Air Pollution and Covid-19: A Potential Link?
As the Covid-19 pandemic continues, scientists are tirelessly investigating what factors might make people more vulnerable to infection. One intriguing possibility is air pollution, specifically inhalable particles smaller than 2.5 micrometers in diameter (PM2.5). This type of pollution has been linked to a wide array of respiratory problems, among other health outcomes. Covid-19 is a respiratory illness, so there’s reason to think that PM2.5 exposure might affect people’s response to Covid-19, too.
So how might pollution relate to Covid-19? There are two main pathways. First, pollution itself might make people more vulnerable to getting the virus or to having worse outcomes if they are infected. And second, pollution can contribute to the development of chronic conditions, which in turn put people at greater risk.
Vulnerability to Respiratory Issues
First, let’s discuss how exposure to air pollution generally appears to increase people’s susceptibility to respiratory infections. Although scientists aren’t sure exactly how, one possibility appears to be by causing inflammation in the body, which in turn weakens our defenses against infections. Another possibility that’s being explored is whether pollutant particles increase the infectivity of viruses in the air.
A well-studied example is lower respiratory infections – which are often caused by viruses. The Global Burden of Disease study estimates that over 44 million years of healthy life are lost annually due to lower respiratory infections caused by particulate matter pollution. Researchers in a large-scale study in Utah found that each short-term increase of 10 micrograms per cubic meter (μg/m3) in PM2.5 levels was linked to respiratory issues. Specifically, the odds of a healthcare encounter for an acute lower respiratory infection rose 15-32% across age groups.
The effect of air pollution on respiratory disease was also shown during the SARS epidemic — a disease caused by another coronavirus and closely related to Covid-19. One study found that SARS patients living in areas with the highest levels of air pollution were much harder-hit when they got sick: They were twice as likely to die from SARS compared to patients who were living in areas with the cleanest air.
So what does this mean for Covid-19? Although we’re still early in the pandemic and it will take some time for researchers to gather and analyze data, a similar pattern seems to be emerging. Early evidence from the Harvard T.H. Chan School of Public Health indicates that people who live in areas with higher air pollution have a greater risk of severe outcomes from Covid-19. Specifically, an increase of just 1 μg/m3 in long-term PM2.5 exposure appears to be associated with a 8% increase in the Covid-19 mortality rate. (For reference, the EPA’s standard for public health protection is that PM2.5 levels in any area should not exceed 12 μg/m3.) The researchers noted that the magnitude of this association between PM2.5 and Covid-19 mortality is 11 times higher than that of PM2.5 and mortality generally. Another study examined another pollutant, nitrogen dioxide (NO2), across 66 administrative regions in several hard-hit European countries. The author found overlapping “hotspots” of NO2 levels and fatalities from Covid-19 cases, and concluded that “long-term exposure to this pollutant may be one of the most important contributors to fatality caused by the COVID-19 virus.”
Chronic Conditions That Carry A Higher Covid-19 Risk
Based on the evidence and information currently available, not everyone is at the same level of risk if they become infected with Covid-19. People who have chronic health conditions such as ischemic heart disease (IHD), diabetes, chronic kidney disease, and severe obesity are at a greater risk for becoming severely ill if they get infected. In addition, people with respiratory conditions such as chronic obstructive pulmonary disease (COPD) or asthma also belong to a greater risk category and have been hospitalized more frequently than those without chronic lung issues.
Most of these conditions are lifestyle-related, and behaviors such as insufficient physical activity, poor nutrition, and excessive alcohol intake play a significant role. However, other factors contribute too, such as air pollution. PM2.5 pollution specifically is associated with the development of some of these conditions, and its contribution is substantial. For example, the attributable risk of PM2.5 in the development of IHD is more than half of that of smoking: globally, over 40.5 million healthy years of life are lost due to IHD because of smoking, while nearly 22 million are lost due to IHD because of particulate matter pollution.
Ambient particulate matter pollution is also second only to smoking when it comes to COPD development, resulting in more than 15.5 million healthy years of life lost globally every year. Ambient PM2.5 pollution is also known to exacerbate the symptoms of some of these conditions. For example, PM2.5 is known to trigger symptoms of asthma in people who already have it. Indeed, levels as low as 4-7 μg/m3 have been associated with an increased prevalence of asthma symptoms (for reference, these levels are below the 12 μg/m3 threshold recommended by the EPA).
Finally, there is some evidence that ambient pollution plays a role in the development of asthma, not just in triggering asthma symptoms in individuals who are already asthmatic. For example, prenatal exposure to PM2.5 has been associated with an increased risk of childhood asthma development in boys by age 6.
In the US, six out of 10 adults have a chronic disease, and four out of 10 have two or more. The chronic diseases that are associated with ambient particulate matter, which also increase the risk of serious illness or death from Covid-19, are also quite common. Over 30.6 million people in the US have type 2 diabetes, 20.8 million have COPD, 9.5 million have IHD, and 16.2 million have asthma. Globally, the number of cases for these conditions, plus asthma, exceeds a billion. A substantial proportion of the population both in the US and across the world is therefore at greater vulnerability for severe cases and complications due to the novel coronavirus because of their chronic conditions; this is in addition to those who are at a greater vulnerability because of their older age or immunocompromised conditions.
While air pollution levels have been seeing a dramatic decrease everywhere due to a drop in manufacturing, travel, and other emission-producing activities, this doesn’t mean that people who are now breathing cleaner air are therefore at a lower risk of Covid-19 complications. Unfortunately, the effects of air pollution harm the respiratory system and lead to related chronic conditions over many years or decades, so a drop of several weeks or months in pollution levels does not translate to lower risk.
What Can We Do?
The most effective long-term approaches to reducing ambient air pollution include switching to cleaner types of energy and reducing or reversing decades of intense air pollution worldwide; unfortunately we don’t have the luxury of time when it comes to responding to the novel coronavirus pandemic. At this moment, while people around the world are spending most of their time at home in order to help curb the spread of the virus, it makes sense to focus on our indoor air quality (IAQ). Managing our IAQ could potentially result in better Covid-19 outcomes while promoting our overall health and well-being. And over time, better air quality matters in the context of chronic conditions as well as for our overall health.
There are several steps that you can take to ensure better air quality at home, including:
- Ventilation First. Whether you have a mechanical ventilation system or rely on natural ventilation (i.e., windows), make sure that your space does not lack fresh air. A general guideline is for carbon dioxide (CO2), a key indicator of air freshness, not to exceed 600-800 ppm. You can tell if there’s a lack of fresh air when a room smells “stuffy”; this is due to a higher concentration of CO2. In fact, CO2 concentrations can easily reach several times those recommended for indoor environments. For example, sleeping in a poorly ventilated bedroom can lead to CO2 levels above 2,000 ppm over the course of the night.
- Air Purification. Indoor sources of air pollution include cooking, off-gassing from materials and indoor finishes, and polluted outdoor air that makes its way indoors. Air purifiers can help to ensure that the air you breathe is clean and free of harmful pollutants. Many standalone air purifiers are readily available (although shipping times may be delayed due to the coronavirus), but it can be tricky to pick a good one. Stay tuned for a follow-up blog post focused on how to pick the best air purifier for your home. If you already use an air purifier, make sure to place it in a room or area that you frequently occupy, or consider getting multiple air purifiers to cover the bulk of your home.
- Air Quality Monitoring. IAQ sensors can measure the levels of a range of pollutants, including CO2, PM2.5, PM10, total volatile organic compounds (TVOCs), and ozone. Knowing the levels of these pollutants inside your home can help you take action to improve your air quality. Meanwhile, looking up outdoor air quality in your area can help you decide when to open your windows to let in fresh air, as doing so when outdoor air quality is poor could lead to a decrease in IAQ.
Edited by Radhika Singh
This post was updated on June 29, 2020 to reflect updated research findings.