How The Environment Shapes The Health Within Us

The author, Sen. Bill Frist, MD, performing a heart surgery at Vanderbilt University Medical Center.

Vanderbilt University Medical Center

I spent much of my early career looking directly at hearts and lungs through an opened chest in the operation room. As a heart and lung transplant surgeon, I saw these organs at their most vulnerable. A failing heart, scarred lungs, impaired circulation, and inadequate oxygen. In the operating room, disease is never abstract. It is an intensely physical reality.

Over time, and later through my work for 12 years in the U.S. Senate, I came to think more broadly about what makes people sick in the first place. We rightly focus on blood pressure, cholesterol, smoking, genetics, infection, diet, and exercise. But another set of equally powerful forces is acting on us every day: the air we breathe, the heat we endure, the smoke we inhale, the landscapes surrounding us, and the chronic stress created by environmental disruption.

The science now allows us to see those forces, too, at work inside the body. Climate change and environmental degradation increasingly show up in the heart, lungs, kidneys, nervous system, hormonal stress response, and immune system. It’s medical science, and it affects each and every one of us. Environmental quality is a personal health issue. And it should shape how physicians, communities, and policymakers respond.

The heart, where I focused most of my medical career at Stanford and Vanderbilt, offers one of the clearest examples. Fine particulate pollution, known as PM_2.5, is small enough to penetrate deep into the lungs and trigger inflammation, vascular dysfunction, and autonomic stress. The American Heart Association has long recognized particulate pollution as a major cardiovascular risk factor. More recent research links extreme heat, worsening air quality, and severe weather with higher rates of heart attack, stroke, heart failure, and cardiovascular death.

Heat creates its own cardiovascular load. As the body tries to cool itself, blood vessels dilate, the heart works harder and harder, and fluid losses increase. For an older adult, an outdoor worker, or someone living with heart disease, a stretch of extreme heat can quickly become an urgent medical event.

The author and surgical team conducting a heart transplant in the first years of the Vanderbilt Transplant Center. Today, the Center is the busiest heart transplant center in the world.

Vanderbilt University Medical Center

After the heart, the organ I most frequently operated on was the lung. Lungs are our most intimate interface with the environment. Every breath (and we take over 20,000 breaths every day) brings the outside world directly into the body. Wildfire smoke, ozone, particulate pollution, and longer pollen seasons all inflame airways, worsen asthma and COPD (chronic obstructive pulmonary disease like bronchitis and emphysema), increase respiratory infections, and drive hospitalizations. Children in particular, deserve special attention here because their lungs are still developing.

One of the most encouraging studies in this field followed children in Southern California as air quality improved over nearly two decades. Those living in communities with the largest reductions in pollution experienced the greatest gains in lung function. Think about what that means. Cleaner air changed the physical development of children’s lungs, leading to healthier lives. That is preventive medicine practiced at community scale.

And the evidence extends well beyond the chest.

The kidneys depend on stable blood flow, hydration, and internal chemistry. Repeated heat exposure and dehydration can produce acute kidney injury and, over time, may contribute to chronic kidney disease. This is a risk that grows for outdoor workers and agricultural laborers as temperatures rise. Air pollution, also, takes its own toll. A major study involving roughly 2.5 million U.S. veterans found, for example, that long term PM_2.5 exposure was associated with greater risk of chronic kidney disease, faster loss of kidney function, and progression to end stage renal disease.

Beyond individual organs, environmental factors also affect the systems that coordinate how those systems work together.

The autonomic nervous system constantly balances sympathetic activity, our “fight or flight” response, with parasympathetic activity, the “rest and recover” system that slows the heart, regulates blood pressure, and helps restore equilibrium. Pollution pushes that balance toward physiological stress. Studies have linked particulate exposure with reduced heart rate variability, a marker of impaired autonomic regulation.

Haze from Canadian wildfires obscures the Statue of Liberty as seen from Brooklyn Bridge Park on July 17, 2026 in New York City. New York City was under an Air Quality Health Advisory as the Canadian and Great Lakes wildfire smoke moved through the area, creating a thick haze in the heat. (Photo by Spencer Platt/Getty Images)

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Nature, though, can also move us in the other, more positive direction. A large Japanese field study found that people walking in forest environments were more likely to show increased parasympathetic activity and reduced sympathetic activity than people walking in urban settings. Other research suggests that even viewing green environments can improve physiological recovery after stress. I find that especially compelling. Anyone who has walked through a forest, sat beside a river or spent time in nature understands the feeling of the body settling to a calmer and more relaxed place. Science is now measuring what most of us have experienced intuitively.

The same pattern appears in the hormonal stress system. The hypothalamic-pituitary-adrenal axis releases cortisol (the “stress hormone”) and other hormones when we perceive a threat. That response can save a life. But repeated or sustained activation wears on the body and can measurably contribute to heart and blood vessel disease, metabolic dysfunction, anxiety, and depression. One elegant, randomized crossover experiment compared periods of purified indoor air with typical, unfiltered exposure and found that higher particulate pollution was associated with increases in cortisol, cortisone, epinephrine and norepinephrine. Dirty air, in other words, can register as biological stress and disease.

Temperature matters here too. A 2023 systematic review and meta-analysis of 114 studies found that higher temperatures were associated with worse mental health outcomes, more psychiatric hospital visits and higher suicide rates. A warming environment reaches far beyond heat exhaustion and physical health. It can affect the systems that govern mood, behavior, and resilience.

The immune system adds another layer. Air pollution, extreme heat, wildfire smoke, and changing allergen patterns can promote chronic inflammation and disrupt immune regulation. One population study of more than 80,000 people linked long term particulate exposure with higher rates of autoimmune disease. And other recent research describes effects on barrier defenses in the lungs, skin and gastrointestinal tract.

Here the story begins to turn from damage toward restoration. My perspective is colored by my direct experiences in my capacity as board chair of The Nature Conservancy globally.

Healthy, natural, biodiverse environments help support more balanced immune function through exposure to a richer microbial world. Green space has also been associated with lower mortality, even after researchers account for factors such as air pollution and noise. The pathways are likely several: more physical activity, lower stress, stronger social connection and physiological recovery.

This is why I believe we should move beyond thinking of nature simply as something beautiful to protect. Our natural systems should be viewed as part of the infrastructure of human health. It’s not just conservation for conservation’s sake; it’s conservation for humanity’s sake.

Young family walking on a forest path in autumn.

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For physicians, that means widening the environmental history when we first see a patient. Where does this person work? How much heat are they exposed to? Are they breathing wildfire smoke, or living near heavy traffic? Do they have shade, trees, parks and safe places to exercise?

For health systems, resilience increasingly belongs in preparedness. Heat waves, smoke events, storms, and prolonged power outages create predictable patterns of illness. Hospitals and community health organizations can actively plan around them.

For policymakers, the opportunity is larger still. Clean air standards are preventive medicine, and efforts in Washington to undo them are misguided. Urban trees and shade reduce heat exposure, and parks and greenways support exercise, stress reduction, and social connection. Investments in healthier environments can lower disease burden long before a patient reaches an emergency room or wind up on the operating table.

I have spent years in medicine and public policy, two fields that often meet only after a problem becomes urgent. Our growing understanding of environmental health gives us a rare opportunity to act earlier instead.

Medicine has always understood prevention. We vaccinate before infection. We treat high blood pressure before stroke. We lower cholesterol before a heart attack. We encourage exercise before frailty. The same logic belongs in environmental policy.

My wife Tracy Frist and I being expertly guided down the river by Solitude River Trips guide Ashley, capturing a moment in a calm stretch of the Salmon. This August we spent a week off the grid on the river in Idaho to recharge and reconnect with nature.

Tracy Frist

Cleaner air, safer temperatures, healthier landscapes and greater access to nature improve the conditions in which human biology operates. They complement medical care while reducing the heavy burden that eventually arrives at the clinic, the hospital, and the operating room.

I began my career looking inside the chest, caring for hearts and lungs at their most vulnerable. Decades later, I see health through a wider lens, and I know the real objective is to intervene long before a person ends up on the operating table. The environment shapes our health, literally with every single breath we take.