14 years earlier, based on their ZIP codes.

Overall, 61% showed beta-amyloid clumps on their brain scans. And the odds inched up along with air pollution exposure.

People who lived in the most-polluted areas 14 years prior were 10% more likely to have evidence of plaques than those in the least-polluted areas.

Why? One question was whether heart disease or stroke could explain the connection. Air pollution can worsen those conditions, and they are linked to dementia risk.

But Iaccarino's team accounted for heart disease and stroke diagnoses, as well as respiratory and neurological conditions, smoking habits, household income and other factors. And air pollution exposure, itself, was still a predictor for having beta-amyloid plaques.

Alzheimer's researchers suspect that plaques begin to form in the brain years before dementia symptoms are apparent, Iaccarino said. So the current findings link air pollution to a brain pathology underlying the disease.

That, again, does not prove cause and effect. But based on lab research, Iaccarino said, it's possible that air pollution directly affects brain health by causing inflammation.

Xiao Wu, a researcher at Harvard University in Boston, worked on the recent study linking air pollution to hospitalizations for dementia.

He called the new findings "important," because they tie air pollution to the biology underlying Alzheimer's.

Wu agreed that it's plausible that air pollutants have a direct effect: Research suggests the microscopic inhaled particles can cross the blood-brain barrier, he noted, and possibly lead to sustained inflammation.

At this point, Wu said, research into air pollution and brain health is in early days, and much more is left to learn.

"It's very important that we look at the modifiable factors that are related to dementia and other neurological conditions," he said.

If air pollution does contribute to Alzheimer's risk, Iaccarino said, it would be just one of many factors.

"Alzheimer's is a very complex condition," he said. "Air pollution may be a small, but significant, determinant."

It's significant, in part, because air quality can be improved.

In fact, Iaccarino noted, the Lancet Commission on Dementia recently added air pollution to its list of modifiable risk factors for the disease. Others include smoking, high blood pressure, physical inactivity and traumatic brain injury.

Iaccarino also stressed that the study did not look at single air-polluting events, like wildfires, but at average, daily-life exposures to dirty air.

It all suggests that even air pollution levels within "normal" range are associated with beta-amyloid in the brain, he said.

On the positive side, Iaccarino said, Americans are living with less-polluted air, on the whole, than in years past.

"Air quality in the U.S. has improved a lot in the last 20 years," he said. "It's going in the right direction."

The findings were published online this week in JAMA Neurology.
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Re: The role of air pollution in cognitive impairment and decline

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Air Pollution Reduces IQ, a Lot

November 18, 2019


https://marginalrevolution.com/marginal ... a-lot.html

(Background info on earlier studies starts here)

The number and quality of studies showing that air pollution has very substantial effects on health continues to increase. Patrick Collison reviews some of the most recent studies on air pollution and cognition. I’m going to post the whole thing so everything that follows is Patrick’s.


Air pollution is a very big deal. Its adverse effects on numerous health outcomes and general mortality are widely documented. However, our understanding of its cognitive costs is more recent and those costs are almost certainly still significantly under-emphasized. For example, cognitive effects are not mentioned in most EPA materials.

World Bank data indicate that 3.7 billion people, about half the world’s population, are exposed to more than 50 µg/m³ of PM2.5 on an annual basis, 5x the unit of measure for most of the findings below.

Substantial declines in short-term cognitive performance
after short-term exposure to moderate (median 27.0 µg/m³) PM2.5 pollution: “The results from the MMSE test showed a statistically robust decline in cognitive function after exposure to both the candle burning and outdoor commuting compared to ambient indoor conditions. The similarity in the results between the two experiments suggests that PM exposure is the cause of the short-term cognitive decline observed in both.” […] “The mean average [test scores] for pre and post exposure to the candle burning were 48 ± 16 and 40 ± 17, respectively.” – Shehab & Pope 2019.
Chess players make more mistakes on polluted days: “We find that an increase of 10 µg/m³ raises the probability of making an error by 1.5 percentage points, and increases the magnitude of the errors by 9.4%. The impact of pollution is exacerbated by time pressure. When players approach the time control of games, an increase of 10 µg/m³, corresponding to about one standard deviation, increases the probability of making a meaningful error by 3.2 percentage points, and errors being 17.3% larger.” – Künn et al 2019.
A 3.26x (albeit with very wide CI) increase in Alzheimer’s incidence for each 10 µg/m³ increase in long-term PM2.5 exposure? “Short- and long-term PM2.5 exposure was associated with increased risks of stroke (short-term odds ratio 1.01 [per µg/m³ increase in PM2.5 concentrations], 95% CI 1.01-1.02; long-term 1.14, 95% CI 1.08-1.21) and mortality (short-term 1.02, 95% CI 1.01-1.04; long-term 1.15, 95% CI 1.07-1.24) of stroke. Long-term PM2.5 exposure was associated with increased risks of dementia (1.16, 95% CI 1.07-1.26), Alzheimer’s disease (3.26, 95% 0.84-12.74), ASD (1.68, 95% CI 1.20-2.34), and Parkinson’s disease (1.34, 95% CI 1.04-1.73).” – Fu et al 2019. Similar effects are seen in Bishop et al 2018: “We find that a 1 µg/m³ increase in decadal PM2.5 increases the probability of a dementia diagnosis by 1.68 percentage points.”
A study of 20,000 elderly women concluded that “the effect of a 10 µg/m³ increment in long-term [PM2.5 and PM10] exposure is cognitively equivalent to aging by approximately 2 years”. – Weuve et al 2013.
“Utilizing variations in transitory and cumulative air pollution exposures for the same individuals over time in China, we provide evidence that polluted air may impede cognitive ability as people become older, especially for less educated men. Cutting annual mean concentration of particulate matter smaller than 10 µm (PM10) in China to the Environmental Protection Agency’s standard (50 µg/m³) would move people from the median to the 63rd percentile (verbal test scores) and the 58th percentile (math test scores), respectively.” – Zhang et al 2018.
“Exposure to CO2 and VOCs at levels found in conventional office buildings was associated with lower cognitive scores than those associated with levels of these compounds found in a Green building.” – Allen et al 2016. The effect seems to kick in at around 1,000 ppm of CO2.

Alex again. Here’s one more. Heissel et al. (2019):

“We compare within-student achievement for students transitioning between schools near highways, where one school has had greater levels of pollution because it is downwind of a highway. Students who move from an elementary/middle school that feeds into a “downwind” middle/high school in the same zip code experience decreases in test scores, more behavioral incidents, and more absences, relative to when they transition to an upwind school”

Relatively poor countries with extensive air pollution–such as India–are not simply choosing to trade higher GDP for worse health; air pollution is so bad that countries with even moderate air pollution are getting lower GDP and worse heath.
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Environmental Toxicity and Poor Cognitive Outcomes in Children and Adults

2014 Jan-Feb



https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4247328/

Abstract

Extensive literature has already documented the deleterious effects of heavy metal toxins on the human brain and nervous system. These toxins, however, represent only a fraction of the environmental hazards that may pose harm to cognitive ability in humans. Lead and mercury exposure, air pollution, and organic compounds all have the potential to damage brain functioning yet remain understudied.
In order to provide comprehensive and effective public health and health care initiatives for prevention and treatment, we must first fully understand the potential risks, mechanisms of action, and outcomes surrounding exposure to these elements in the context of neurocognitive ability. This article provides a review of the negative effects on cognitive ability of these lesser-studied environmental toxins, with an emphasis on delineating effects observed in child versus adult populations. Possible differential effects across sociodemographic populations (e.g., urban versus rural residents; ethnic minorities) are discussed as important contributors to risk assessment and the development of prevention measures. The public health and clinical implications are significant and offer ample opportunities for clinicians and researchers to help combat this growing problem.

Introduction

The effect of environmental toxins on the brain and nervous system has been studied and documented extensively. A majority of the existing research has focused on the detrimental effects of heavy metals, however, while it appears that exposure to heavy metals represents only a portion of the total environmental health risks. For example, the damaging effects of air pollution on the brain, and particularly on intelligence, are being increasingly viewed as a significant concern. Another important concern is exposure to organic chemical compounds (such as polychlorinated biphenyls and dioxins) with toxic effects. What is particularly troubling about these compounds is that they can accumulate in animals and therefore can be delivered to humans via food products (Tuomisto, Vartianen, & Tuomisto, 2011).

Pollution is a complex issue affecting under-developed as well as developed countries. Socioeconomic issues are also relevant; people living in urban or impoverished areas may face greater exposure. Combatting pollution is a unique challenge, as it can require significant participation and economic support across all levels of government, from local municipalities all the way up to national authorities. All of these factors make pollution a broad research subject. As a result, this article will focus on some of the more recent developments and concerns regarding a few noteworthy pollutants. First, some of the major findings of the effects of the heavy metals lead and mercury on cognitive function will be reviewed. Although lead and mercury have been studied previously and extensively as mentioned earlier, they were included in this article due to recent developments regarding exposure. For example, the acceptable blood lead levels (BLLs) in children have decreased steadily over time. Mercury has reemerged as a threat due to its persistence in the food supply, particularly seafood.

Second, this article will also explore the potential effects of air pollutants and organic chemical pollutants on cognition. Special attention is given to the effects of pollution on specific population groups as well as more universal effects throughout each section of the article. The discussion on air pollution was included in this article because it is being increasingly viewed as a potential problem and its mechanisms of action are still not completely understood.

Air Pollution


Children


One major focus of research on the effects of air pollution is its potential impact on children. Due to the fact that children are continuously undergoing neurological and physical changes, they may be more susceptible to the harmful effects of toxins (Pinkerton & Joad, 2000). This is in contrast to adults, whose nervous systems are more mature and developed, and therefore more resistant to injury. Much of the research on children is centered on the effects of nitrogen dioxide (NO2) and its influence on the respiratory system (U.S. Environmental Protection Agency [U.S. EPA], 2010). NO2 principally acts as an irritant on the mucosa of the eye, nose, and throat as well as the rest of the respiratory tract and can decrease lung function in those with pulmonary disease (U.S. EPA, 2010).

Researchers are become increasingly worried, however, about the neurological effects of NO2. In a study of schoolchildren in China, researchers found a significant association between air pollution, particularly levels of NO2, and poorer results on neurobehavioral tests designed to measure the children’s sensory, motor, and psychomotor functions (Wang et al., 2009). A separate study examined the effects of indoor NO2 exposure from gas appliances in children and found a dose-response effect between NO2 levels and cognitive outcomes such as overall cognitive function, verbal abilities, and executive functioning (Morales et al., 2009). Children with greater exposure to NO2 also had an increased risk of developing attention-deficit hyperactivity disorder (Morales et al., 2009).

Other studies have not focused solely on the harmful effects of nitrogen dioxide but on air pollution’s effects as a whole. Using black carbon as a marker for air pollution in an urban birth cohort study, Suglia and coauthors (2008) found that increased amounts of black carbon were predictive of decreased cognitive function based on assessments with the Kaufman Brief Intelligence Test as well as on the Wide Range Assessment of Memory and Learning. In addition, a separate study of air pollution comparing children living in Mexico City to those living in less polluted areas of Mexico found significant deficits in the areas of fluid cognition, memory, and executive functions among the Mexico City children (Calderón-Garcidueñas et al., 2008).

Adults

Air pollution may be equally detrimental to the developed and mature nervous systems in adults. In a study using national data on pollution levels and neurobehavioral test results from the Third National Health and Nutrition Examination Survey, Chen and Schwartz (2009) found a significant association between ozone levels and decreased test results after adjusting for sociodemographic factors. These findings are limited, however, by the authors’ use of older data, indicating the need for further examination in a longitudinal study (Chen & Schwartz, 2009). The elderly may be particularly at risk for the potential health effects of air pollution. In a study conducted on elderly residents of urban China, increases in air pollution were associated with difficulties in cognitive functioning as well as performing activities of daily living (Sun & Gu, 2008). Among elderly women in Germany, an association as well as a dose-response relationship was found between long-term exposure to traffic-related air pollution and mild cognitive impairment (Ranft, Schikowski, Sugiri, Krutmann, & Kramer, 2009). Increased levels of ambient traffic-related air pollution (as marked by black carbon) was also associated with decreased cognitive function in a separate study of older men in the U.S. (Power, Weisskopf, Coull, Spiro, & Schwartz, 2011). Some researchers have expressed concern that these declines in cognition due to air pollution could be precursors to neurodegenerative diseases such as dementia and AD (Block & Calderón-Garcidueñas, 2009).

Potential Mechanisms of Action

Regarding the causal mechanism between air pollution and its potential negative health effects, human studies have suggested the brain as a potential target for injury, but the cross-sectional design often utilized in these studies makes it difficult to determine whether exposure to polluted air occurs before or after the negative cognitive effects are present. One of the first studies focused on findings in feral dogs exposed to polluted urban environments (Block & Calderón-Garcidueñas, 2009), and found damage to parts of the brain linked to the nasal pathway, such as the olfactory bulb, implicating the nasal pathway as a potential entry way for pollutants (Calderón-Garcidueñas et al., 2010). In the future, imaging studies in the brain and nervous system may provide clues as to which areas are most vulnerable. A study in mice exposed to air pollution identified the dorsal vagal complex as a potential target (Villarreal-Calderon et al., 2010). In addition, examination by brain MRI of children and dogs in Mexico City exposed to air pollution showed the prefrontal cortex as a potential target as white matter hyperintense lesions were found there (Calderón-Garcidueñas et al., 2008).

A study using animal as well as human models identified multiple potential pathways for damage to the brain and central nervous system (Block & Calderón-Garcidueñas, 2009), including neuroinflammation, altered immune system responses, aggregation of proteins, and the direct toxic effects of the pollutants themselves (Block & Calderón-Garcidueñas, 2009). Air pollutants are thought to increase proinflammatory signals in the body as a whole, eventually leading to inflammation in the brain and thereby also affecting the immune system (Block & Calderón-Garcidueñas, 2009). Inflammation and changes in immune system cells, such as microglia, can result in direct damage to brain tissue or damage to the blood-brain barrier, potentially making it easier for pollutants to enter and accumulate in the brain (Block & Calderón-Garcidueñas, 2009). In addition, these pollutants can have direct toxic effects on brain tissue. For example, ozone is a reactive oxygen species that can damage the brain by inducing oxidative stress (Block & Calderón-Garcidueñas, 2009). The presence of multiple mechanisms makes it difficult to determine which effect is most responsible for the damaging effects and underscores the need for further research in this area.
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Re: The role of air pollution in cognitive impairment and decline

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Breathing in Dirty Air During Pregnancy May Affect Children’s IQs

Sep 10, 2019


https://theswaddle.com/lower-iq-in-chil ... pregnancy/


Breathing in fine particles of pollution or soot-laden air during pregnancy may negatively affect children’s IQ, according to a new analysis published in Environmental Research.

The research assessed the relationship between air pollution and cognitive development among kids and concluded that children of mothers who were exposed to pollution from coal plants, burning fuel from cars and trucks, and airborne dust during pregnancy scored lower on IQ tests by 2.5 points compared to children of mothers who breathed in cleaner air.

Researchers studied a group of Tennessee-based women, monitoring them while they were pregnant. When their children turned 4 and 5, they were given an IQ test.

“[Fine particulate] pollution is less-studied as a neurodevelopment toxicant, so I think that makes it particularly interesting to have these results,” Catherine Karr, a study author and pediatric environmental medicine doctor at the University of Washington, told KQED.

“I think this work really highlights that low-level exposure might be dangerous and that we need to do more work to know what a safe level is,” Megan Herting, a neuroscientist at the University of Southern California who was not involved in the research, also told KQED.

The authors also found that good maternal nutrition cushions the impact of air pollution on children. Pregnant women are asked to eat folate-rich foods such as leafy vegetables and are also prescribed prenatal vitamins like folic acid. The researchers found that if pregnant women consumed less folate-rich foods and breathed in dirty air, their children’s scored about 7 points lower on IQ tests compared to children whose mothers ingested enough folate and also breathed dirty air.

Researchers say these findings can help pregnant women take stock of the environment they are in, and potentially adjust their folate intake accordingly.

Although various researchers worldwide are continuing efforts to study the connection between air pollution and its impact on brains, the current findings are particularly useful because as of today, 11 out of the 12 most polluted cities on a World Health Organization list are in India.

The Swaddle has also earlier reported a study that confirmed the presence of soot from air pollution in pregnant women’s placentas. “Air pollution has been linked to a host of health problems in recent years, from premature deaths in adults, to cognitive delays in kids, to asthma in both,” The Swaddle reported at the time.
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Re: The role of air pollution in cognitive impairment and decline

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Smog in our brains

Researchers are identifying startling connections between air pollution and decreased cognition and well-being.


July/August 2012

https://www.apa.org/monitor/2012/07-08/smog


That yellow haze of smog hovering over the skyline isn't just a stain on the view. It may also leave a mark on your mind.

Researchers have known since the 1970s that high levels of air pollution can harm both cardiovascular and respiratory health, increasing the risk of early death from heart and lung diseases. The effect of air pollution on cognition and mental well-being, however, has been less well understood.

Now, evidence is mounting that dirty air is bad for your brain as well.

Over the past decade, researchers have found that high levels of air pollution may damage children's cognitive abilities, increase adults' risk of cognitive decline and possibly even contribute to depression.

"This should be taken seriously," says Paul Mohai, PhD, a professor in the University of Michigan's School of Natural Resources and the Environment who has studied the link between air pollution and academic performance in children. "I don't think the issue has gotten the visibility it deserves."

Cognitive connections

Most research on air pollution has focused on a type of pollutant known as fine particulate matter. These tiny particles — 1/30th the width of a human hair — are spewed by power plants, factories, cars and trucks. Due to its known cardiovascular effects, particulate matter is one of six principal pollutants for which the Environmental Protection Agency (EPA) has established air quality standards.

It now seems likely that the harmful effects of particulate matter go beyond vascular damage. Jennifer Weuve, MPH, ScD, an assistant professor of internal medicine at Rush Medical College, found that older women who had been exposed to high levels of the pollutant experienced greater cognitive decline compared with other women their age (Archives of Internal Medicine, 2012). Weuve's team gathered data from the Nurses' Health Study Cognitive Cohort, a population that included more than 19,000 women across the United States, age 70 to 81. Using the women's address history, Weuve and her colleagues estimated their exposure to particulate matter over the previous seven to 14 years. The researchers found that long-term exposure to high levels of the pollution significantly worsened the women's cognitive decline, as measured by tests of cognitive skill.

Weuve and her colleagues investigated exposure to both fine particulate matter (the smallest particles, less than 2.5 micrometers in diameter) and coarse particulate matter (larger particles ranging from 2.5 to 10 micrometers in size).

"The conventional wisdom is that coarse particles aren't as important as fine particles" when it comes to human health, Weuve says. Previous studies in animals and human cadavers had shown that the smaller particles can more easily penetrate the body's defenses. "They can cross from the lung to the blood and, in some cases, travel up the axon of the olfactory nerve into the brain," she says. But Weuve's study held a surprise. She found that exposure to both fine and coarse particulate was associated with cognitive decline.

Weuve's results square with those of a similar study by Melinda Power, a doctoral candidate in epidemiology and environmental health at the Harvard School of Public Health. Power and her colleagues studied the link between black carbon — a type of particulate matter associated with diesel exhaust, a source of fine particles — and cognition in 680 older men in Boston (Environmental Health Perspectives, 2011). "Black carbon is essentially soot," Power says.

Power's team used black carbon exposure as a proxy for measuring overall traffic-related pollution. They estimated each man's black carbon exposure by cross-referencing their addresses with an established model that provides daily estimates of black carbon concentrations throughout the Boston area. Much like Weuve's results in older women, Power and colleagues found that men exposed to high levels of black carbon had reduced cognitive performance, equivalent to aging by about two years, as compared with men who'd had less black carbon exposure.

But while black carbon is a convenient marker of air pollution, it's too soon to say that it's what's causing the cognitive changes, Power says. "The problem is there are a lot of other things associated with traffic — noise, gases — so we can't say from this study that it's the particulate part of the air pollution that matters."

Still, the cumulative results of these studies suggest that air pollution deserves closer scrutiny as a risk factor for cognitive impairment and perhaps dementia.

"Many dementias are often preceded by a long period of cognitive decline. But we don't know very much about how to prevent or delay dementia," Weuve says. If it turns out that air pollution does contribute to cognitive decline and the onset of dementia, the finding could offer a tantalizing new way to think about preventing disease. "Air pollution is something that we can intervene on as a society at large, through technology, regulation and policy," she says.

Young minds

Research is also finding air-pollution-related harms to children's cognition. Shakira Franco Suglia, ScD, an assistant professor at Boston University's School of Public Health, and colleagues followed more than 200 Boston children from birth to an average age of 10. They found that kids exposed to greater levels of black carbon scored worse on tests of memory and verbal and nonverbal IQ (American Journal of Epidemiology, 2008).

More recently, Frederica Perera, DrPH, at the Columbia University Mailman School of Public Health, and colleagues followed children in New York City from before birth to age 6 or 7. They discovered that children who had been exposed to higher levels of urban air pollutants known as polycyclic aromatic hydrocarbons while in utero were more likely to experience attention problems and symptoms of anxiety and depression (Environmental Health Perspectives, 2012). These widespread chemicals are a byproduct of burning fossil fuels.

Meanwhile Mohai, at the University of Michigan, found that Michigan public schools located in areas with the highest industrial pollution levels had the lowest attendance rates and the greatest percentage of students who failed to meet state testing standards, even after controlling for socioeconomic differences and other confounding factors (Health Affairs, 2011). What's worse, the researchers analyzed the distribution of the state's public schools and found that nearly two-thirds were located in the more-polluted areas of their districts. Only about half of states have environmental quality policies for schools, Mohai says, "and those that do may not go far enough. More attention needs to be given to this issue."

Although Michigan and Massachusetts may experience areas of poor air quality, their pollution problems pale in comparison to those of Mexico City, for example. In a series of studies, Lilian Calderón-Garcidueñas, MD, PhD, a neuropathologist at the University of Montana and the National Institute of Pediatrics in Mexico City, has investigated the neurological effects of the city's infamous smog.

In early investigations, Calderón-Garcidueñas dissected the brains of dogs that had been exposed to air pollution of Mexico City and compared them with the brains of dogs from a less-polluted city. She found the Mexico City dogs' brains showed increased inflammation and pathology including amyloid plaques and neurofibrillary tangles, clumps of proteins that serve as a primary marker for Alzheimer's disease in humans (Toxicologic Pathology, 2003).

In follow-up research, Calderón-Garcidueñas turned her attention to Mexico's children. In one study, she examined 55 kids from Mexico City and 18 from the less-polluted city of Polotitlán. Magnetic resonance imagining scans revealed that the children exposed to urban pollution were significantly more likely to have brain inflammation and damaged tissue in the prefrontal cortex. Neuroinflammation, Calderón-Garcidueñas explains, disrupts the blood-brain barrier and is a key factor in many central nervous system disorders, including Alzheimer's disease and Parkinson's disease. Perhaps more troubling, though, the differences between the two groups of children weren't just anatomical. Compared with kids from cleaner Polotitlán, the Mexico City children scored lower on tests of memory, cognition and intelligence (Brain and Cognition, 2008).

Brain changes

It's becoming clearer that air pollution affects the brain, but plenty of questions remain. Randy Nelson, PhD, a professor of neuroscience at the Ohio State University, is using mouse studies to find some answers. With his doctoral student Laura Fonken and colleagues, he exposed mice to high levels of fine particulate air pollution five times a week, eight hours a day, to mimic the exposure a human commuter might receive if he or she lived in the suburbs and worked in a smoggy city (Molecular Psychiatry, 2011). After 10 months, they found that the mice that had been exposed to polluted air took longer to learn a maze task and made more mistakes than mice that had not breathed in the pollution.

Nelson also found that the pollutant-exposed mice showed signs of the rodent equivalent of depression. Mice said to express depressive-like symptoms give up swimming more quickly in a forced swim test and stop sipping sugar water that they normally find attractive. Both behaviors can be reversed with antidepressants. Nelson found that mice exposed to the polluted air scored higher on tests of depressive-like responses.

To find out more about the underlying cause of those behavioral changes, Nelson compared the brains of mice that had been exposed to dirty air with brains of mice that hadn't. He found a number of striking differences. For starters, mice exposed to particulate matter had increased levels of cytokines in the brain. (Cytokines are cell-signaling molecules that regulate the body's inflammatory response.) That wasn't entirely surprising, since previous studies investigating the cardiovascular effects of air pollution on mice had found widespread bodily inflammation in mice exposed to the pollution.

More surprisingly, Nelson also discovered physical changes to the nerve cells in the mouse hippocampus, a region known to play a role in spatial memory. Exposed mice had fewer spines on the tips of the neurons in this brain region. "Those [spines] form the connections to other cells," Nelson says. "So you have less dendritic complexity, and that's usually correlated with a poorer memory."

The changes are alarming and surprising, he says. "I never thought we'd actually see changes in brain structure."

Nelson's mice experienced quite high levels of pollution, on par with those seen in places such as Mexico City and Beijing, which rank higher on the pollution scale than U.S. cities. It's not yet clear whether the same changes would occur in mice exposed to pollution levels more typical of American cities. Another limitation, he notes, is that the animals in his study were genetically identical. Nelson says he'd like to see similar studies of wild-type mice to help tease out whether genetic differences might make some people more or less vulnerable to the effects of pollution. "I would suspect there are people who are wildly susceptible to this and people who are less so, or not at all," he says.

Few studies have investigated connections between depression and air pollution, but Nelson's wasn't the first. A study by Portuguese researchers explored the relationship between psychological health and living in industrial areas. They found that people who lived in areas associated with greater levels of air pollution scored higher on tests of anxiety and depression (Journal of Environmental Psychology, 2011).

Back in Ohio, Nelson plans to study how much — or how little — pollution is necessary to cause changes in the brain and behavior. He's also beginning to look at the effects of air pollution on pregnant mice and their offspring. Though more research is needed to fully understand how dirty air impairs the brain, he says, the picture that's emerging suggests reason for concern.

In the United States, the Environmental Protection Agency reviews the scientific basis for particulate matter standards every five years or so, and completed its last review in 2009.

To date, the EPA hasn't factored psychological research into their standards assessments, but that could change, according to a statement the EPA provided to the Monitor. "Additional research is necessary to assess the impact of ambient air pollutants on central nervous system function, such as cognitive processes, especially during critical windows of brain development. To this end, as the number of … studies continue to increase and add to the weight of overall evidence, future National Ambient Air Quality Standards assessments will again assess and address the adequacy of existing standards."

In the meantime, says Weuve, there's not much people can do to protect themselves, short of wearing special masks, installing special filtration systems in their homes and offices or moving to cities with less airborne pollution. "Ultimately, we're at the mercy of policy," she says.

The good news, Nelson says, is that the mental and cognitive effects of air pollution are finally beginning to receive attention from the mental health research community. "We sort of forget about these environmental insults," says Nelson. "Maybe we shouldn't."
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