POLICY BRIEF | NOVEMBER, 2019 To reduce Alzheimer’s disease, clean up the air By Jonathan D. Ketcham KEY TAKEAWAYS Alzheimer’s disease and related forms of dementia are devastating, irreversibly robbing people of their ability to care n Research indicates that tiny airborne particulates of diesel for themselves, recognize family and friends, and understand exhaust, organic compounds, the world around them. These illnesses are also widespread. ash, and similar materials— Figure 1 shows that their prevalence climbs sharply with age, known as PM2.5—can cause Alzheimer’s disease and afflicting over a third of those above age 80 in the U.S. related dementias. Because of its severity and prevalence combined with the aging of the U.S. population, the Centers for Disease Control has labeled dementia as a public n A 15-year nationwide study health crisis. Over 5 million dementia patients in the U.S. spent $277 billion of Medicare beneficiaries on health care. And the cost doesn’t end there. In addition to the years and estimates that federal quality of life lost by those with the disease, millions of family members and standards limiting airborne others spend valuable time and effort caring for them. PM2.5 levels led to 182,000 The causes of dementia are not well understood. But medical research fewer Alzheimer’s cases in suggests that air pollution may play a role even though the precise biological 2013, producing $214 billion in pathways remain unknown. benefits. Prior research indicates that long-term exposure to higher concentrations of n Despite the lack of medical airborne particles smaller than 2.5 microns in diameter (PM2.5 )—about 1/30th treatment for dementia, of the width of a human hair—is associated with higher rates of Alzheimer’s additional technological and dementia diagnoses. For example, a study in London found a positive innovation and environmental association between a neighborhood’s PM2.5 levels and the prevalence regulations can reduce its of dementia (Carey et al. 2018). Medical research has also found that tiny prevalence by improving air particles of materials such as ash, industrial waste, and diesel exhaust quality. build up in the brain and cause inflammation, but the link between this and Alzheimer’s disease remains uncertain (Maher et al. 2016; Underwood 2017). My Arizona State University colleagues Kelly Bishop and Nicolai Kuminoff and I recently carried out the first large-scale nationwide study designed to evaluate whether PM2.5 increases the prevalence of dementia (Bishop et al. 2019). Our research tracks the health and residential locations of more than a John A. and Cynthia Fry Gunn Building siepr.stanford.edu 366 Galvez Street, Stanford, CA 94305-6015 @siepr facebook.com/SIEPR/ 1 POLICY BRIEF | NOVEMBER, 2019 Figure 1 60% People Diagnosed with Dementia 50% female male 40% 30% 20% 10% 0% 66 69 72 75 78 81 84 87 90 93 96 Age million people on Medicare over 15 years and is designed were subject to additional regulations, accelerating the to isolate the effects of PM2.5 from spurious correlations improvement in air quality in some neighborhoods more that may arise for reasons other than pollution exposure than others. causing dementia. We estimate that as a result of these regulations The results are clear: Long-term exposure to PM2.5 specifically, the U.S. had 182,000 fewer cases of substantially increases a person’s risk of developing dementia in 2013, with a value of this reduced dementia Alzheimer’s disease and related dementia. We estimate estimated at $214 billion. We also find evidence that that a 10 percent increase in average PM2.5 exposure further tightening the EPA’s PM2.5 standards would over a decade boosts the probability of developing reduce dementia rates even more. Alzheimer’s or related dementias by around 8 percent, or 1.7 percentage points. This is equivalent to the A natural experiment increase in risk associated with a woman aging from 75 Our study is based primarily on three sources of data: (1) to 76.5 and is about twice as large as the increased risk EPA measurements of PM2.5 concentrations from 1,900 associated with having hypertension, a previously known monitors across the country; (2) 15 years of records of risk factor for dementia. Medicare beneficiaries from the U.S. Centers for Medicare These results mean that the benefits of improving air and Medicaid Services (CMS), including demographic quality are greater than previously known. The good information, addresses, and medical records for news is that during our study period of 1999 to 2013, each year; and (3) U.S. Census data on neighborhood Americans age 65 and over experienced a 40 percent characteristics. average reduction in the PM2.5 levels at their homes. We start with a random sample of 10 percent of all These gains were due to improvements in technology, Medicare beneficiaries. We feature results from an people moving to cleaner neighborhoods, and stricter analysis of 1.26 million people who were on traditional regulation by the Environmental Protection Agency Medicare in 2013 and did not have dementia in 2004. (EPA). The EPA began regulating counties’ PM2.5 levels in When we include those who died between 2004 and 2004, setting a threshold of 15.05 micrograms per cubic 2013 or include those who were on managed-care plans meter. Counties that failed to meet these standards John A. and Cynthia Fry Gunn Building siepr.stanford.edu 366 Galvez Street, Stanford, CA 94305-6015 @siepr facebook.com/SIEPR/ 2 POLICY BRIEF | NOVEMBER, 2019 Figure 2 20 Nonattainment counties Mean of Average Readings (microgram per cubic meter) 18 Attainment counties 16 Difference 14 12 10 8 6 4 2 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 known as Medicare Advantage, our results show even for those living in places that met the EPA’s standards. larger effects of PM2.5 on Alzheimer’s and dementia than Furthermore, the reductions differed even within the what we report here. nonattainment counties, because regulators focused their efforts on specific polluters and neighborhoods. We use 2004 as the baseline year because that is when the EPA started enforcing its PM2.5 standards. Because We leverage these differences in the reduction in PM2.5 the EPA’s enforcement affected places differently, it over the subsequent decade due to the regulation to created a special opportunity to disentangle the effects isolate how PM2.5 affects the probability of developing of air pollution on dementia from the effects of other dementia. By combining our rich data from CMS and risk factors that may be associated with how much the U.S. Census with the variation in pollution exposure air pollution people breathe, for example due to their over the decade due to the EPA’s regulation, our study choices about where to live. accounts for the influence of confounding factors. For example, our approach rules out that the observed At the beginning of 2005, the EPA designated 132 relationship between air pollution and dementia might counties in 21 states as “nonattainment” areas, meaning arise solely because sicker or poorer people may be more that air quality monitor readings in them showed likely to live in heavily polluted areas. that PM2.5 concentrations were above the permitted levels. Local regulators were then required to reduce Our study capitalizes on the EPA regulation causing concentrations in those counties and could be penalized differences in the change in pollution over the decade if they failed to do so. experienced by people of the same age, race, and gender who lived in the same area and who, at the start of the In the following years, PM2.5 levels dropped faster in the decade, had received the same medical diagnoses for nonattainment counties. Figure 2 shows that for the dementia risk factors, had the same level of gross annual Medicare population in nonattainment counties, average medical expenditures, and lived in neighborhoods PM2.5 concentrations over the next decade fell by nearly with the same levels of PM2.5 from 2001 to 2003 and 10 percent (1.24 micrograms per cubic meter) more than John A. and Cynthia Fry Gunn Building siepr.stanford.edu 366 Galvez Street, Stanford, CA 94305-6015 @siepr facebook.com/SIEPR/ 3 POLICY BRIEF | NOVEMBER, 2019 with similar distributions of race, income, educational Medical science has not yet established precisely how attainment, and property values. small particulates contribute to dementia, and it may be that only certain types and sources of pollution Our main result is that a one microgram per cubic meter are the culprits. Such knowledge will help us to better increase in average particulate matter concentrations focus on the technology and regulations that will most over 10 years raises the probability of developing effectively improve the quality of our air and ultimately dementia by 1.68 percentage points. Furthermore, we our cognitive health and well-being in old age. observe this effect even at levels below the EPA’s current regulatory threshold, which was set at 12 micrograms References per cubic meter in 2012. To put this in perspective, a decade of breathing air with a one microgram per cubic Bishop, Kelly C., Ketcham, Jonathan D., Kuminoff, Nicolai V., “Hazed and Confused: The Effect of Air Pollution on Dementia,” NBER Working Paper meter higher concentration is equivalent to inhaling an 24970, 2019. additional 4 percent of an aerosolized paperclip made of Carey, I.M., Anderson, H.R., Atkinson, R.W., Beeves, S.D., Cook, D.G., arsenic, lead, mercury, and nickel and other materials. Strachan, D.P., Dajnak, D., Gulliver, J., and Kelly, F.J., “Are Noise and In the context of our study, this change in concentration Air Pollution Related to the Incidence of Dementia? A Cohort Study in is modest, equal to less than 10 percent of the average London, England,” BMJ Open, 2018, e022404. person’s levels during our study period. Maher, Barbara A., et al., “Magnetite Pollution Nanoparticles in the Human Brain,” Proceedings of the National Academy of Sciences, 2016, The federal government is required to conduct a cost- 113(39), 10797-10801. benefit analysis of environmental regulations. Our study Underwood, Emily, “The Polluted Brain,” Science, 2017, 355(6323), 342-345. shows that the existing analysis underestimates the benefits of the PM2.5 regulations because the effects of air pollution on dementia were previously unknown. By Jonathan Ketcham is a Visiting combining our results with Census data on the elderly Professor at SIEPR. He is the Earl G. population living in nonattainment counties, we estimate and Gladys C. Davis Distinguished that the regulations led to a 2.1 percentage point lower Research Professor in Business in dementia rate in those counties, amounting to 182,000 the W.P. Carey School’s Department fewer people with dementia in 2013. Using conventional of Marketing and Department of Economics at assumptions about the value of life and health, we Arizona State University. He conducts econometric calculate that this is worth around $214 billion. studies of the roles of incentives and information in health care markets. Conclusion Even while we wait for the development of medical treatments to prevent Alzheimer’s and related dementias, our research indicates that improving our The Stanford Institute for Economic Policy air quality now—and reducing small particulate matter Research (SIEPR) catalyzes and promotes evidence- specifically—will reduce the burden of dementia. based knowledge about pressing economic issues, leading to better-informed policy solutions Our research finds that the EPA’s rule requiring PM2.5 for generations to come. We are a nonpartisan concentrations to remain below 15 micrograms per cubic research institute, and SIEPR Policy Briefs reflect meter reduced dementia’s prevalence in the U.S. We also the views and ideas of the author only. find evidence that the lower threshold implemented in 2012 will contribute to lower rates of dementia. John A. and Cynthia Fry Gunn Building siepr.stanford.edu 366 Galvez Street, Stanford, CA 94305-6015 @siepr facebook.com/SIEPR/ 4