Di Q, Dai L, Wang Y, et al. Association of short-term exposure to air pollution with mortality in older adults. JAMA. 2017;318(24):2446-2456.
To examine if fine particulate matter and ozone levels below current US national air quality standards increase the risk of death in older adults.
In order to estimate a possible association, the study employed case-crossover design and conditional logistic regression using a 2-pollutant model of warm-month ozone (April to October each year) and short-term exposures to fine particulate matter (PM2.5).
The study participants were all Medicare subscribers (generally over 65 and/or disabled), representing the entire US Medicare population from 2000 thru 2012. During the 13 years covered by the study, participants lived in almost 40,000 zip code–specific communities. Twenty-two million deaths were included in the regression data set. Subgroups for nonwhite, older than age 85, Medicaid-eligible, and age 75 and older were correlated with the pollutants as well.
Study Parameters Assessed
Daily exposures were assessed by zip code using estimates based on published and validated air pollution prediction models relying on land use, chemical transport modeling, and satellite remote-sensing data. This was useful in approximating daily exposures in rural areas not otherwise directly monitored. Ozone concentrations, PM2.5 concentrations, and death rates were examined to elucidate exposure-response relationships.
There was a statistically significant association between increased mortality and the short-term increase of 10 μg/m3 in PM2.5 (adjusted by ozone) and 10 ppb (parts per billion; 10−9) in warm-season ozone (adjusted by PM2.5) levels. With day-to-day increases of 10 μg/m3 in PM2.5, there was a 1.05% increase in deaths. For each 10−9 increase in ozone, there was a 0.51% increase in deaths. Disturbingly, there was no threshold of exposure to either compound considered safe.
Commenting on this study in an interview with the New York Times, coauthor Joel D. Schwartz, a professor of epidemiology at Harvard, stated, “This translates to PM2.5 causing an extra 20,000 deaths a year. Separately, a 10 parts per billion decrease in ozone would save 10,000 lives per year.”1
Although the Clean Air Act requires that the National Ambient Air Quality Standards (NAAQS) be evaluated every 5 years, prior to this study very little had been known about death rates relative to pollution levels below the NAAQS in susceptible population groups. This study reveals the increased health risks associated with below-standard levels of PM2.5 and ozone pollution, suggesting the need to re-evaluate current NAAQS. The study is particularly impressive, given the large cohort of older participants and the size of the geographic area covered, including previously unmonitored rural regions.
This study reveals the increased health risks associated with below-standard levels of PM2.5 and ozone pollution, suggesting the need to re-evaluate current NAAQS.
Information of this nature would be useful to communicate (similar to daily weather reports) to the general population, particularly in more densely populated, even mildly polluted areas. Because we know that air quality is associated with increased mortality, we must educate our most vulnerable members of society, such as the elderly and those suffering from cardiovascular disease, about the increased health risks of ozone and particulate matter.
Low-cost, personalized interventions such as face masks,2 air purifiers, supplementation with antioxidants, and supportive lifestyle measures to protect from cardiovascular events would be indicated3 since many cardiac deaths are related to ambient PM2.5-induced health effects. Heart attacks, strokes, heart failure, arrhythmias, and cardiac death all increase with just short-term increases in the level of ambient air small particulates.4 The mechanisms postulated for these effects include systemic inflammation, altered autonomic cardiac function, and an increase in atherosclerotic plaque formation. The effects were found to be additive in smokers vs nonsmokers, most likely due to chronic pulmonary inflammation.6
Plant-based dietary emphasis, exercise, stress management, and smoking cessation may help reverse cardiovascular atherosclerotic disease in as little as a year.5,6
On the other side of the age continuum, a Chinese study of college students recently looked at metabolic effects such as higher blood pressure, hormone levels, insulin resistance, and biomarkers of oxidative stress and inflammation among students exposed to higher PMs. The authors observed between-treatment differences in glucose, amino acids, fatty acids, and lipids. The biomarkers induced by PM2.5 were found to impact stress hormones: cortisol, cortisone, epinephrine, and norepinephrine. These findings may explain the mechanism behind the adverse health outcomes. Notably, when air purifiers were employed the levels of stress hormones were significantly reduced.7