Air pollution, Alzheimer’s disease, Cognitive decline

Exposure to Fine Particulates Worsens Episodic Memory, A Marker of Alzheimer’s Disease

By Jacob Schor ND, FABNO

In his 2015 novel, The Buried Giant, Kazuo Ishiguro tells the story of a civilization reminiscent of England during the Dark Ages. All the characters in the book suffer from worsening amnesia caused by mists, which we eventually come to learn are being generated by the breath of a dragon. Did that need a spoiler alert? Too late now.

I am reminded of this story by several recent papers on fine particulate air pollution, cognitive decline, and the risks of developing Alzheimer’s disease. In recent years multiple studies have reported that fine particulate air pollution negatively impacts various aspects of health. By fine particulates, we mean the super tiny particles, those less than 2.5 micrograms in size. It turns out that these are the most harmful of all the tiny bits of stuff floating in the air. They are too small for the lung cilia to expel and so they end up absorbed into the bloodstream floating about and instigating inflammation and causing damage throughout the body.

The study that got me started on this Alzheimer’s thing was conducted by Younan et al and was published just in November 2019.¹

Knowing that a decline in episodic memory is a preclinical symptom of Alzheimer’s disease, the authors compared memory function to fine particulate exposure. They asked whether exposure to fine particulates (PM2.5) was associated with decline in episodic memory and whether the structural changes seen in the brain after exposure are indicative of early disease. This research was conducted on 998 women ages 73 to 87 who were free of dementia, periodically giving them tests assessing learning and memory.

The women underwent annual episodic memory assessment using the California Verbal Learning Test, including measures of immediate free recall/new learning and delayed free recall (short- and long-delay). In addition to memory testing, magnetic resonance imaging (MRI) was used to detect brain atrophy, or wasting; and participant brain deterioration was scored on its degree of similarity to the atrophy characteristic of Alzheimer’s disease. Environmental Protection Agency (EPA) data on air pollution at the women’s home addresses was used to gauge fine particulate exposure for the three years prior to their first brain MRI. This allowed assessment of exposure to fine particulates (PM2.5) and association between memory decline and changes in brain structure. This was one large, comprehensive, and carefully done study.

The authors report that the greater the exposure to PM2.5_, the greater the declines in immediate recall and new learning the women showed on testing. For each jump of 2.81 μg/m³ in fine particulate exposure, the annual rate of decline accelerated by between 15% to 19.3%. Long-term exposure was associated with greater Alzheimer’s disease pattern similarity scores. Let me say that simpler. The more bad stuff the women had breathed, the more their brains looked like they were developing Alzheimer’s. Fine particulates caused neurotoxicity that contributes to early decline of the ability to recall recent things or learn new information. This fuzziness of thought was associated with atrophy of the brain’s grey matter and an increased Alzheimer’s disease risk down the road. We have our own mist-breathing dragon wiping our memories away in the real world.

This isn’t new but it certainly sounds like bad news. The more research we see on fine particulate air pollution the worse it looks. Research published in June 2019 already suggested that long-term exposure to air pollution was associated with lower scores on tests of mental acuity. Shehab and Pope had measured fine particulate exposure in people who commute to work by traveling outdoors and demonstrated this was associated with significant declines in short-term cognitive function. Their results suggested that people living in the more polluted cities will have worse cognitive abilities on average than they might have if the air was cleaner.² Bottom line, from both the study by Younan et al and this earlier research, is that fine particulate exposures cause physiologic changes in the brain now linked to Alzheimer’s disease development. Younan et al found that the greater the women’s exposure to PM2.5, the lower their scores on the cognitive tests. The MRI results showed that increased exposure to fine particulates was associated with increased brain atrophy, even before clinical symptoms of dementia had appeared. The more pollution, the more their brains looked like they had Alzheimer’s disease.^3,4

In October 2019, a meta-analysis by Tsai et al concluded that fine particulate exposure is a potential determinant of Alzheimer’s disease. Their data revealed that an exposure increase of 10 μg/m³ in PM2.5 was significantly and positively associated with dementia, more than tripling risk (HR = 3.26, 95% CI: 1.20, 5.31).⁵

We ought to make a bigger fuss when our patients complain about poor memory or have a family history worrisome of neurodegeneration and directly inquire about air quality and the patient’s exposure to fine particulates. We may not yet know if reducing particulate exposure will lead to improvement, but we can certainly assume that worsening exposure will worsen symptoms and doing nothing won’t help.

The EPA considers the upper limit of “good quality” air to be 12 micrograms per cubic meter (µg/m³). Here in Denver, our worst air quality day last year, reached 57 µg/m³. Seattle’s worst was 47 µg/m³. San Francisco topped out at 200 µg/m³ . This is nothing though. On one day in November 2019, New Delhi’s air reached over 900 µg/m³, blasting past the EPA’s definition of “hazardous” air (which maxes out at 500) and into unknown territory. Recall that in the study, a 2.8 μg/m³ difference in PM2.5 exposure was associated with a nearly 20% acceleration in annual decline rate of cognitive function.

You can check your own outdoor air quality right now at this website administered by the EPA: https://www.airnow.gov.

Or generate a report on air quality exposure by location at https://www.epa.gov/outdoor-air-quality-data/air-quality-statistics-report.

In 2015 particulate pollution was responsible for an estimated 4.2 million deaths worldwide. The majority of these deaths were in Asia. Even though the United States has some of the cleanest air in the world, fine particulates are thought to have contributed to 88,000 premature deaths in 2015. This makes air pollution more deadly than diabetes. Air quality in the US had steadily improved for many years but, since 2016, air in the United States has worsened; fine particulates have increased on average by over 5%.⁶ It has been suggested that this downturn resulted from lax enforcement of the Clean Air Act by the EPA.

The Environmental Protection Agency calculates that the reduction in fine particulates achieved in the past saved hundreds of thousands of lives.⁷ These calculations come in part from a number of unique studies published over the years in which air quality changed dramatically in specific locations allowing the measurement of benefit and then extrapolation to larger populations. A December paper published in the Annals of the American Thoracic Society summarized some of these cases. What stands out in all of these studies is how rapidly the benefits were seen.⁸

Starting just a week after a ban on smoking in Ireland went into effect in March 2004, all-cause mortality in the country dropped by 13%. There was also a 26% reduction in ischemic heart disease, a 32% reduction in stroke, and a 38% reduction in COPD.⁹

In the United States, during the late 1980s when a steel mill in Utah closed for 13 months, hospitalizations for pneumonia, pleurisy, bronchitis, and asthma dropped by half. School absenteeism decreased by 40% and daily mortality fell by 16% for every 100 µg/m³ PM10 (a larger sized pollutant) decrease.¹⁰

When the 1996 Olympic Games were held in Atlanta, Georgia, parts of the city were closed to traffic to relieve congestion so that athletes could arrive at their venues on time. This strategy also reduced air pollution in the city. In the following weeks, medical visits by children for asthma treatment dropped by more than 40% and trips to emergency departments dropped by 11%. Asthma hospitalizations decreased by 19%.¹¹

Something similar occurred when China imposed factory and travel restrictions during the 2008 Beijing Olympics; lung function improved with a 46% reduction in asthma-related physician visits and less cardiovascular mortality.¹²

In Nigeria, when families were given clean ethanol cook stoves that reduced indoor air pollution, pregnancies ended with higher birthweights, greater gestational age at delivery, and less perinatal mortality.¹³

The Thoracic Society report also analyzed the cost of implementing the Clean Air Act. Twenty-five years after Richard Nixon signed the Clean Air Act into law, the health benefits exceed the cost of implementation by a ratio of 32:1 saving our country an estimated 2 trillion dollars. The Clean Air Act is one of the most effective public health policies ever enacted in the United States. Emissions of the major pollutants were reduced by 73% between 1990 and 2015 while the US gross domestic product grew by more than 250%.

Recent research such as this paper by Younan et al linking fine particulate air pollution to Alzheimer’s disease suggests that the EPA’s cost benefit analysis may actually be wrong. The cost of Alzheimer’s disease and potential savings from reducing air pollution were not considered. Air pollution may cause more morbidity and mortality than previously thought and so may cost more than the EPA has estimated. Data have not taken into account the cost of decreasing cognitive function. This, of course, is a fancy way of saying getting dumber. The cost of people being dumber than they need be may eventually turn into the greatest of the dangers associated with fine particulates.

Update: This article was originally written in the autumn of 2019, before we had any inkling of the many changes the future had in store for us. The global response to the COVID-19 pandemic caused dramatic decreases in air pollution. A July 2020 report tells us that in regions of China, PM2.5 concentrations fell an average of 18.57 to 25.00 μg/m3 depending on time of day and weather conditions. The greatest decrease was in Hubei, with a 27 ug/m3 drop.¹⁴ In Wuhan, PM2.5 levels dropped nearly 37%.¹⁵ Particulate levels also dropped in the US especially in urban areas though these drops varied by how complete a lockdown was instituted.¹⁶

Full analysis of how these shifts influenced morbidity and mortality have yet to be published. Yet we are seeing alarming hints. A paper from Francesca Dominici’s team at Harvard looked at COVID-19 mortality rates and air pollution but as of this writing is still in preprint. Their team collected COVID-19 death counts from more than 3,000 counties in the United States (representing 98% of the population) up until April 22, 2020. When these rates were compared to long-term levels of PM2.5 exposure, their analysis revealed “…that an increase of only 1 μg/m3 in PM2.5 is associated with an 8% increase in the COVID-19 death rate…. The results were statistically significant and robust to secondary and sensitivity analyses.”¹⁷ These are sobering numbers if they prove to be accurate over time.

Much more focus needs to be placed on recognizing the important role that common air pollutants hold in health, with commensurate actions being taken to reduce the levels of common air pollutants in the home—the one environment most people are in control of. It is quite possible that one of the most effective preventive medicine modalities would be the installation of a high-quality air purifier in the home. –Walter Crinnion, ND