From the Journals

Impact of climate change on mortality underlined by global study

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Action against climate change now helps our health today

The negative effects of climate change on global public health are already playing out around us, but scientific research shows that they will only get worse – unless we begin addressing the issue in earnest now.

At the macro level nationally, effective policy is actually being stripped away right now. “[While] scientists tell us we have little time to wait if we hope to avoid the most devastating effects of climate change, leaders in Washington, D.C., are attacking science and rolling back Obama-era rules from the Environmental Protection Agency,” such as working to weaken vehicle fuel-efficiency standards, relaxing methane emissions rules, ending mercury emissions regulation and taking other actions that will only increase air pollution.

“If these EPA rollbacks are successful, they will diminish our ability to mitigate health effects and diseases related to the burning of fossil fuels and the immense toll they take on our families. ... If we stop supporting and listening to the best available science, if we allow more pollution to be emitted, and if we start limiting the EPA’s ability to monitor and enforce pollution standards, then we put at risk everyone’s health – and especially the health and future of our children.”

Engaging in advocacy and communicating to our representatives that we want stronger regulations is one way people can personally take action, but we can take immediate actions in our everyday lives too. Rather than dwelling on the despair of helplessness and hopelessness that grips many people when it comes to climate change, this moment can be reframed as an opportunity for people to make decisions that immediately begin improving their health — and also happen to be good for the planet.

“To me, the most urgent challenge when it comes to health and climate change is the reality that, when climate change comes up, in the U.S. audience, the first thing that should come into people’s minds is that we need to do this now because we need to protect our children’s health. ... Too many people either don’t get that it matters to health at all, or they don’t get that the actions we need to take are exactly what we need to do to address the health problems that have been nearly impossible to deal with.”

For example, problems like rising child obesity and type 2 diabetes rates have plagued public health, yet people can make changes that reduce obesity and diabetes risk that also decrease their carbon footprints, he said. “One of the best ways to deal with obesity is to eat more plants, and it turns out that’s really good for the climate” Additionally, getting people out of cars and walking and cycling can reduce individuals’ risk of diabetes – while simultaneously decreasing air pollution. “We need to be doing these things regardless of climate change, and if parents and children understood that the pathway to a healthier future was through tackling climate change, we would see a transformation.”

The value of local policy actions should be emphasized, such as ones that call for a reduction in a city’s use of concrete – which increases localized heat – and constructing more efficient buildings. Healthcare providers have an opportunity – and responsibility – not only to recognize this reality but to help their patients recognize it too.

“We can also use our roles as trusted advisers to inform and motivate actions that are increasingly necessary to protect the health of the communities we serve.” They also need to be vigilant about conditions that will worsen as the planet heats up: For example, medications such as diuretics carry more risks in higher temperatures, and patients taking them need to know that.

The need to address climate change matters because we face the challenge of protecting the world’s most vulnerable people.

“One of the great things about climate change is if it causes us to rethink about what we need to do to protect the future, it’s going to help our health today. ... If we can use that as the motivator, then maybe we can stop arguing and start thinking about climate as a positive issue, as a more personal issue we can all participate in and be willing to invest in.”

Gina McCarthy, MS, was administrator of the Environmental Protection Agency during 2013-2017, and Aaron Bernstein, MD, MPH, is a pediatrician at Boston Children’s Hospital. Both are from the Center for Climate, Health, and the Global Environment (Harvard C-CHANGE) at the Harvard T.H. Chan School of Public Health in Boston. Their comments came from their perspective (N Engl J Med. 2019 Aug 22. doi: 10.1056/NEJMp1909643) published in NEJM along with this article and editorial and a phone interview. They reported not having any disclosures.



Regardless of where people live in the world, air pollution is linked to increased rates of cardiovascular disease, respiratory problems, and all-cause mortality, according to one of the largest studies ever to assess the effects of inhalable particulate matter (PM), published Aug. 21 in the New England Journal of Medicine.

“These data reinforce the evidence of a link between mortality and PM concentration established in regional and local studies,” reported Cong Liu of the Huazhong University of Science and Technology in Wuhan, China, and an international team of researchers.

“Many people are experiencing worse allergy and asthma symptoms in the setting of increased heat and worse air quality,” Caren G. Solomon, MD, of Harvard Medical School, Boston, said in an interview. “It is often not appreciated that these are complications of climate change.”

Other such complications include heat-related illnesses and severe weather events, as well as the less visible manifestations, such as shifts in the epidemiology of vector-borne infectious disease, Dr. Solomon and colleagues wrote in an editorial accompanying Mr. Liu’s study.

“The stark reality is that high levels of greenhouse gases caused by the combustion of fossil fuels – and the resulting rise in temperature and sea levels and intensification of extreme weather – are having profound consequences for human health and health systems,” Dr. Solomon and colleagues wrote (N Engl J Med. 2019;381:773-4.).

In the new air pollution study, Mr. Liu and colleagues analyzed 59.6 million deaths from 652 cities across 24 countries, “thereby greatly increasing the generalizability of the association and decreasing the likelihood that the reported associations are subject to confounding bias,” wrote John R. Balmes, MD, of the University of California, San Francisco, and the University of California, Berkeley, in an editorial about the study (N Engl J Med. 2019;381:774-6).

The researchers compared air pollution data from 1986-2015 from the Multi-City Multi-Country (MCC) Collaborative Research Network to mortality data reported from individual countries. They assessed PM with an aerodynamic diameter of 10 mcg or less (PM10; n = 598 cities) and PM with an aerodynamic diameter of 2.5 mcg or less (PM2.5; n=499 cities).

Mr. Liu’s team used a time-series analysis – a standard upon which the majority of air pollution research relies. These studies “include daily measures of health events (e.g., daily mortality), regressed against concentrations of PM (e.g., 24-hour average PM2.5) and weather variables (e.g., daily average temperature) for a given geographic area,” Dr. Balmes wrote. “The population serves as its own control, and confounding by population characteristics is negligible because these are stable over short time frames.”

The researchers found a 0.44% increase in daily all-cause mortality for each 10-mcg/m3 increase in the 2-day moving average (current and previous day) of PM10. The same increase was linked to a 0.36% increase in daily cardiovascular mortality and a 0.47% increase in daily respiratory mortality. Similarly, a 10-mcg/m3 increase in the PM2.5 average was linked to 0.68% increase in all-cause mortality, a 0.55% increase in cardiovascular mortality, and 0.74% increase in respiratory mortality.

Locations with higher annual mean temperatures showed stronger associations, and all these associations remained statistically significant after the researchers adjusted for gaseous pollutants.

Although the majority of countries and cities included in the study came from the northern hemisphere, the researchers noted that the magnitude of effect they found, particularly for PM10 concentrations, matched up with that seen in previous studies of multiple cities or countries.

Still, they found “significant evidence of spatial heterogeneity in the associations between PM concentration and daily mortality across countries and regions.” Among the factors that could contribute to those variations are “different PM components, long-term air pollution levels, population susceptibility, and different lengths of study periods,” they speculated.

What makes this study remarkable – despite decades of previous similar studies – is its size and the implications of a curvilinear shape in its concentration-response relation, according to Dr. Balmes.

“The current study of PM data from many regions around the world provides the strongest evidence to date that higher levels of exposure may be associated with a lower per-unit risk,” Dr. Balmes wrote. “Regions that have lower exposures had a higher per-unit risk. This finding has profound policy implications, especially given that no threshold of effect was found. Even high-income countries, such as the United States, with relatively good air quality could still see public health benefits from further reduction of ambient PM concentrations.”

The policy implications, however, extend well beyond clean air regulations because the findings represent just one aspect of climate change’s negative effects on health, which are “frighteningly broad,” Dr. Solomon and colleagues wrote.

“As climate change continues to alter disease patterns and disrupt health systems, its effects on human health will become harder to ignore,” they wrote. “We, as a medical community, have the responsibility and the opportunity to mobilize the urgent, large-scale climate action required to protect health – as well as the ingenuity to develop novel and bold interventions to avert the most catastrophic outcomes.”

The new research and associated commentary marked the introduction of a new NEJM topic on climate change effects on health and health systems.

SOURCE: Liu C et al. N Engl J Med. 2019;381:705-15.

This article was updated 8/22/19.

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