If you can read this, you’re undoubtedly breathing. This seemingly simple act is a surprisingly complex affair.
It means inhaling oxygen through your nose or mouth until it reaches your lungs, which deliver that oxygen to the bloodstream. The blood then passes it along to every cell in your body. In the cells, the oxygen trades places with carbon dioxide, and the blood carries that back to the lungs so it can ride out on the exhale. All day, every day, all the time.
How cool is that?
Just as the heart keeps us alive by pumping blood, the lungs sustain us with respiration. And we rarely give it much attention — which is just how the body wants it. The autonomic nervous system controls breathing so we don’t have to think about it.
Yet there are times when we do need to think about breathing, and now is one of them. Lung health is heavily dependent on the quality of the air we share, and pollution is making that air steadily worse. Meanwhile, research is revealing more about the diverse roles the lungs play in our overall health, including immunity and even autoimmune disorders.
It may be tempting to ignore these issues that effect lung health because we feel powerless to change them, but that prevents us from learning all we can about how to protect our lungs and their microbiome (yes, the lungs have a microbiome!), as well as our air quality.
And there is a lot we can do.
A pair of lungs contains five lobes — three in the right lung, two in the left. (The left lung is smaller to make space for the heart.) Each lobe resembles a balloon full of spongy tissue wrapped in a protective membrane called the pleura, which separates the lungs from the chest wall.
Air reaches the lungs through the trachea, or windpipe, which splits into five bronchial tubes, one for each lobe. These branch into many smaller tubes called bronchioles, each one tipped by a tiny air sac called an alveolus; together, it all looks like an upside-down tree. The lungs contain more than 400 million alveoli, which would cover a soccer field if unfolded. Capillaries lining the walls of these air sacs help exchange oxygen and carbon dioxide.
The respiratory system is well- equipped to handle airborne toxins, and our pulmonary enforcers take many forms. The nose, for instance, is lined with little hairs to trap pollutants; it also warms and humidifies the air before it reaches the lungs — both good reasons to breathe through the nose whenever possible.
Bronchial tubes are lined with sticky mucus and tiny hairlike structures called cilia. The mucus traps dust, germs, and other unwanted schmutz, while the cilia sweep it continuously upward on what pulmonologist Brian Christman, MD, calls the “mucociliary escalator.” Then we sneeze or cough it out. (That’s why cough suppressants are not always a good idea.)
The lungs also have innate immune function. “The lung has its own rich set of cells that engage the immune system,” says Christman, who is vice-chair of clinical affairs at Vanderbilt University’s Department of Medicine.
Alveoli, for example, contain cellular macrophages, which clear out pathogenic bacteria.
But that’s not all. Researchers have recently discovered that the lungs’ innate immune system is more complex than they once thought. While the lungs were once believed to be largely sterile, they now appear to have their own resident microbes, or microbiome.
When it’s healthy, this microbial population is small and stable compared with the thriving, constantly changing community in the gut. (If the gut microbiome is the Amazon rainforest, the lung microbiome is Antarctica.) Yet the lung microbiome may also play a role in the body’s overall immune response.
A 2018 University of Michigan study found that a common antibiotic significantly altered the lung microbiome in mice. Researchers also observed that the lung’s microbiota responded to infection independently of the gut’s. Study leader Robert Dickson, MD, says this required his team to rethink its assumptions about the lung’s role in immunity.
“We tend to think of the relationship between lung bacteria and lung immunity as ‘off’ or ‘on’: Either your immune system is asleep in health or it’s revved up during infections,” Dickson notes. “Our study suggests that it’s much more of a continuum. . . . The lung’s immune cells are constantly doing surveillance, dialing their response up or down according to what bugs they’re seeing.”
This wonkish medical discovery is important for all of us: It suggests that our lungs influence more than just our respiratory health.
Functional-medicine physician Robert Rountree, MD, sees the relationship between the lungs and the immune response as especially relevant in today’s environment. He suspects imbalanced lung microbiomes may even contribute to the dramatic rise in autoimmune diseases, which now affect as many as 50 million Americans.
“We talk a lot about what our patients are eating,” says Rountree. “But what are they breathing?”
Autoimmunity occurs when a hyperactive immune system attacks the body’s own tissues. With multiple sclerosis, for example, the immune system destroys the nerves’ myelin lining; in alopecia, the hair follicles. Rountree notes that a top risk factor for autoimmune rheumatoid arthritis, in which the immune system targets joint tissue, is cigarette smoking. This elevated risk lasts for a decade or longer after the person has quit.
Research on the lung microbiome is still in its early stages, he acknowledges, but the parallels between the lung and the gut are important.
“We know that if somebody smokes, or if they have chronic lung disease, they’re going to have an unhealthy microbiome,” Rountree says. “The bacteria in the lungs communicate with the cells that line the lungs, and that helps control the thickness of the mucus, which is a big part of the protective barrier.” Mucus plays a key protective role in other parts of the body as well, including the gut.
And that’s not the only parallel.
“There are tight junctions in the lungs that are very similar to the gut,” he adds, and these may loosen when they’re chronically irritated by smoke or other particulate matter. This can lead to a condition he calls “leaky lung.”
“Leaky lungs allow bacteria and other substances to get into the space beneath the surface of the lung, so the immune cells located there are revved up.” This triggers a chronic inflammatory response — the first stage of autoimmunity.
Chronic irritation and inflammation may activate an enzyme called peptidylarginine deiminase.
This enzyme converts the amino acid arginine, which is found in proteins lining the lungs, into citrulline. The process alters the structure of the proteins, and the body no longer recognizes them.
The immune cells see this newly formed citrulline — something harmless in its usual context — as a hostile invader, and they develop antibodies called anti-citrullinated peptides to vanquish it.
In lab tests, these peptides are the first indicator that a person is on the path to rheumatoid arthritis, Rountree says. “Somehow, air pollutants activate this whole system in the body.”
Physicians often address leaky gut by recommending that their patients consume fewer inflammatory foods and take some key supplements. This raises a question: Does healing leaky lungs require changing what we breathe? Rountree’s answer is a qualified yes.
“The first thing is to avoid exposure,” he says. This means that if you smoke, it’s vital to get the support you need to quit.
But avoiding other airborne pollutants is tricky in today’s environment.
The United States has seen an uptick in air-quality warnings in recent years. According to a 2019 report by the American Lung Association, about four in 10 Americans live in counties with unhealthy levels of ozone or particle pollution.
The last three years were the hottest on record, and rising temperatures linked to climate change have increased the risk of wildfires as well as pollen production, both of which contribute significantly to particle pollution in the air. (Studies at Johns Hopkins have found that ragweed and other pollen plants thrive in a carbon-rich atmosphere.)
Worldwide, nine in 10 people now breathe air that exceeds pollution limits set by the World Health Organization.
Traffic emissions in the United States have declined thanks to stronger regulations on cars and trucks, but recent research suggests that volatile organic compounds (VOCs) from household and industrial products now contribute as many atmospheric particulates as vehicles do. According to the ongoing HOMEChem study and other analyses, the average home may now contain as many airborne particulates as the air outside does, largely because of emissions from items like plastic shower curtains, vinyl flooring, cleaning products, and cooking — to name a few.
Exposure to airborne pollution, both indoor and outdoor, results most visibly in respiratory disorders. About 24.6 million Americans — more than 6 million of them children — have been diagnosed with asthma, according to the Environmental Protection Agency (EPA).
And Christman says the risk of asthma and other respiratory illnesses (as well as related autism and other cognitive conditions) is greater for people living near power plants and busy roadways.
“The health risks of air pollution are real,” he notes. “Those who live closest to the emitter source are most at risk.” Lower-income communities are more likely to be downwind of polluting sources and suffer the effects of air pollution disproportionately, he adds.
Still, no one is immune.
Outdoor-air quality in the United States has improved substantially since the 1963 Clean Air Act, which gained regulatory traction in 1970 with the formation of the EPA. In addition to nearly eliminating airborne lead by banning lead-based gasoline, the act has helped reduce ground-level ozone levels (a key component of smog) by 25 percent since 1980, cut mercury emissions almost in half since 1990, and reduced sulfur-dioxide emissions by 71 percent since 1980.
Yet the Clean Air Act is in trouble. In August 2018 the Trump administration rolled back restrictions on emissions from coal-burning power plants. It also announced plans to loosen emissions standards for cars and light trucks, and proposed dismantling regulations on mercury emissions from power plants. If implemented, these actions will dramatically worsen air quality and accelerate climate change.
The current, politicized EPA has also sought to discredit previous research on the health risks of PM 2.5, the category of the very smallest types of airborne particulate. A newly appointed advisory committee has been tasked with “reassessing” decades of studies showing its dangers. That reassessment could dismantle significant aspects of the Clean Air Act.
Christman and other experts are most concerned about PM 2.5 particles. These molecules are about one-thirtieth the thickness of a human hair — too small for the lungs’ defense system to process.
“These tiny particles float in with our breath and penetrate to the smallest air sacs,” Christman explains. “They cross over the lung–blood barrier and enter the circulatory system, increasing the risk of heart attack and stroke.”