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Wang B, Eum KD, Kazemiparkouhi F, et al. The effects of long-term PM2.5Exposure to specific causes of death: exposure-response curves and effect modification in 53 million US Medicare beneficiaries.Environmental health. 2020;19(1):20.
Draft
observation. The researchers used hybrid machine learning and Cox proportional hazards models to assess the association of long-term exposure to particulate matter2.5(Particulate matter with a width of 2.5 micrometers or less) with certain causes of death.
Participant
Fifty-three million (53,000,000) US Medicare beneficiaries (aged ≥65 years) from 2000 to 2008 with approximately 4 billion person-months of follow-up.
pollution
The researchers calculated PM exposure2.5through a combination of Environmental Protection Agency (EPA), meteorological and geo-temporal models applied to each participant's address and zip code.
Target parameters
Disease-specific and all-cause mortality.
Key insights
PM2.5has been associated with increased mortality from cardiovascular disease (CVD), respiratory disease and cancer (except lung cancer). A 10 μg/m3Increase in average PM2.5in the 12 months before death was associated with a 5% increase in all-cause mortality, as well as an 8.8% increase in all-cause cardiovascular mortality, a 5.6% increase in all-cause respiratory mortality, and a 2.5% increase in all cancer-related deaths in models adjusted for age, sex, race, zip code, and socioeconomic status (SES). PM2.5However, exposures were not associated with lung cancer mortality. The results were not sensitive to controls for ozone pollution. PM2.5-Mortality associations for cardiovascular and respiratory causes were positive and significant for beneficiaries regardless of sex, race, age, SES, and urbanicity, with no evidence of a lower threshold for response or lower risk ratios (RRs) with low PN2.5levels. Associations between PM2.5and cardiovascular and respiratory mortality were linear and higher for younger, black, and urban beneficiaries, but were broadly similar by SES.
Practice implications
This study, along with the recent meta-analysis by Pranata et al.1was particularly relevant as we found ourselves in a lockdown response to the Covid-19 pandemic.2The mandated socially distanced response to the pandemic had a notable side effect: global air pollution dropped dramatically worldwide.
The result is that we have become participants in a global experiment, a global cohort testing whether lower air pollution is associated with improved health, lower morbidity and a reduction in mortality, particularly from cardiovascular disease. Air pollution fell dramatically as every country implemented lockdown measures to slow the spread of Covid-19.3
The work of Pranata et al. was published on March 13, 2020Journal of Evidence-Based Medicine. It is a comprehensive review and meta-analysis of previous studies on air pollution and cardiovascular disease mortality. Data from 84 cohorts with a total of 28,215,394 subjects were combined. Increases in particulate matter air pollutants were associated with increases in all measures of CVD, acute coronary events, stroke, and hypertension. CVD mortality rates increased by 10% for PM2.5increased and 17% when the larger PM10Particles were tracked. Elevations in nitric oxide (NO) are associated with a 17% increase in cardiovascular mortality and a 23% increase in all-cause mortality.3Both of these 2 recent papers are suitable candidates for review.
Air pollution fell dramatically as every country implemented lockdown measures to slow the spread of Covid-19.
Also worth mentioning is a paper by Hayes et al. from July 2019, which reported that 10 μg/m each3Increase in PM2.5was associated (in fully adjusted models) with a 16% increase in ischemic heart disease mortality (hazard ratio [HR], 1.16; 95% CI, 1.09-1.22) and a 14% increase in stroke mortality (HR: 1.14; 95% CI: 1.02-1.27).4Any of these papers would be enough to predict that the decline in air pollution as a result of the response to Covid-19 could influence current disease rates.
Wang et al.'s finding that lung cancer mortality was not associated with air pollution was not unexpected. Previous studies have also reported a similar null effect,5although others have seen a positive association.6
The range of predicted numbers of deteriorating air quality that we find in this brief review ranges from a 5% increase in all-cause mortality (Wang et al.), to a 10% increase in cardiovascular mortality (Pranata et al.), to a 16% increase in mortality from ischemic heart disease (Hayes et al.). Although several years older, the study by Pope et al. in 2015 that a similar increase in particulate matter concentrations was associated with a 12 percent increase in CVD deaths.7
These results provide a guide to estimate what we might see in future statistics looking back at this period in terms of cardiovascular mortality.
In an article published on the academic website G-Feed in early March, Marshall Burke, a professor in Stanford's Earth System Science Department, calculated that reduced air pollution in China last winter may have saved 20 times more lives in China than were lost due to the infection in that country.8Burke based his calculation on older Chinese research; Neither Pranata's nor Wang's results had been published when he made his calculations.9
Burke used the results of Su et al. from 2016 and data collected during the 2008 Summer Olympics and Paralympics. Recall how China made great efforts to reduce air pollution during the Games by restricting traffic.10Burke estimated this to be “approximately 10 ug/m3Reduction in particulate matter pollution across China in January-February 2020 compared to the same months in the previous two years.” Guojun He et al. had reported “that a 10% reduction in concentrations reduces the monthly standardized all-cause mortality rate by 8%.”11
Burke writes: “Putting these numbers together… there is a very large reduction in premature mortality… I calculate that you have 10 ug/m for 2 months3Reducing PM2.5likely saved the lives of 4,000 children under 5 and 73,000 adults over 70 in China.”
The US started with much cleaner air than China, so these relationships may not apply. However, as mentioned earlier, Wang et al. “no evidence of a lower threshold for response or lower risk ratios (RRs) at low PM2.5Levels.” This suggests that reducing our own pollution levels can still lead to significant improvements.
Approximately 647,000 people die from CVD in the United States each year.12If staying at home reduced that number by 10% (a conservative estimate), it would prevent nearly 65,000 deaths from cardiovascular disease alone, a change that would be noticeable. The decline of Pranata et al. by 16% would mean over 103,000 lives saved.
In previous editions ofNMJWe reviewed numerous studies that have associated PM2.5Exposure to various measures of health and disease. In the coming months and years, we may see more precise measurements of the true impact of air pollution and perhaps be able to more accurately calculate its cost to community health.
Unfortunately, our experiment may be confounded by other simultaneous events. The EPA is currently rolling back pollution enforcement regulations, and it can be difficult to account for the harm these rollbacks can cause when weighed against the health improvements from cleaner air. Job loss and the associated changes that unemployment has on the impact on heart health also need to be considered.
As we hunkered down during stay-at-home orders, a second unplanned experiment related to climate change was taking place. CO2 emissions have fallen dramatically. An abrupt halt to Chinese industrial production appears to have cut its carbon emissions by 25% earlier this year.13Whether this effect lasts long enough to be measured or is buried under the impact of stimulus packages that favor fossil fuel use remains to be seen.
Time will tell, but in the meantime, those of us who live in urban areas can enjoy cleaner air and clearer skies, even if it was just from our front porch and back patio.