Climate Change and Health Resource Center

Climate Change and Health Resource Center


Healio Interview

Disclosures: Ljungman reports no relevant financial disclosures.
September 17, 2021
6 min read

Q&A: Exposure to pollution levels below current air quality standards linked to mortality


Healio Interview

Disclosures: Ljungman reports no relevant financial disclosures.
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Long-term air pollution exposure at levels below current U.S., European Union and WHO guidelines was significantly associated with mortality from natural causes, CVD and respiratory disease, according to findings published in The BMJ.

The results highlight the need to reconsider existing guidelines and air quality standards, Petter Ljungman, MD, an associate professor of epidemiology at the Institute of Environmental Medicine at Karolinska Institutet and senior consultant of cardiology at Danderyd Hospital in Sweden, and colleagues wrote.

Source quote included in article.

For the Effects of Low-Level Air Pollution: A Study in Europe (ELAPSE) project, which involved six European countries, Ljungman and colleagues analyzed exposure to low levels (below current guidelines) of air pollution concentrations and natural and cause-specific mortality in eight geographic cohorts within Europe. Specifically, they assessed exposure to concentrations of PM2.5, nitrogen dioxide, ozone and black carbon among 325,367 adults over an average of 19.5 years.

They found that higher exposure to PM2.5, nitrogen dioxide and black carbon was significantly associated with death due to natural causes, CVD and respiratory disease. However, ozone exposure did not appear to impact health. An increase of 5 µg/m3 in PM2.5 was linked to a 13% (95% CI, 10.6-15.5) increased risk for natural death. Also, risk for natural death increased by 8.6% (95% CI, 7-10.2) with a 10 µg/m3 increase in nitrogen dioxide. The researchers reported that the associations between mortality and PM2.5, nitrogen dioxide and black carbon remained significant even at low concentrations.

According to findings from a second study published in The Lancet Planetary Health, even short-term exposure to PM2.5 pollutants from wildfires was associated with increased risks for all-cause, respiratory and cardiovascular mortalities. The study, which is the first global study on wildfire pollution, included more than 65.6 million deaths from all causes in 748 cities in 43 countries and regions between Jan. 1, 2000, to Dec. 31, 2016. Researchers found that more than 33,500 deaths occurred annually due to wildfire pollution. According to a press release, the countries with the highest numbers of annual deaths related to wildfire pollution were Japan (more than 7,000 deaths), Thailand (nearly 5,300 deaths), South Africa (more than 5,200 deaths), the U.S. (nearly 3,200 deaths), Mexico (more than 3,000 deaths) and China (more than 1,200 deaths).

Healio Primary Care discussed the findings of both studies with Ljungman to learn more about their implications for public health.

Healio Primary Care: Why did you undertake this research on air pollution exposure guidelines?

Ljungman: Although the evidence demonstrating cardiovascular, cerebrovascular and mortality effects of long-term air pollution exposure has been growing over many years, there has been a paucity of studies specifically targeting the possible effects even below the current air quality guidelines. Previous studies, however, did not seem to indicate a clear lower threshold. In other words, we wanted to know if the current guidelines are sufficient to protect the public from serious health consequences and decided to pool together a large number of high-quality cohorts across Europe to further examine this.

Healio Primary Care: Were you surprised by the results?

Ljungman: No, not surprised as it seems to confirm our hypothesis. It was interesting to see that the associations with stroke were so strong and consistent.

Healio Primary Care: You found that low pollution levels below current guidelines impact public health. What are the health implications of this considering the length of time that we have been operating under inaccurate guidelines?

Ljungman: Yes, we did observe that levels below the current U.S., EU and WHO guidelines were indeed by and large associated with mortality, incident stroke and ischemic heart disease. Since the air quality standards or guidelines have in fact been shown to reduce ambient air pollution levels over time in North America and Europe, the implications are of course that more lives have been lost prematurely and a larger part of the populace have suffered from stroke and myocardial infarction if we had been able to aim and attain higher air quality. The setting of air quality standards is based on a mixture of scientific recommendations based on the evidence and political considerations. The difference in the current guidelines for WHO, the U.S. and EU are a clear example of that because we don’t really expect that the health effects on European citizens and U.S. citizens differ in any significant way.

Healio Primary Care: How should the guidelines be revised to protect public health?

Ljungman: The guidelines should follow the evidence. Air quality policy has been responsible for major improvements in public health and the U.S. Office of Budget Management has previously demonstrated that federal air quality management has been the single most cost-saving federal investment. Lowering the guidelines would very likely lead to additional improvements in public health. Consider also that ambient air pollution is dominated by emissions from combustion processes, the same emissions that contribute to climate change. So, there is a win-win here.

Healio Primary Care: Can you talk about the impact air pollution has on cardiovascular health given your expertise in cardiology?

Ljungman: It has been estimated that ambient air pollution contributes to roughly 25% of all deaths from ischemic heart disease, heart failure and stroke. CVD is definitely the most important impact of air pollution exposure. When I work in the clinic as a cardiologist, I am constantly working with patients who have already developed disease and my focus is on improving their individual outcome, decreasing the risk of further disease or complications and improving their symptoms. But of course, we can easily recognize the huge benefit of making sure that the disease development is avoided all together. In fact, I believe that contributing to healthy air and reducing the ubiquitous exposure to air pollution is an extremely efficient way to reduce the burden of CVDs in our societies, even though I don’t get the benefit of following the progress of my patient.

Healio Primary Care: Considering The BMJ study and the The Lancet Planetary Health study, who are the high-risk populations most impacted by air and wildfire pollution?

Ljungman: This question could be answered in many ways and I am glad you picked it up. Most of us in the field would point to a number of different vulnerable groups: definitely the elderly, those with existing cardiovascular or respiratory diseases, diabetics and pregnant women. Effects have also been observed for lung function and allergies in children, and it also seems that air pollution increases the risk of dementia and cognitive function. So, in establishing any air quality guideline, we need to make sure that these groups are still protected as they are most likely to be affected. But the wildfires also highlight another aspect. Wildfires lead to very, very high levels of ambient air pollution, and this is alarming, especially since they seem to be recurring and affect large human dwellings. They also emit heat and occur during heat waves, and studies that we and others have been involved in have indicated that there may be interactive effects between air pollution and heat. Put more clearly, the health hazards of heat and the health hazards from air pollution actually magnify each other’s effects such that 1+1=3. Furthermore, the level we might observe in wildfires are actually similar to what you might see in some lower-middle income countries like megacities in India. In fact, while we are mostly discussing room for improvement in Europe and North America, the vast challenge is in Asia, Africa and South America, where most of the burden of disease from air pollution lies. This is also why we are together with U.S. researchers collaborating with scientists in India to specifically address these challenges.

Healio Primary Care What can primary care physicians do to protect their patients now as the guidelines are inaccurate and that wildfires are becoming more frequent?

Ljungman: Primary care physicians should continue to address primary prevention and minimize important risk factors such as smoking, obesity, physical inactivity, diet and other well-known risk factors that on the individual level have a higher impact on their patients as well as are more amenable to individual level intervention. But I think understanding how air pollution might figure in the whole equation is important, both in communicating with patients and in any community outreach or speaking with policymakers. Primary care physicians should be aware and expect greater numbers of asthma and COPD exacerbations with the wildfires and a greater risk of myocardial infarctions and cardiac arrests during these episodes, make sure their patients are compliant with their recommended medications and perhaps consider HEPA filters, air purifiers for high-risk patients like in senior care facilities. Asthmatics may need to temporarily increase their regular treatment.

Healio Primary Care Anything else to add regarding the association between health and air pollution?

Ljungman: The flipside of the negative effects of air pollution is that they are actually amenable to reductions through policy intervention, and we have ample evidence of this in the U.S. and EU. We can actually do something about it. Also, whatever we do to reduce air pollution will also mitigate climate change in the long term, so it merits significant investment in effort and funding. Also, look out for the new updated WHO air quality guidelines that will be released on Sept 22, 2021.


Chen G, et al. Lancet Planet. 2021;doi:10.1016/S2542-5196(21)00200-X.

EurekAlert! First global study of wildfire pollution reveals increase in mortality rate. Accessed September 13, 2021.

Strak M, et al. The BMJ. 2021;doi:10.1136/bmj.n1904.